MVStore tests and bugfixes

h2/src/docsrc/html/mvstore.html

@@ -61,8 +61,8 @@ But it can be also directly within an application, without using JDBC or SQL.
 </li><li>Old versions of the data can be read concurrently with all other operations.
 </li><li>Transaction are supported (including concurrent transactions and 2-phase commit).
 </li><li>The tool is very modular. It supports pluggable data types / serialization,
-pluggable map implementations (B-tree, R-tree, concurrent B-tree currently), BLOB storage,
-and a file system abstraction to support encrypted files and zip files.
+    pluggable map implementations (B-tree, R-tree, concurrent B-tree currently), BLOB storage,
+    and a file system abstraction to support encrypted files and zip files.
 </li></ul>
 
 <h2 id="example_code">Example Code</h2>

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

@@ -38,11 +38,16 @@ public class MVMap<K, V> extends AbstractMap<K, V>
      * The current root page (may not be null).
      */
     protected volatile Page root;
-    
+
     /**
      * The version used for writing.
      */
-    protected long writeVersion;
+    protected volatile long writeVersion;
+
+    /**
+     * This version is set during a write operation.
+     */
+    protected volatile long currentWriteVersion = -1;
 
     private int id;
     private long createVersion;
@@ -53,11 +58,6 @@ public class MVMap<K, V> extends AbstractMap<K, V>
     private boolean closed;
     private boolean readOnly;
 
-    /**
-     * This flag is set during a write operation.
-     */
-    private volatile boolean writing;
-
     protected MVMap(DataType keyType, DataType valueType) {
         this.keyType = keyType;
         this.valueType = valueType;
@@ -934,14 +934,14 @@ public class MVMap<K, V> extends AbstractMap<K, V>
         }
         checkConcurrentWrite();
         store.beforeWrite();
-        writing = true;
+        currentWriteVersion = writeVersion;
     }
-
+    
     /**
      * Check that no write operation is in progress.
      */
     protected void checkConcurrentWrite() {
-        if (writing) {
+        if (currentWriteVersion != -1) {
             // try to detect concurrent modification
             // on a best-effort basis
             throw DataUtils.newConcurrentModificationException(getName());
@@ -953,17 +953,21 @@ public class MVMap<K, V> extends AbstractMap<K, V>
      * operation was successful).
      */
     protected void afterWrite() {
-        writing = false;
+        currentWriteVersion = -1;
     }
 
     /**
      * If there is a concurrent update to the given version, wait until it is
      * finished.
      *
-     * @param root the root page
+     * @param version the read version
      */
-    protected void waitUntilWritten(Page root) {
-        while (writing && root == this.root) {
+    protected void waitUntilWritten(long version) {
+        if (readOnly) {
+            throw DataUtils.newIllegalStateException(
+                    DataUtils.ERROR_INTERNAL, "Waiting for writes to a read-only map");
+        }
+        while (currentWriteVersion == version) {
             Thread.yield();
         }
     }
@@ -1136,6 +1140,10 @@ public class MVMap<K, V> extends AbstractMap<K, V>
     }
     
     void setWriteVersion(long writeVersion) {
+        if (readOnly) {
+            throw DataUtils.newIllegalStateException(
+                    DataUtils.ERROR_INTERNAL, "Trying to write to a read-only map");
+        }
         this.writeVersion = writeVersion;
     }
 

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

@@ -60,7 +60,7 @@ public class MVMapConcurrent<K, V> extends MVMap<K, V> {
     }
 
     @Override
-    protected void waitUntilWritten(Page root) {
+    protected void waitUntilWritten(long version) {
         // no need to wait
     }
 

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

@@ -49,17 +49,15 @@ TODO:
 TestMVStoreDataLoss
 
 TransactionStore:
-- write to the undo log _before_ a change (WAL style)
 
 MVStore:
 - rolling docs review: at "Features"
-- additional test async write / read algorithm for speed and errors
 - move setters to the builder, except for setRetainVersion, setReuseSpace,
     and settings that are persistent (setStoreVersion)
-- test meta rollback: it is changed after save; could rollback break it?
 - automated 'kill process' and 'power failure' test
 - update checkstyle
 - maybe split database into multiple files, to speed up compact
+    and allow using trim (by truncating / deleting empty files)
 - auto-compact from time to time and on close
 - test and possibly improve compact operation (for large dbs)
 - possibly split chunk metadata into immutable and mutable
@@ -68,17 +66,16 @@ MVStore:
 - chunk header: store changed chunk data as row; maybe after the root
 - chunk checksum (header, last page, 2 bytes per page?)
 - is there a better name for the file header,
--- if it's no longer always at the beginning of a file? store header?
+    if it's no longer always at the beginning of a file? store header?
 - on insert, if the child page is already full, don't load and modify it
--- split directly (specially for leaves with one large entry)
+    split directly (specially for leaves with one large entry)
 - maybe let a chunk point to a list of potential next chunks
--- (so no fixed location header is needed)
+    (so no fixed location header is needed), similar to a skip list
 - support stores that span multiple files (chunks stored in other files)
 - triggers (can be implemented with a custom map)
 - store number of write operations per page (maybe defragment
--- if much different than count)
+    if much different than count)
 - r-tree: nearest neighbor search
-- chunk metadata: do not store default values
 - support maps without values (just existence of the key)
 - support maps without keys (counted b-tree features)
 - use a small object cache (StringCache), test on Android
@@ -88,19 +85,19 @@ MVStore:
 - StreamStore optimization: avoid copying bytes
 - unlimited transaction size
 - MVStoreTool.shrink to shrink a store (create, copy, rename, delete)
+    and for MVStore on Windows, auto-detect renamed file
 - ensure data is overwritten eventually if the system doesn't have a timer
 - SSD-friendly write (always in blocks of 4 MB / 1 second?)
 - close the file on out of memory or disk write error (out of disk space or so)
 - implement a sharded map (in one store, multiple stores)
-- implement a sharded map (in one store, multiple stores)
+    to support concurrent updates and writes, and very large maps
 - implement an off-heap file system
 - remove change cursor, or add support for writing to branches
 - support pluggable logging or remove log
 - maybe add an optional finalizer and exit hook
     to store committed changes
 - to save space when persisting very small transactions,
-- to save space when persisting very small transactions,
+    use a transaction log where only the deltas are stored
 - serialization for lists, sets, sets, sorted sets, maps, sorted maps
 - maybe rename 'rollback' to 'revert' to distinguish from transactions
 - support other compression algorithms (deflate, LZ4,...)
@@ -110,6 +107,7 @@ MVStore:
 - autocommit (to avoid having to call commit, 
     as it could be called too often or it is easily forgotten)
 - remove features that are not really needed; simplify the code
+    possibly using a layering / tool mechanism
 - rename "store" to "save", as store collides with storeVersion
 
 */
@@ -914,15 +912,13 @@ public class MVStore {
         ArrayList<MVMap<?, ?>> list = New.arrayList(maps.values());
         ArrayList<MVMap<?, ?>> changed = New.arrayList();
         for (MVMap<?, ?> m : list) {
-            if (m != meta) {
-                m.setWriteVersion(version);
-                long v = m.getVersion();
-                if (v >= 0 && m.getVersion() >= lastStoredVersion) {
-                    MVMap<?, ?> r = m.openVersion(storeVersion);
-                    r.waitUntilWritten(r.getRoot());
-                    if (r.getRoot().getPos() == 0) {
-                        changed.add(r);
-                    }
+            m.setWriteVersion(version);
+            long v = m.getVersion();
+            if (v >= 0 && v >= lastStoredVersion) {
+                m.waitUntilWritten(storeVersion);
+                MVMap<?, ?> r = m.openVersion(storeVersion);
+                if (r.getRoot().getPos() == 0) {
+                    changed.add(r);
                 }
             }
         }
@@ -1359,10 +1355,12 @@ public class MVStore {
             unsavedPageCount = Math.max(0, unsavedPageCount - 1);
             return;
         }
-        // this could result in a cache miss
-        // if the operation is rolled back,
-        // but we don't optimize for rollback
+        
+        // This could result in a cache miss if the operation is rolled back,
+        // but we don't optimize for rollback.
+        // We could also keep the page in the cache, as somebody could read it.
         cache.remove(pos);
+        
         Chunk c = getChunk(pos);
         long version = currentVersion;
         if (map == meta && currentStoreVersion >= 0) {

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

@@ -43,9 +43,13 @@ public class TransactionStore {
     final MVMap<Long, Object[]> preparedTransactions;
 
     /**
-     * The undo log.
-     * If the first entry for a transaction doesn't have a logId of 0, then
-     * the transaction is committing (partially committed).
+     * The undo log. 
+     * <p>
+     * If the first entry for a transaction doesn't have a logId
+     * of 0, then the transaction is partially committed (which means rollback
+     * is not possible). Log entries are written before the data is changed
+     * (write-ahead). 
+     * <p>
      * Key: [ transactionId, logId ], value: [ opType, mapId, key, oldValue ].
      */
     final MVMap<long[], Object[]> undoLog;
@@ -228,6 +232,19 @@ public class TransactionStore {
         }
     }
 
+    /**
+     * Remove a log entry.
+     * 
+     * @param t the transaction
+     * @param logId the log id
+     */
+    public void logUndo(Transaction t, long logId) {
+        long[] undoKey = { t.getId(), logId };
+        synchronized (undoLog) {
+            undoLog.remove(undoKey);
+        }
+    }
+
     /**
      * Commit a transaction.
      *
@@ -581,6 +598,13 @@ public class TransactionStore {
         void log(int opType, int mapId, Object key, Object oldValue) {
             store.log(this, logId++, opType, mapId, key, oldValue);
         }
+        
+        /**
+         * Remove the last log entry.
+         */
+        void logUndo() {
+            store.logUndo(this, --logId);
+        }
 
         /**
          * Open a data map.
@@ -867,7 +891,7 @@ public class TransactionStore {
          * @param value the new value (null to remove the value)
          * @param onlyIfUnchanged only set the value if it was not changed (by
          *            this or another transaction) since the map was opened
-         * @return true if the value was set
+         * @return true if the value was set, false if there was a concurrent update
          */
         public boolean trySet(K key, V value, boolean onlyIfUnchanged) {
             VersionedValue current = map.get(key);
@@ -913,40 +937,38 @@ public class TransactionStore {
             newValue.value = value;
             if (current == null) {
                 // a new value
-                
-                int todo;
-                // either write the log before the data (and handle this case in rollback)
-                // or ensure/document concurrent commits are not allowed
-                
+                transaction.log(opType, mapId, key, current);
                 VersionedValue old = map.putIfAbsent(key, newValue);
-                if (old == null) {
-                    transaction.log(opType, mapId, key, current);
-                    return true;
+                if (old != null) {
+                    transaction.logUndo();
+                    return false;
                 }
-                return false;
+                return true;
             }
             long tx = current.transactionId;
             if (tx == transaction.transactionId) {
                 // added or updated by this transaction
-                if (map.replace(key, current, newValue)) {
-                    transaction.log(opType, mapId, key, current);
-                    return true;
+                transaction.log(opType, mapId, key, current);
+                if (!map.replace(key, current, newValue)) {
+                    // strange, somebody overwrite the value
+                    // even thought the change was not committed
+                    transaction.logUndo();
+                    return false;
                 }
-                // strange, somebody overwrite the value
-                // even thought the change was not committed
-                return false;
+                return true;
             }
             // added or updated by another transaction
             boolean open = transaction.store.isTransactionOpen(tx);
             if (!open) {
+                transaction.log(opType, mapId, key, current);
                 // the transaction is committed:
                 // overwrite the value
-                if (map.replace(key, current, newValue)) {
-                    transaction.log(opType, mapId, key, current);
-                    return true;
+                if (!map.replace(key, current, newValue)) {
+                    // somebody else was faster
+                    transaction.logUndo();
+                    return false;
                 }
-                // somebody else was faster
-                return false;
+                return true;
             }
             // the transaction is not yet committed
             return false;

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

@@ -45,7 +45,7 @@ public class TestTransactionStore extends TestBase {
     @Override
     public void test() throws Exception {
         FileUtils.createDirectories(getBaseDir());
-        // testStopWhileCommitting();
+        testStopWhileCommitting();
         testGetModifiedMaps();
         testKeyIterator();
         testMultiStatement();
@@ -60,12 +60,7 @@ public class TestTransactionStore extends TestBase {
         String fileName = getBaseDir() + "/testStopWhileCommitting.h3";
         FileUtils.delete(fileName);
 
-        for (int i = 0; i < 100;) {
-            System.out.println("i:" + i);
-//            this.printTime("i:" + i);
-
-//        for (int i = 0; i < 10;) {
-
+        for (int i = 0; i < 10;) {
             MVStore s;
             TransactionStore ts;
             Transaction tx;
@@ -87,7 +82,7 @@ public class TestTransactionStore extends TestBase {
 
                 @Override
                 public void call() throws Exception {
-                    for (int i = 0; state.get() < Integer.MAX_VALUE; i++) {
+                    for (int i = 0; !stop; i++) {
                         state.set(i);
                         other.put(i, value);
                         store.store();
@@ -101,8 +96,6 @@ public class TestTransactionStore extends TestBase {
             }
             // commit while writing in the task
             tx.commit();
-            // stop writing
-            state.set(Integer.MAX_VALUE);
             // wait for the task to stop
             task.get();
             store.close();