MVStore: simpler API

h2/src/main/org/h2/mvstore/MVMap.java

@@ -847,7 +847,7 @@ public class MVMap<K, V> extends AbstractMap<K, V>
      * Forget those old versions that are no longer needed.
      */
     void removeUnusedOldVersions() {
-        long oldest = store.getRetainOrStoreVersion();
+        long oldest = store.getOldestVersionToKeep();
         if (oldest == -1) {
             return;
         }

h2/src/main/org/h2/mvstore/MVStore.java

@@ -57,6 +57,10 @@ MVTableEngine:
 TransactionStore:
 
 MVStore:
+- better document auto-commit (also when many unsaved pages)
+    advantages and disadvantages
+- auto-commit when used in memory as well
+- better document MVStore setters
 - automated 'kill process' and 'power failure' test
 - update checkstyle
 - feature to auto-compact from time to time and on close
@@ -124,7 +128,7 @@ MVStore:
 - fix documentation (including examples)
 - autocommit commits, stores, and compacts from time to time;
     the background thread should wait at least 90% of the
-    configured write delay to store changes 
+    configured write delay to store changes
 - currently, uncommitted changes are stored if there are many transient changes,
     and rolled back when opening - is this really needed?
 - compact* should also store uncommitted changes (if there are any)
@@ -177,8 +181,7 @@ public class MVStore {
     /**
      * The map of chunks.
      */
-    private final ConcurrentHashMap<Integer, Chunk> chunks =
-            new ConcurrentHashMap<Integer, Chunk>();
+    private final ConcurrentHashMap<Integer, Chunk> chunks = new ConcurrentHashMap<Integer, Chunk>();
 
     /**
      * The map of temporarily freed storage space caused by freed pages. The key
@@ -189,12 +192,12 @@ public class MVStore {
             new ConcurrentHashMap<Long, HashMap<Integer, Chunk>>();
 
     /**
-     * The metadata map. Write access to this map needs to be synchronized on the store.
+     * The metadata map. Write access to this map needs to be synchronized on
+     * the store.
      */
-    private MVMap<String, String> meta;
+    private MVMapConcurrent<String, String> meta;
 
-    private final ConcurrentHashMap<Integer, MVMap<?, ?>> maps =
-            new ConcurrentHashMap<Integer, MVMap<?, ?>>();
+    private final ConcurrentHashMap<Integer, MVMap<?, ?>> maps = new ConcurrentHashMap<Integer, MVMap<?, ?>>();
 
     private HashMap<String, String> storeHeader = New.hashMap();
 
@@ -202,7 +205,7 @@ public class MVStore {
 
     private int lastMapId;
 
-    private long retainVersion = -1;
+    private int versionsToKeep = 5;
 
     /**
      * Whether to compress new pages. Even if disabled, the store may contain
@@ -222,14 +225,13 @@ public class MVStore {
     private long lastStoredVersion;
 
     /**
-     * The estimated number of unsaved pages
-     * (this number may not be completely accurate,
-     * because it may be changed concurrently, and
-     * because temporary pages are counted)
+     * The estimated number of unsaved pages (this number may not be completely
+     * accurate, because it may be changed concurrently, and because temporary
+     * pages are counted)
      */
     private int unsavedPageCount;
-    private int unsavedPageCountMax;
-    private boolean storeNeeded;
+    private int autoCommitPageCount;
+    private boolean saveNeeded;
 
     /**
      * The time the store was created, in milliseconds since 1970.
@@ -237,7 +239,7 @@ public class MVStore {
     private long creationTime;
     private int retentionTime;
 
-    private long lastStoreTime;
+    private long lastCommitTime;
 
     /**
      * The earliest chunk to retain, if any.
@@ -248,15 +250,15 @@ public class MVStore {
      * The version of the current store operation (if any).
      */
     private volatile long currentStoreVersion = -1;
-    
+
     private Thread currentStoreThread;
 
     private volatile boolean metaChanged;
 
     /**
-     * The delay in milliseconds to automatically store changes.
+     * The delay in milliseconds to automatically commit and write changes.
      */
-    private int writeDelay;
+    private int autoCommitDelay;
 
     /**
      * Create and open the store.
@@ -272,7 +274,8 @@ public class MVStore {
         pageSplitSize = o == null ? 6 * 1024 : (Integer) o;
         o = config.get("backgroundExceptionHandler");
         this.backgroundExceptionHandler = (UncaughtExceptionHandler) o;
-        meta = new MVMap<String, String>(StringDataType.INSTANCE, StringDataType.INSTANCE);
+        meta = new MVMapConcurrent<String, String>(StringDataType.INSTANCE,
+                StringDataType.INSTANCE);
         HashMap<String, String> c = New.hashMap();
         c.put("id", "0");
         c.put("createVersion", Long.toString(currentVersion));
@@ -295,21 +298,21 @@ public class MVStore {
             int averageMemory = Math.max(10, pageSplitSize / 2);
             int segmentCount = 16;
             int stackMoveDistance = maxMemoryBytes / averageMemory * 2 / 100;
-            cache = new CacheLongKeyLIRS<Page>(
-                    maxMemoryBytes, averageMemory, segmentCount, stackMoveDistance);
+            cache = new CacheLongKeyLIRS<Page>(maxMemoryBytes, averageMemory,
+                    segmentCount, stackMoveDistance);
         }
-        o = config.get("writeBufferSize");
+        o = config.get("autoCommitBufferSize");
         mb = o == null ? 4 : (Integer) o;
-        int writeBufferSize =  mb * 1024 * 1024;
+        int autoCommitBufferSize = mb * 1024 * 1024;
         int div = pageSplitSize;
-        unsavedPageCountMax = writeBufferSize / (div == 0 ? 1 : div);
+        autoCommitPageCount = autoCommitBufferSize / (div == 0 ? 1 : div);
         char[] encryptionKey = (char[]) config.get("encryptionKey");
         try {
             fileStore.open(fileName, readOnly, encryptionKey);
             if (fileStore.size() == 0) {
                 creationTime = 0;
                 creationTime = getTime();
-                lastStoreTime = creationTime;
+                lastCommitTime = creationTime;
                 storeHeader.put("H", "3");
                 storeHeader.put("blockSize", "" + BLOCK_SIZE);
                 storeHeader.put("format", "" + FORMAT_WRITE);
@@ -348,14 +351,13 @@ public class MVStore {
                 Arrays.fill(encryptionKey, (char) 0);
             }
         }
-        lastStoreTime = getTime();
-
-        // setWriteDelay starts the thread, but only if
-        // the parameter is different than the current value
+        lastCommitTime = getTime();
 
-        o = config.get("writeDelay");
-        int writeDelay = o == null ? 1000 : (Integer) o;
-        setWriteDelay(writeDelay);
+        // setAutoCommitDelay starts the thread, but only if
+        // the parameter is different from the old value
+        o = config.get("autoCommitDelay");
+        int delay = o == null ? 1000 : (Integer) o;
+        setAutoCommitDelay(delay);
     }
 
     /**
@@ -380,7 +382,8 @@ public class MVStore {
      * @return the read-only map
      */
     @SuppressWarnings("unchecked")
-    <T extends MVMap<?, ?>> T  openMapVersion(long version, int mapId, MVMap<?, ?> template) {
+    <T extends MVMap<?, ?>> T openMapVersion(long version, int mapId,
+            MVMap<?, ?> template) {
         MVMap<String, String> oldMeta = getMetaMap(version);
         String r = oldMeta.get("root." + mapId);
         long rootPos = DataUtils.parseLong(r, 0);
@@ -468,7 +471,7 @@ public class MVStore {
      * root.{mapId} = {root position}
      * setting.storeVersion = {version}
      * </pre>
-     * 
+     *
      * @return the metadata map
      */
     public MVMap<String, String> getMetaMap() {
@@ -512,7 +515,7 @@ public class MVStore {
         metaChanged = true;
     }
 
-    private void readMeta() {
+    private synchronized void readMeta() {
         chunks.clear();
         Chunk header = readChunkHeader(rootChunkStart);
         if (header.start == Long.MAX_VALUE) {
@@ -569,7 +572,8 @@ public class MVStore {
         // we don't know which chunk is the newest
         long newestChunk = -1;
         // read the last block of the file, and then the two first blocks
-        ByteBuffer buffLastBlock = fileStore.readFully(fileStore.size() - BLOCK_SIZE, BLOCK_SIZE);
+        ByteBuffer buffLastBlock = fileStore.readFully(fileStore.size()
+                - BLOCK_SIZE, BLOCK_SIZE);
         ByteBuffer buffFirst2Blocks = fileStore.readFully(0, BLOCK_SIZE * 2);
         ByteBuffer buff = ByteBuffer.allocate(3 * BLOCK_SIZE);
         buff.put(buffLastBlock);
@@ -611,7 +615,8 @@ public class MVStore {
         }
         if (currentVersion < 0) {
             throw DataUtils.newIllegalStateException(
-                    DataUtils.ERROR_FILE_CORRUPT, "Store header is corrupt: {0}", fileStore);
+                    DataUtils.ERROR_FILE_CORRUPT,
+                    "Store header is corrupt: {0}", fileStore);
         }
         setWriteVersion(currentVersion);
         lastStoredVersion = -1;
@@ -647,10 +652,7 @@ public class MVStore {
     }
 
     /**
-     * Close the file and the store. If there are any uncommitted changes, they
-     * are written to disk first. All open maps are closed.
-     * <p>
-     * It is not allowed to concurrently call close and store.
+     * Close the file and the store. Unsaved changes are written to disk first.
      */
     public void close() {
         if (closed) {
@@ -659,7 +661,7 @@ public class MVStore {
         if (fileStore != null && !fileStore.isReadOnly()) {
             stopBackgroundThread();
             if (hasUnsavedChanges()) {
-                store();
+                commitAndSave();
             }
         }
         closeStore(true);
@@ -722,6 +724,11 @@ public class MVStore {
         int chunkId = DataUtils.getPageChunkId(pos);
         Chunk c = chunks.get(chunkId);
         if (c == null) {
+            if (!Thread.holdsLock(this)) {
+                throw DataUtils.newIllegalStateException(
+                        DataUtils.ERROR_INTERNAL,
+                        "Unsynchronized metadata read");
+            }
             String s = meta.get("chunk." + chunkId);
             if (s == null) {
                 throw DataUtils.newIllegalStateException(
@@ -747,18 +754,22 @@ public class MVStore {
     }
 
     /**
-     * Commit the changes. This method marks the changes as committed and
-     * increments the version.
+     * Commit the changes.
      * <p>
-     * Unless the write delay is set to 0, this method does not write to the
-     * file. Instead, data is written after the delay, manually by calling the
-     * store method, when the write buffer is full, or when closing the store.
+     * For in-memory stores, this method increments the version.
+     * <p>
+     * For persistent stores, it also writes changes to disk. It does nothing if
+     * there are no unsaved changes, and returns the old version. It is not
+     * necessary to call this method when auto-commit is enabled (the default
+     * setting), as in this case it is automatically called from time to time or
+     * when enough changes have accumulated. However, it may still be called to
+     * flush all changes to disk.
      *
      * @return the new version
      */
     public long commit() {
         if (fileStore != null) {
-            return store();
+            return commitAndSave();
         }
         long v = ++currentVersion;
         setWriteVersion(v);
@@ -774,13 +785,14 @@ public class MVStore {
      *
      * @return the new version (incremented if there were changes)
      */
-    public synchronized long store() {
+    private synchronized long commitAndSave() {
         if (closed) {
             return currentVersion;
         }
         if (fileStore == null) {
             throw DataUtils.newIllegalStateException(
-                    DataUtils.ERROR_WRITING_FAILED, "This is an in-memory store");
+                    DataUtils.ERROR_WRITING_FAILED,
+                    "This is an in-memory store");
         }
         if (currentStoreVersion >= 0) {
             // store is possibly called within store, if the meta map changed
@@ -811,7 +823,7 @@ public class MVStore {
         long version = ++currentVersion;
         setWriteVersion(version);
         long time = getTime();
-        lastStoreTime = time;
+        lastCommitTime = time;
         retainChunk = null;
 
         // the last chunk was not completely correct in the last store()
@@ -903,14 +915,6 @@ public class MVStore {
         }
         boolean storeAtEndOfFile = filePos + length >= end;
 
-//        try {
-//            Thread.sleep(10);
-//        } catch (InterruptedException e) {
-//        ; int todo;
-//            // TODO Auto-generated catch block
-//            e.printStackTrace();
-//        }
-
         c.start = filePos;
         c.length = chunkLength;
         c.metaRootPos = metaRoot.getPos();
@@ -944,8 +948,10 @@ public class MVStore {
         }
         metaRoot.writeEnd();
 
-        // some pages might have been changed in the meantime (in the newest version)
-        unsavedPageCount = Math.max(0, unsavedPageCount - currentUnsavedPageCount);
+        // some pages might have been changed in the meantime (in the newest
+        // version)
+        unsavedPageCount = Math.max(0, unsavedPageCount
+                - currentUnsavedPageCount);
 
         metaChanged = false;
         lastStoredVersion = storeVersion;
@@ -1098,7 +1104,8 @@ public class MVStore {
         long size = 2 * BLOCK_SIZE;
         for (Chunk c : chunks.values()) {
             long x = c.start + c.length;
-            size = Math.max(size, MathUtils.roundUpLong(x, BLOCK_SIZE) + BLOCK_SIZE);
+            size = Math.max(size, MathUtils.roundUpLong(x, BLOCK_SIZE)
+                    + BLOCK_SIZE);
         }
         return size;
     }
@@ -1109,8 +1116,6 @@ public class MVStore {
      * @return if there are any changes
      */
     public boolean hasUnsavedChanges() {
-        // TODO maybe private; rename to hasUncommittedChanges
-        
         checkOpen();
         if (metaChanged) {
             return true;
@@ -1160,7 +1165,8 @@ public class MVStore {
             chunks.remove(c.id);
             markMetaChanged();
             meta.remove("chunk." + c.id);
-            int length = MathUtils.roundUpInt(c.length, BLOCK_SIZE) + BLOCK_SIZE;
+            int length = MathUtils.roundUpInt(c.length, BLOCK_SIZE)
+                    + BLOCK_SIZE;
             fileStore.free(c.start, length);
         }
         if (fileStore.getFillRate() == 100) {
@@ -1175,7 +1181,8 @@ public class MVStore {
         }
         for (Chunk c : move) {
             WriteBuffer buff = getWriteBuffer();
-            int length = MathUtils.roundUpInt(c.length, BLOCK_SIZE) + BLOCK_SIZE;
+            int length = MathUtils.roundUpInt(c.length, BLOCK_SIZE)
+                    + BLOCK_SIZE;
             buff.limit(length);
             ByteBuffer buff2 = fileStore.readFully(c.start, length);
             buff.put(buff2);
@@ -1200,7 +1207,7 @@ public class MVStore {
 
         // update the metadata (store at the end of the file)
         reuseSpace = false;
-        store();
+        commitAndSave();
 
         sync();
 
@@ -1213,7 +1220,8 @@ public class MVStore {
                 continue;
             }
             WriteBuffer buff = getWriteBuffer();
-            int length = MathUtils.roundUpInt(c.length, BLOCK_SIZE) + BLOCK_SIZE;
+            int length = MathUtils.roundUpInt(c.length, BLOCK_SIZE)
+                    + BLOCK_SIZE;
             buff.limit(length);
             ByteBuffer buff2 = fileStore.readFully(c.start, length);
             buff.put(buff2);
@@ -1235,7 +1243,7 @@ public class MVStore {
         }
 
         // update the metadata (within the file)
-        store();
+        commitAndSave();
         sync();
         shrinkFileIfPossible(0);
 
@@ -1309,7 +1317,8 @@ public class MVStore {
         Collections.sort(old, new Comparator<Chunk>() {
             @Override
             public int compare(Chunk o1, Chunk o2) {
-                return new Integer(o1.collectPriority).compareTo(o2.collectPriority);
+                return new Integer(o1.collectPriority)
+                        .compareTo(o2.collectPriority);
             }
         });
 
@@ -1341,7 +1350,7 @@ public class MVStore {
             copyLive(c, old);
         }
 
-        store();
+        commitAndSave();
         return true;
     }
 
@@ -1413,7 +1422,8 @@ public class MVStore {
             filePos += DataUtils.getPageOffset(pos);
             if (filePos < 0) {
                 throw DataUtils.newIllegalStateException(
-                        DataUtils.ERROR_FILE_CORRUPT, "Negative position {0}", filePos);
+                        DataUtils.ERROR_FILE_CORRUPT,
+                        "Negative position {0}", filePos);
             }
             p = Page.read(fileStore, map, pos, filePos, fileStore.size());
             if (cache != null) {
@@ -1460,11 +1470,13 @@ public class MVStore {
         registerFreePage(version, c.id, DataUtils.getPageMaxLength(pos), 1);
     }
 
-    private void registerFreePage(long version, int chunkId, long maxLengthLive, int pageCount) {
+    private void registerFreePage(long version, int chunkId,
+            long maxLengthLive, int pageCount) {
         HashMap<Integer, Chunk> freed = freedPageSpace.get(version);
         if (freed == null) {
             freed = New.hashMap();
-            HashMap<Integer, Chunk> f2 = freedPageSpace.putIfAbsent(version, freed);
+            HashMap<Integer, Chunk> f2 = freedPageSpace.putIfAbsent(version,
+                    freed);
             if (f2 != null) {
                 freed = f2;
             }
@@ -1541,13 +1553,13 @@ public class MVStore {
     }
 
     /**
-     * Which version to retain in memory. If not set, all versions back to the
-     * last stored version are retained.
+     * How many versions to retain for in-memory stores. If not set, 5 versions
+     * are retained.
      *
-     * @param retainVersion the oldest version to retain
+     * @param count the number of versions to keep
      */
-    public void setRetainVersion(long retainVersion) {
-        this.retainVersion = retainVersion;
+    public void setVersionsToKeep(int count) {
+        this.versionsToKeep = count;
     }
 
     /**
@@ -1555,13 +1567,8 @@ public class MVStore {
      *
      * @return the version
      */
-    public long getRetainVersion() {
-        long v = retainVersion;
-        long storeVersion = currentStoreVersion;
-        if (storeVersion > -1) {
-            v = Math.min(v, storeVersion);
-        }
-        return v;
+    public long getVersionsToKeep() {
+        return versionsToKeep;
     }
 
     /**
@@ -1570,8 +1577,11 @@ public class MVStore {
      *
      * @return the version
      */
-    long getRetainOrStoreVersion() {
-        long v = retainVersion;
+    long getOldestVersionToKeep() {
+        long v = currentVersion;
+        if (fileStore == null) {
+            return v - versionsToKeep;
+        }
         long storeVersion = currentStoreVersion;
         if (storeVersion > -1) {
             v = Math.min(v, storeVersion);
@@ -1618,34 +1628,13 @@ public class MVStore {
         return true;
     }
 
-    /**
-     * Get the estimated number of unsaved pages. The returned value is not
-     * accurate, specially after rollbacks, but can be used to estimate the
-     * memory usage for unsaved data.
-     *
-     * @return the number of unsaved pages
-     */
-    public int getUnsavedPageCount() {
-        return unsavedPageCount;
-    }
-
-    /**
-     * Get the maximum number of unsaved pages. If this number is exceeded, the
-     * unsaved changes are stored to disk.
-     * 
-     * @return the number of maximum unsaved pages
-     */
-    public int getUnsavedPageCountMax() {
-        return unsavedPageCountMax;
-    }
-
     /**
      * Increment the number of unsaved pages.
      */
     void registerUnsavedPage() {
         int count = ++unsavedPageCount;
-        if (count > unsavedPageCountMax && unsavedPageCountMax > 0) {
-            storeNeeded = true;
+        if (count > autoCommitPageCount && autoCommitPageCount > 0) {
+            saveNeeded = true;
         }
     }
 
@@ -1653,9 +1642,9 @@ public class MVStore {
      * This method is called before writing to a map.
      */
     void beforeWrite() {
-        if (storeNeeded) {
-            storeNeeded = false;
-            store();
+        if (saveNeeded) {
+            saveNeeded = false;
+            commitAndSave();
         }
     }
 
@@ -1682,13 +1671,12 @@ public class MVStore {
         markMetaChanged();
         meta.put("setting.storeVersion", Integer.toString(version));
     }
-    
+
     /**
-     * Revert to the beginning of the current version.
+     * Revert to the beginning of the current version, reverting all uncommitted
+     * changes.
      */
     public void rollback() {
-        // TODO document and test
-        
         rollbackTo(currentVersion);
     }
 
@@ -1841,11 +1829,11 @@ public class MVStore {
 
     private void checkOpen() {
         if (closed) {
-            throw DataUtils.newIllegalStateException(
-                    DataUtils.ERROR_CLOSED, "This store is closed");
+            throw DataUtils.newIllegalStateException(DataUtils.ERROR_CLOSED,
+                    "This store is closed");
         }
     }
-    
+
     /**
      * Rename a map.
      *
@@ -1901,25 +1889,25 @@ public class MVStore {
     }
 
     /**
-     * Store all unsaved changes, if there are any that are committed.
+     * Commit and save all changes, if there are any.
      */
-    void storeInBackground() {
+    void commitInBackground() {
         if (unsavedPageCount == 0 || closed) {
             return;
         }
 
         // could also store when there are many unsaved pages,
         // but according to a test it doesn't really help
-        
+
         long time = getTime();
-        if (time <= lastStoreTime + writeDelay) {
+        if (time <= lastCommitTime + autoCommitDelay) {
             return;
         }
         if (!hasUnsavedChanges()) {
             return;
         }
         try {
-            store();
+            commitAndSave();
         } catch (Exception e) {
             if (backgroundExceptionHandler != null) {
                 backgroundExceptionHandler.uncaughtException(null, e);
@@ -1959,25 +1947,21 @@ public class MVStore {
     }
 
     /**
-     * Set the maximum delay in milliseconds to commit changes.
+     * Set the maximum delay in milliseconds to auto-commit changes.
      * <p>
-     * The default is 1000, meaning changes are committed after at
-     * most one second.
+     * To disable auto-commit, set the value to 0. In this case, changes are
+     * only committed when explicitly calling commit.
      * <p>
-     * When the value is set to -1, changes are only written when
-     * calling the store method. When the value is set to 0, committed
-     * changes are immediately written on a commit, but please note this
-     * decreases performance and does still not guarantee the disk will
-     * actually write the data.
+     * The default is 1000, meaning all changes are committed after at most one
+     * second.
      *
      * @param millis the maximum delay
      */
-    public void setWriteDelay(int millis) {
-        // TODO rename to commitDelay
-        if (writeDelay == millis) {
+    public void setAutoCommitDelay(int millis) {
+        if (autoCommitDelay == millis) {
             return;
         }
-        writeDelay = millis;
+        autoCommitDelay = millis;
         if (fileStore == null) {
             return;
         }
@@ -1991,8 +1975,36 @@ public class MVStore {
         }
     }
 
-    public int getWriteDelay() {
-        return writeDelay;
+    /**
+     * Get the auto-commit delay.
+     *
+     * @return the delay in milliseconds, or 0 if auto-commit is disabled.
+     */
+    public int getAutoCommitDelay() {
+        return autoCommitDelay;
+    }
+
+    /**
+     * Get the maximum number of unsaved pages. If this number is exceeded,
+     * unsaved changes are stored to disk.
+     *
+     * @return the number of maximum unsaved pages
+     */
+    public int getAutoCommitPageCount() {
+        return autoCommitPageCount;
+    }
+
+    /**
+     * Get the estimated number of unsaved pages. If the value exceeds the
+     * auto-commit page count, the changes are committed.
+     * <p>
+     * The returned value may not be completely accurate, but can be used to
+     * estimate the memory usage for unsaved data.
+     *
+     * @return the number of unsaved pages
+     */
+    public int getUnsavedPageCount() {
+        return unsavedPageCount;
     }
 
     /**
@@ -2000,9 +2012,9 @@ public class MVStore {
      */
     private static class BackgroundWriterThread extends Thread {
 
+        public final Object sync = new Object();
         private final MVStore store;
         private final int sleep;
-        public final Object sync = new Object();
 
         BackgroundWriterThread(MVStore store, int sleep, String fileStoreName) {
             super("MVStore background writer " + fileStoreName);
@@ -2025,7 +2037,7 @@ public class MVStore {
                         continue;
                     }
                 }
-                store.storeInBackground();
+                store.commitInBackground();
             }
         }
 
@@ -2043,6 +2055,38 @@ public class MVStore {
             return this;
         }
 
+        /**
+         * Disable auto-commit, by setting the auto-commit delay and auto-commit
+         * buffer size to 0.
+         *
+         * @return this
+         */
+        public Builder autoCommitDisabled() {
+            // we have a separate config option so that
+            // no thread is started if the write delay is 0
+            // (if we only had a setter in the MVStore,
+            // the thread would need to be started in any case)
+            set("autoCommitBufferSize", 0);
+            return set("autoCommitDelay", 0);
+        }
+
+        /**
+         * Set the size of the write buffer, in MB (for file-based stores).
+         * Unless auto-commit is disabled, changes are automatically saved if
+         * there are more than this amount of changes.
+         * <p>
+         * The default is 4 MB.
+         * <p>
+         * When the value is set to 0 or lower, data is not automatically
+         * stored.
+         *
+         * @param mb the write buffer size, in megabytes
+         * @return this
+         */
+        public Builder autoCommitBufferSize(int mb) {
+            return set("autoCommitBufferSize", mb);
+        }
+
         /**
          * Use the following file name. If the file does not exist, it is
          * automatically created. The parent directory already must exist.
@@ -2076,8 +2120,8 @@ public class MVStore {
          * If this option is not used, the file is locked exclusively.
          * <p>
          * Please note a store may only be opened once in every JVM (no matter
-         * whether it is opened in read-only or read-write mode), because each file
-         * may be locked only once in a process.
+         * whether it is opened in read-only or read-write mode), because each
+         * file may be locked only once in a process.
          *
          * @return this
          */
@@ -2110,23 +2154,6 @@ public class MVStore {
             return set("compress", 1);
         }
 
-        /**
-         * Set the size of the write buffer, in MB (for file-based stores).
-         * Unless auto-commit is disabled, changes are automatically stored if
-         * the buffer grows larger than this.
-         * <p>
-         * The default is 4 MB.
-         * <p>
-         * When the value is set to 0 or lower, data is never automatically
-         * stored.
-         *
-         * @param mb the write buffer size, in megabytes
-         * @return this
-         */
-        public Builder writeBufferSize(int mb) {
-            return set("writeBufferSize", mb);
-        }
-
         /**
          * Set the amount of memory a page should contain at most, in bytes,
          * before it is split. The default is 6 KB. This is not a limit in the
@@ -2141,8 +2168,8 @@ public class MVStore {
         }
 
         /**
-         * Set the listener to be used for exceptions that occur in the background
-         * thread.
+         * Set the listener to be used for exceptions that occur when writing in
+         * the background thread.
          *
          * @param exceptionHandler the handler
          * @return this
@@ -2162,20 +2189,6 @@ public class MVStore {
             return set("fileStore", store);
         }
 
-        /**
-         * Set the initial write delay.
-         *
-         * @param writeDelay the write delay
-         * @return this
-         */
-        public Builder writeDelay(int writeDelay) {
-            // we have a separate config option so that
-            // no thread is started if the write delay is 0
-            // (if we only had a setter in the MVStore,
-            // the thread would need to be started in any case)
-            return set("writeDelay", writeDelay);
-        }
-
         /**
          * Open the store.
          *

h2/src/main/org/h2/mvstore/db/MVSecondaryIndex.java

@@ -96,7 +96,7 @@ public class MVSecondaryIndex extends BaseIndex {
             }
         }
         try {
-            map.put(array, ValueLong.get(0));
+            map.put(array, ValueNull.INSTANCE);
         } catch (IllegalStateException e) {
             throw DbException.get(ErrorCode.CONCURRENT_UPDATE_1, table.getName());
         }

h2/src/main/org/h2/mvstore/db/MVSpatialIndex.java

@@ -54,10 +54,11 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex {
     private final String mapName;
     private TransactionMap<SpatialKey, Value> dataMap;
     private MVRTreeMap<VersionedValue> spatialMap;
-    
+
     /**
      * Constructor.
      *
+     * @param db the database
      * @param table the table instance
      * @param id the index id
      * @param indexName the index name
@@ -66,7 +67,7 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex {
      */
     public MVSpatialIndex(
             Database db, MVTable table, int id, String indexName,
-            IndexColumn[] columns, IndexType indexType) {            
+            IndexColumn[] columns, IndexType indexType) {
         if (columns.length != 1) {
             throw DbException.getUnsupportedException("Can only index one column");
         }
@@ -92,7 +93,7 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex {
         mapName = "index." + getId();
         ValueDataType vt = new ValueDataType(null, null, null);
         VersionedValueType valueType = new VersionedValueType(vt);
-        MVRTreeMap.Builder<VersionedValue> mapBuilder = 
+        MVRTreeMap.Builder<VersionedValue> mapBuilder =
                 new MVRTreeMap.Builder<VersionedValue>().
                 valueType(valueType);
         spatialMap = db.getMvStore().getStore().openMap(mapName, mapBuilder);
@@ -144,7 +145,7 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex {
             }
         }
     }
-    
+
     private SpatialKey getKey(SearchRow r) {
         if (r == null) {
             return null;
@@ -171,7 +172,7 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex {
             throw DbException.get(ErrorCode.CONCURRENT_UPDATE_1, table.getName());
         }
     }
-    
+
     @Override
     public Cursor find(TableFilter filter, SearchRow first, SearchRow last) {
         return find(filter.getSession());
@@ -200,7 +201,7 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex {
         Iterator<SpatialKey> it = map.wrapIterator(cursor, false);
         return new MVStoreCursor(session, it);
     }
-    
+
     private SpatialKey getEnvelope(SearchRow row) {
         Value v = row.getValue(columnIds[0]);
         Geometry g = ((ValueGeometry) v.convertTo(Value.GEOMETRY)).getGeometry();
@@ -232,7 +233,7 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex {
     public double getCost(Session session, int[] masks, TableFilter filter, SortOrder sortOrder) {
         return getCostRangeIndex(masks, table.getRowCountApproximation(), filter, sortOrder);
     }
-    
+
     @Override
     protected long getCostRangeIndex(int[] masks, long rowCount, TableFilter filter, SortOrder sortOrder) {
         rowCount += Constants.COST_ROW_OFFSET;

h2/src/main/org/h2/mvstore/db/MVTable.java

@@ -399,7 +399,7 @@ public class MVTable extends TableBase {
                     indexName, primaryIndex, indexType);
         } else if (indexType.isSpatial()) {
             index = new MVSpatialIndex(session.getDatabase(),
-                    this, indexId, 
+                    this, indexId,
                     indexName, cols, indexType);
         } else {
             index = new MVSecondaryIndex(session.getDatabase(),

h2/src/main/org/h2/mvstore/db/MVTableEngine.java

@@ -168,13 +168,13 @@ public class MVTableEngine implements TableEngine {
         /**
          * Store all pending changes.
          */
-        public void store() {
+        public void flush() {
             FileStore s = store.getFileStore();
             if (s == null || s.isReadOnly()) {
                 return;
             }
             if (!store.compact(50)) {
-                store.store();
+                store.commit();
             }
         }
 
@@ -213,9 +213,7 @@ public class MVTableEngine implements TableEngine {
             Transaction t = session.getTransaction();
             t.setName(transactionName);
             t.prepare();
-            if (store.getFileStore() != null) {
-                store.store();
-            }
+            store.commit();
         }
 
         public ArrayList<InDoubtTransaction> getInDoubtTransactions() {
@@ -245,7 +243,7 @@ public class MVTableEngine implements TableEngine {
          * Force the changes to disk.
          */
         public void sync() {
-            store();
+            flush();
             store.sync();
         }
 
@@ -316,9 +314,7 @@ public class MVTableEngine implements TableEngine {
             } else {
                 transaction.rollback();
             }
-            if (store.getFileStore() != null) {
-                store.store();
-            }
+            store.commit();
             this.state = state;
         }
 

h2/src/main/org/h2/mvstore/db/TransactionStore.java

@@ -170,9 +170,7 @@ public class TransactionStore {
     public synchronized void close() {
         // to avoid losing transaction ids
         settings.put(LAST_TRANSACTION_ID, "" + lastTransactionId);
-        if (store.getFileStore() != null) {
-            store.store();
-        }
+        store.commit();
     }
 
     /**
@@ -192,9 +190,7 @@ public class TransactionStore {
 
     private void commitIfNeeded() {
         if (store.getUnsavedPageCount() > MAX_UNSAVED_PAGES) {
-            if (store.getFileStore() != null) {
-                store.store();
-            }
+            store.commit();
         }
     }
 
@@ -354,10 +350,8 @@ public class TransactionStore {
         if (t.getId() == firstOpenTransaction) {
             firstOpenTransaction = -1;
         }
-        if (store.getWriteDelay() == 0) {
-            if (store.getFileStore() != null) {
-                store.store();
-            }
+        if (store.getAutoCommitDelay() == 0) {
+            store.commit();
             return;
         }
         // to avoid having to store the transaction log,
@@ -365,10 +359,10 @@ public class TransactionStore {
         // and if there have been many changes, store them now
         if (undoLog.isEmpty()) {
             int unsaved = store.getUnsavedPageCount();
-            int max = store.getUnsavedPageCountMax();
+            int max = store.getAutoCommitPageCount();
             // save at 3/4 capacity
             if (unsaved * 4 > max * 3) {
-                store.store();
+                store.commit();
             }
         }
     }
@@ -658,7 +652,15 @@ public class TransactionStore {
             int mapId = map.getId();
             return new TransactionMap<K, V>(this, map, mapId);
         }
-        
+
+        /**
+         * Open the transactional version of the given map.
+         *
+         * @param <K> the key type
+         * @param <V> the value type
+         * @param map the base map
+         * @return the transactional map
+         */
         public <K, V> TransactionMap<K, V> openMap(MVMap<K, VersionedValue> map) {
             checkNotClosed();
             int mapId = map.getId();
@@ -726,9 +728,11 @@ public class TransactionStore {
                         DataUtils.ERROR_CLOSED, "Transaction is closed");
             }
         }
-        
+
         /**
          * Remove the map.
+         *
+         * @param map the map
          */
         public <K, V> void removeMap(TransactionMap<K, V> map) {
             store.store.removeMap(map.map);
@@ -1258,7 +1262,7 @@ public class TransactionStore {
                 }
             };
         }
-        
+
         public Transaction getTransaction() {
             return transaction;
         }

h2/src/test/org/h2/test/store/TestConcurrent.java

@@ -56,33 +56,32 @@ public class TestConcurrent extends TestMVStore {
         testConcurrentWrite();
         testConcurrentRead();
     }
-    
+
     private void testConcurrentFree() throws InterruptedException {
         String fileName = "memFS:testConcurrentFree.h3";
         for (int test = 0; test < 10; test++) {
             FileUtils.delete(fileName);
             final MVStore s1 = new MVStore.Builder().
-                    fileName(fileName).writeDelay(-1).open();
+                    fileName(fileName).autoCommitDisabled().open();
             s1.setRetentionTime(0);
             final int count = 200;
             for (int i = 0; i < count; i++) {
                 MVMap<Integer, Integer> m = s1.openMap("d" + i);
                 m.put(1, 1);
                 if (i % 2 == 0) {
-                    s1.store();
+                    s1.commit();
                 }
             }
-            s1.store();
             s1.close();
             final MVStore s = new MVStore.Builder().
-                    fileName(fileName).writeDelay(-1).open();
+                    fileName(fileName).autoCommitDisabled().open();
             s.setRetentionTime(0);
             final ArrayList<MVMap<Integer, Integer>> list = New.arrayList();
             for (int i = 0; i < count; i++) {
                 MVMap<Integer, Integer> m = s.openMap("d" + i);
                 list.add(m);
             }
-            
+
             final AtomicInteger counter = new AtomicInteger();
             Task task = new Task() {
                 @Override
@@ -113,8 +112,8 @@ public class TestConcurrent extends TestMVStore {
                 }
             }
             task.get();
-            s.store();
-            
+            s.commit();
+
             MVMap<String, String> meta = s.getMetaMap();
             int chunkCount = 0;
             for (String k : meta.keyList()) {
@@ -142,7 +141,7 @@ public class TestConcurrent extends TestMVStore {
             public void call() throws Exception {
                 while (!stop) {
                     counter.incrementAndGet();
-                    s.store();
+                    s.commit();
                 }
             }
         };
@@ -172,7 +171,7 @@ public class TestConcurrent extends TestMVStore {
                 public void call() throws Exception {
                     while (!stop) {
                         s.setStoreVersion(counter.incrementAndGet());
-                        s.store();
+                        s.commit();
                     }
                 }
             };
@@ -270,9 +269,9 @@ public class TestConcurrent extends TestMVStore {
                     for (int i = 0; i < 10; i++) {
                         map.put(i, new byte[100 * r.nextInt(100)]);
                     }
-                    s.store();
+                    s.commit();
                     map.clear();
-                    s.store();
+                    s.commit();
                     long len = s.getFileStore().size();
                     if (len > 1024 * 1024) {
                         // slow down writing a lot
@@ -322,6 +321,7 @@ public class TestConcurrent extends TestMVStore {
 
     private void testConcurrentIterate() {
         MVStore s = new MVStore.Builder().pageSplitSize(3).open();
+        s.setVersionsToKeep(100);
         final MVMap<Integer, Integer> map = s.openMap("test");
         final int len = 10;
         final Random r = new Random();
@@ -343,7 +343,6 @@ public class TestConcurrent extends TestMVStore {
             Iterator<Integer> it = map.keyIterator(r.nextInt(len));
             long old = s.getCurrentVersion();
             s.commit();
-            s.setRetainVersion(old - 100);
             while (map.getVersion() == old) {
                 Thread.yield();
             }

h2/src/test/org/h2/test/store/TestKillProcessWhileWriting.java

@@ -84,9 +84,8 @@ public class TestKillProcessWhileWriting extends TestBase {
         s = new MVStore.Builder().
                 fileName(fileName).
                 pageSplitSize(50).
-                writeDelay(0).
+                autoCommitDisabled().
                 open();
-        s.setWriteDelay(0);
         m = s.openMap("data");
         Random r = new Random(seed);
         int op = 0;
@@ -107,7 +106,7 @@ public class TestKillProcessWhileWriting extends TestBase {
                     m.remove(k);
                     break;
                 case 6:
-                    s.store();
+                    s.commit();
                     break;
                 case 7:
                     s.compact(80);
@@ -120,12 +119,12 @@ public class TestKillProcessWhileWriting extends TestBase {
                     s = new MVStore.Builder().
                             fileName(fileName).
                             pageSplitSize(50).
-                            writeDelay(0).open();
+                            autoCommitDisabled().
+                            open();
                     m = s.openMap("data");
                     break;
                 }
             }
-            s.store();
             s.close();
             return 0;
         } catch (Exception e) {

h2/src/test/org/h2/test/store/TestMVRTree.java

@@ -54,7 +54,7 @@ public class TestMVRTree extends TestMVStore {
         testRandom();
         testRandomFind();
     }
-    
+
     private void testSpatialKey() {
         SpatialKey a0 = new SpatialKey(0, 1, 2, 3, 4);
         SpatialKey a1 = new SpatialKey(0, 1, 2, 3, 4);
@@ -119,7 +119,7 @@ public class TestMVRTree extends TestMVStore {
             SpatialKey k = new SpatialKey(i, x - p, x + p, y - p, y + p);
             r.add(k, "" + i);
             if (i > 0 && (i % len / 10) == 0) {
-                s.store();
+                s.commit();
             }
             if (i > 0 && (i % 10000) == 0) {
                 render(r, getBaseDir() + "/test.png");
@@ -127,7 +127,6 @@ public class TestMVRTree extends TestMVStore {
         }
         // System.out.println(prof.getTop(5));
         // System.out.println("add: " + (System.currentTimeMillis() - t));
-        s.store();
         s.close();
         s = openStore(fileName);
         r = s.openMap("data",

h2/src/test/org/h2/test/store/TestMVStore.java

@@ -48,6 +48,8 @@ public class TestMVStore extends TestBase {
     public void test() throws Exception {
         FileUtils.deleteRecursive(getBaseDir(), true);
         FileUtils.createDirectories(getBaseDir());
+        testRollback();
+        testVersionsToKeep();
         testRemoveMap();
         testIsEmpty();
         testOffHeapStorage();
@@ -97,6 +99,26 @@ public class TestMVStore extends TestBase {
         testLargerThan2G();
     }
 
+    private void testVersionsToKeep() throws Exception {
+        MVStore s = new MVStore.Builder().open();
+        MVMap<Integer, Integer> map;
+        map = s.openMap("data");
+        for (int i = 0; i < 20; i++) {
+            long version = s.getCurrentVersion();
+            map.put(i, i);
+            s.commit();
+            if (version >= 6) {
+                map.openVersion(version - 6);
+                try {
+                    map.openVersion(version - 7);
+                    fail();
+                } catch (IllegalArgumentException e) {
+                    // expected
+                }
+            }
+        }
+    }
+
     private void testRemoveMap() throws Exception {
         String fileName = getBaseDir() + "/testCloseMap.h3";
         FileUtils.delete(fileName);
@@ -108,15 +130,14 @@ public class TestMVStore extends TestBase {
         map = s.openMap("data");
         map.put(1, 1);
         assertEquals(1, map.get(1).intValue());
-        s.store();
+        s.commit();
 
         s.removeMap(map);
-        s.store();
+        s.commit();
 
         map = s.openMap("data");
         assertTrue(map.isEmpty());
         map.put(2, 2);
-        s.store();
 
         s.close();
     }
@@ -145,7 +166,7 @@ public class TestMVStore extends TestBase {
         Map<Integer, String> map = s.openMap("data");
         for (int i = 0; i < 1000; i++) {
             map.put(i, "Hello " + i);
-            s.store();
+            s.commit();
         }
         assertTrue(1000 < offHeap.getWriteCount());
         s.close();
@@ -173,7 +194,6 @@ public class TestMVStore extends TestBase {
         header.put("format", "2");
         MVMap<Integer, String> m = s.openMap("data");
         m.put(0, "Hello World");
-        s.store();
         s.close();
 
         try {
@@ -218,12 +238,12 @@ public class TestMVStore extends TestBase {
         for (int i = 0; i < 10; i++) {
             m = s.openMap("data" + i);
             m.put(0, "Hello World");
-            s.store();
+            s.commit();
         }
         for (int i = 0; i < 10; i += 2) {
             m = s.openMap("data" + i);
             s.removeMap(m);
-            s.store();
+            s.commit();
         }
         long sizeOld = s.getFileStore().size();
         s.compactMoveChunks();
@@ -248,7 +268,7 @@ public class TestMVStore extends TestBase {
 
                 }).
                 open();
-        s.setWriteDelay(2);
+        s.setAutoCommitDelay(2);
         MVMap<Integer, String> m;
         m = s.openMap("data");
         s.getFileStore().getFile().close();
@@ -313,7 +333,7 @@ public class TestMVStore extends TestBase {
         for (int bs = 0; bs <= 1; bs++) {
             s = new MVStore.Builder().
                     fileName(fileName).
-                    writeBufferSize(bs).
+                    autoCommitBufferSize(bs).
                     open();
             m = s.openMap("data");
             for (int i = 0; i < len; i++) {
@@ -332,7 +352,7 @@ public class TestMVStore extends TestBase {
         assertTrue(m.containsKey(1));
 
         m.put(-1, data);
-        s.store();
+        s.commit();
         m.put(-2, data);
         s.close();
 
@@ -354,15 +374,15 @@ public class TestMVStore extends TestBase {
 
         FileUtils.delete(fileName);
         s = new MVStore.Builder().
+                autoCommitDisabled().
                 fileName(fileName).open();
-        s.setWriteDelay(0);
         m = s.openMap("data");
         m.put(1, "1");
         s.commit();
         s.close();
         s = new MVStore.Builder().
+                autoCommitDisabled().
                 fileName(fileName).open();
-        s.setWriteDelay(0);
         m = s.openMap("data");
         assertEquals(1, m.size());
         s.close();
@@ -371,10 +391,10 @@ public class TestMVStore extends TestBase {
         s = new MVStore.Builder().
                 fileName(fileName).
                 open();
-        s.setWriteDelay(1);
+        s.setAutoCommitDelay(1);
         m = s.openMap("data");
         m.put(1, "Hello");
-        s.store();
+        s.commit();
         long v = s.getCurrentVersion();
         m.put(2, "World.");
         Thread.sleep(5);
@@ -383,12 +403,11 @@ public class TestMVStore extends TestBase {
         s = new MVStore.Builder().
                 fileName(fileName).
                 open();
-        s.setWriteDelay(1);
+        s.setAutoCommitDelay(1);
         m = s.openMap("data");
         assertEquals("World.", m.get(2));
         m.put(2, "World");
         s.commit();
-        s.store();
         v = s.getCurrentVersion();
         m.put(3, "!");
 
@@ -433,7 +452,6 @@ public class TestMVStore extends TestBase {
         m = s.openMap("test");
         m.put(1, "Hello");
         assertEquals("Hello", m.get(1));
-        s.store();
         s.close();
 
         passwordChars = "008".toCharArray();
@@ -485,7 +503,6 @@ public class TestMVStore extends TestBase {
         int format = Integer.parseInt(header.get("format"));
         assertEquals(1, format);
         header.put("format", Integer.toString(format + 1));
-        s.store();
         s.close();
         try {
             openStore(fileName).close();
@@ -503,9 +520,8 @@ public class TestMVStore extends TestBase {
         MVStore s = openStore(fileName);
         MVMap<Integer, Integer> m = s.openMap("test");
         m.put(1, 1);
-        s.store();
+        s.commit();
         s.removeMap(m);
-        s.store();
         s.close();
         s = openStore(fileName);
         m = s.openMap("test");
@@ -548,17 +564,16 @@ public class TestMVStore extends TestBase {
         MVMap<Integer, String> map;
         s = new MVStore.Builder().
                 fileName(fileName).
-                writeDelay(-1).
+                autoCommitDisabled().
                 compressData().open();
         map = s.openMap("test");
         // add 10 MB of data
         for (int i = 0; i < 1024; i++) {
             map.put(i, new String(new char[10240]));
         }
-        s.store();
         s.close();
         int[] expectedReadsForCacheSize = {
-                3405, 2590, 1924, 1440, 1108, 956, 918
+                3413, 2590, 1924, 1440, 1112, 956, 918
         };
         for (int cacheSize = 0; cacheSize <= 6; cacheSize += 4) {
             s = new MVStore.Builder().
@@ -613,7 +628,6 @@ public class TestMVStore extends TestBase {
         s.getStoreHeader().put("test", "123");
         MVMap<Integer, Integer> map = s.openMap("test");
         map.put(10, 100);
-        s.store();
         s.close();
         s = openStore(fileName);
         assertEquals("123", s.getStoreHeader().get("test"));
@@ -630,14 +644,13 @@ public class TestMVStore extends TestBase {
         for (int i = 0; i < 10; i++) {
             map = s.openMap("test" + i);
             map.put(0, new byte[1000]);
-            s.store();
+            s.commit();
         }
         FileStore fs = s.getFileStore();
         long size = fs.getFile().size();
         for (int i = 0; i < 10; i++) {
             map = s.openMap("test" + i);
             s.removeMap(map);
-            s.store();
             s.commit();
             s.compact(100);
             if (fs.getFile().size() <= size) {
@@ -818,14 +831,13 @@ public class TestMVStore extends TestBase {
         assertEquals(0, s.getCurrentVersion());
         assertEquals(0, s.getStoreVersion());
         s.setStoreVersion(0);
-        s.store();
+        s.commit();
         s.setStoreVersion(1);
         s.closeImmediately();
         s = MVStore.open(fileName);
         assertEquals(1, s.getCurrentVersion());
         assertEquals(0, s.getStoreVersion());
         s.setStoreVersion(1);
-        s.store();
         s.close();
         s = MVStore.open(fileName);
         assertEquals(2, s.getCurrentVersion());
@@ -866,7 +878,6 @@ public class TestMVStore extends TestBase {
         map.put(1,  "Hello");
         map.put("2", 200);
         map.put(new Object[1], new Object[]{1, "2"});
-        s.store();
         s.close();
 
         s = new MVStore.Builder().fileName(fileName).open();
@@ -958,7 +969,7 @@ public class TestMVStore extends TestBase {
                 for (int i = 0; i < 3; i++) {
                     Integer x = m.get("value");
                     m.put("value", x == null ? 0 : x + 1);
-                    s.store();
+                    s.commit();
                 }
                 s.close();
             }
@@ -972,7 +983,7 @@ public class TestMVStore extends TestBase {
         for (int op = 0; op <= 1; op++) {
             for (int i = 0; i < 5; i++) {
                 s = openStore(null);
-                s.setRetainVersion(0);
+                s.setVersionsToKeep(Integer.MAX_VALUE);
                 MVMap<String, String> m;
                 m = s.openMap("data");
                 for (int j = 0; j < 5; j++) {
@@ -1021,7 +1032,7 @@ public class TestMVStore extends TestBase {
         assertEquals("World", mOld.get("2"));
         assertTrue(mOld.isReadOnly());
         s.getCurrentVersion();
-        long old3 = s.store();
+        long old3 = s.commit();
 
         // the old version is still available
         assertEquals("Hello", mOld.get("1"));
@@ -1033,7 +1044,6 @@ public class TestMVStore extends TestBase {
 
         m.put("1",  "Hi");
         assertEquals("Welt", m.remove("2"));
-        s.store();
         s.close();
 
         s = openStore(fileName);
@@ -1064,14 +1074,12 @@ public class TestMVStore extends TestBase {
         for (int i = 0; i < 1000; i++) {
             m.put(i, "Hello World");
         }
-        s.store();
         s.close();
         long len = FileUtils.size(fileName);
         s = openStore(fileName);
         s.setRetentionTime(0);
         m = s.openMap("data");
         m.clear();
-        s.store();
         s.compact(100);
         s.close();
         long len2 = FileUtils.size(fileName);
@@ -1091,7 +1099,7 @@ public class TestMVStore extends TestBase {
         }
         assertEquals(1000, m.size());
         assertEquals(285, s.getUnsavedPageCount());
-        s.store();
+        s.commit();
         assertEquals(2, s.getFileStore().getWriteCount());
         s.close();
 
@@ -1099,13 +1107,27 @@ public class TestMVStore extends TestBase {
         m = s.openMap("data");
         m.clear();
         assertEquals(0, m.size());
-        s.store();
+        s.commit();
         // ensure only nodes are read, but not leaves
         assertEquals(42, s.getFileStore().getReadCount());
         assertEquals(1, s.getFileStore().getWriteCount());
         s.close();
     }
 
+    private void testRollback() {
+        MVStore s = MVStore.open(null);
+        MVMap<Integer, Integer> m = s.openMap("m");
+        m.put(1, -1);
+        s.commit();
+        for (int i = 0; i < 10; i++) {
+            m.put(1, i);
+            s.rollback();
+            assertEquals(i - 1, m.get(1).intValue());
+            m.put(1, i);
+            s.commit();
+        }
+    }
+
     private void testRollbackStored() {
         String fileName = getBaseDir() + "/testRollback.h3";
         FileUtils.delete(fileName);
@@ -1129,7 +1151,7 @@ public class TestMVStore extends TestBase {
         // so a new version is created
         m.put("1", "Hello");
 
-        long v2 = s.store();
+        long v2 = s.commit();
         assertEquals(2, v2);
         assertEquals(2, s.getCurrentVersion());
         assertFalse(s.hasUnsavedChanges());
@@ -1155,7 +1177,7 @@ public class TestMVStore extends TestBase {
         assertNull(meta.get("name.data1"));
         assertNull(m0.get("1"));
         assertEquals("Hello", m.get("1"));
-        assertEquals(2, s.store());
+        assertEquals(2, s.commit());
         s.close();
 
         s = openStore(fileName);
@@ -1179,7 +1201,6 @@ public class TestMVStore extends TestBase {
         assertEquals(3, s.getCurrentVersion());
         m = s.openMap("data");
         m.put("1",  "Hi");
-        s.store();
         s.close();
 
         s = openStore(fileName);
@@ -1243,7 +1264,7 @@ public class TestMVStore extends TestBase {
         MVMap<String, String> data = s.openMap("data");
         data.put("1", "Hello");
         data.put("2", "World");
-        s.store();
+        s.commit();
         assertEquals(1, s.getCurrentVersion());
         assertTrue(m.containsKey("chunk.1"));
         assertFalse(m.containsKey("chunk.2"));
@@ -1252,7 +1273,7 @@ public class TestMVStore extends TestBase {
         assertEquals("name:data", m.get("map." + id));
         assertTrue(m.containsKey("chunk.1"));
         assertEquals("Hello", data.put("1", "Hallo"));
-        s.store();
+        s.commit();
         assertEquals("name:data", m.get("map." + id));
         assertTrue(m.get("root.1").length() > 0);
         assertTrue(m.containsKey("chunk.1"));
@@ -1324,10 +1345,9 @@ public class TestMVStore extends TestBase {
                 m.put(i, o);
                 i++;
                 if (i % 10000 == 0) {
-                    s.store();
+                    s.commit();
                 }
             }
-            s.store();
             s.close();
             // System.out.println(prof.getTop(5));
             // System.out.println("store time " + (System.currentTimeMillis() - t));
@@ -1356,7 +1376,7 @@ public class TestMVStore extends TestBase {
         // p = new Profiler();
         //p.startCollecting();
         // t = System.currentTimeMillis();
-        s.store();
+        s.commit();
         // System.out.println("store: " + (System.currentTimeMillis() - t));
         // System.out.println(p.getTop(5));
         assertEquals("hello 0", m.remove(0));
@@ -1364,7 +1384,6 @@ public class TestMVStore extends TestBase {
         for (int i = 1; i < count; i++) {
             assertEquals("hello " + i, m.get(i));
         }
-        s.store();
         s.close();
 
         s = openStore(fileName);
@@ -1376,7 +1395,7 @@ public class TestMVStore extends TestBase {
         for (int i = 1; i < count; i++) {
             m.remove(i);
         }
-        s.store();
+        s.commit();
         assertNull(m.get(0));
         for (int i = 0; i < count; i++) {
             assertNull(m.get(i));
@@ -1394,7 +1413,7 @@ public class TestMVStore extends TestBase {
             for (int i = j * factor; i < 10 * factor; i++) {
                 m.put(i, "Hello" + j);
             }
-            s.store();
+            s.commit();
         }
         s.close();
 
@@ -1450,7 +1469,6 @@ public class TestMVStore extends TestBase {
             for (int i = 0; i < 100; i++) {
                 m.put(j + i, "Hello " + j);
             }
-            s.store();
             s.compact(80);
             s.close();
             long len = FileUtils.size(fileName);
@@ -1468,7 +1486,6 @@ public class TestMVStore extends TestBase {
         for (int i = 0; i < 100; i++) {
             m.remove(i);
         }
-        s.store();
         s.compact(80);
         s.close();
         // len = FileUtils.size(fileName);
@@ -1492,12 +1509,11 @@ public class TestMVStore extends TestBase {
             for (int i = 0; i < 10; i++) {
                 m.put(i, "Hello");
             }
-            s.store();
+            s.commit();
             for (int i = 0; i < 10; i++) {
                 assertEquals("Hello", m.get(i));
                 assertEquals("Hello", m.remove(i));
             }
-            s.store();
             s.close();
             long len = FileUtils.size(fileName);
             if (initialLength == 0) {
@@ -1584,7 +1600,6 @@ public class TestMVStore extends TestBase {
         si.put("Test", 10);
         MVMap<String, String> ss = s.openMap("stringString");
         ss.put("Hello", "World");
-        s.store();
         s.close();
         s = openStore(fileName);
         is = s.openMap("intString");
@@ -1608,7 +1623,7 @@ public class TestMVStore extends TestBase {
         for (int i = 0; i < 10; i++) {
             m.put(i, "hello " + i);
         }
-        s.store();
+        s.commit();
         it = m.keyIterator(null);
         it.next();
         assertThrows(UnsupportedOperationException.class, it).remove();
@@ -1639,7 +1654,6 @@ public class TestMVStore extends TestBase {
         for (int i = 0; i < 3; i++) {
             m.put(i, "hello " + i);
         }
-        s.store();
         // closing twice should be fine
         s.close();
         s.close();
@@ -1653,14 +1667,13 @@ public class TestMVStore extends TestBase {
         for (int i = 0; i < 3; i++) {
             m.put(i, "hello " + i);
         }
-        s.store();
+        s.commit();
         assertEquals("hello 0", m.remove(0));
 
         assertNull(m.get(0));
         for (int i = 1; i < 3; i++) {
             assertEquals("hello " + i, m.get(i));
         }
-        s.store();
         s.close();
 
         s = openStore(fileName);
@@ -1686,8 +1699,7 @@ public class TestMVStore extends TestBase {
         for (int i = 0;; i++) {
             map.put(i, data);
             if (i % 10000 == 0) {
-                long version = store.commit();
-                store.setRetainVersion(version);
+                store.commit();
                 long time = System.currentTimeMillis();
                 if (time - last > 2000) {
                     long mb = store.getFileStore().size() / 1024 / 1024;

h2/src/test/org/h2/test/store/TestRandomMapOps.java

@@ -92,7 +92,7 @@ public class TestRandomMapOps extends TestBase {
         for (; op < size; op++) {
             int k = r.nextInt(100);
             byte[] v = new byte[r.nextInt(10) * 10];
-            int type = r.nextInt(13);
+            int type = r.nextInt(12);
             switch (type) {
             case 0:
             case 1:
@@ -109,23 +109,19 @@ public class TestRandomMapOps extends TestBase {
                 map.remove(k);
                 break;
             case 6:
-                log(op, k, v, "s.store()");
-                s.store();
-                break;
-            case 7:
                 log(op, k, v, "s.compact(90)");
                 s.compact(90);
                 break;
-            case 8:
+            case 7:
                 log(op, k, v, "m.clear()");
                 m.clear();
                 map.clear();
                 break;
-            case 9:
+            case 8:
                 log(op, k, v, "s.commit()");
                 s.commit();
                 break;
-            case 10:
+            case 9:
                 log(op, k, v, "s.commit()");
                 s.commit();
                 log(op, k, v, "s.close()");
@@ -135,13 +131,13 @@ public class TestRandomMapOps extends TestBase {
                 log(op, k, v, "m = s.openMap(\"data\")");
                 m = s.openMap("data");
                 break;
-            case 11:
+            case 10:
                 log(op, k, v, "s.commit()");
                 s.commit();
                 log(op, k, v, "s.compactMoveChunks()");
                 s.compactMoveChunks();
                 break;
-            case 12:
+            case 11:
                 log(op, k, v, "m.getKeyIndex({0})");
                 ArrayList<Integer> keyList = new ArrayList<Integer>(map.keySet());
                 int index = Collections.binarySearch(keyList, k, null);
@@ -165,13 +161,12 @@ public class TestRandomMapOps extends TestBase {
                 assertEquals(map.lastKey(), m.lastKey());
             }
         }
-        s.store();
         s.close();
     }
 
     private static MVStore openStore(String fileName) {
         MVStore s = new MVStore.Builder().fileName(fileName).
-                pageSplitSize(50).writeDelay(0).open();
+                pageSplitSize(50).autoCommitDisabled().open();
         s.setRetentionTime(0);
         return s;
     }

h2/src/test/org/h2/test/store/TestStreamStore.java

@@ -65,7 +65,7 @@ public class TestStreamStore extends TestBase {
         for (int i = 0; i < 100; i++) {
             streamStore.put(new RandomStream(size, i));
         }
-        s.store();
+        s.commit();
         MVMap<Long, byte[]> map = s.openMap("data");
         assertTrue("size: " + map.size(), map.sizeAsLong() >= 100);
         s.close();
@@ -77,7 +77,7 @@ public class TestStreamStore extends TestBase {
         for (int i = 0; i < 100; i++) {
             streamStore.put(new RandomStream(size, -i));
         }
-        s.store();
+        s.commit();
         long readCount = s.getFileStore().getReadCount();
         // the read count should be low because new blocks
         // are appended at the end (not between existing blocks)
@@ -92,7 +92,7 @@ public class TestStreamStore extends TestBase {
         return new StreamStore(map) {
             @Override
             protected void onStore(int len) {
-                if (s.getUnsavedPageCount() > s.getUnsavedPageCountMax() / 2) {
+                if (s.getUnsavedPageCount() > s.getAutoCommitPageCount() / 2) {
                     s.commit();
                 }
             }
@@ -111,12 +111,11 @@ public class TestStreamStore extends TestBase {
             @Override
             protected void onStore(int len) {
                 count.incrementAndGet();
-                s.store();
+                s.commit();
             }
         };
         long size = 1 * 1024 * 1024;
         streamStore.put(new RandomStream(size, 0));
-        s.store();
         s.close();
         assertEquals(4, count.get());
     }

h2/src/test/org/h2/test/store/TestTransactionStore.java

@@ -86,7 +86,7 @@ public class TestTransactionStore extends TestBase {
                     for (int i = 0; !stop; i++) {
                         state.set(i);
                         other.put(i, value);
-                        store.store();
+                        store.commit();
                     }
                 }
             };