MVStore - improvement to free space management - saves us from having to…

MVStore - improvement to free space management - saves us from having to generate a large BitSet every time we need to allocate a chunk

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

+package org.h2.mvstore;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class FreeSpaceList {
+
+    /** the first 2 pages are occupied by the file header. */
+    private static final int FIRST_FREE_PAGE = 2;
+    /** I use max_value/2 to avoid overflow errors during arithmetic. */
+    private static final int MAX_NO_PAGES = Integer.MAX_VALUE / 2;
+
+    private List<PageRange> freeSpaceList = new ArrayList<PageRange>();
+
+    public FreeSpaceList() {
+        freeSpaceList.add(new PageRange(FIRST_FREE_PAGE, MAX_NO_PAGES));
+    }
+
+    private static final class PageRange {
+        /** the start point, in pages */
+        public int start;
+        /** the length, in pages */
+        public int length;
+
+        public PageRange(int start, int length) {
+            this.start = start;
+            this.length = length;
+        }
+
+        @Override
+        public String toString() {
+            return "start:" + start + " length:" + length;
+        }
+    }
+
+    /**
+     * @return position in pages
+     */
+    public synchronized int allocatePages(long length) {
+        int required = (int) (length / MVStore.BLOCK_SIZE) + 1;
+        for (PageRange pr : freeSpaceList) {
+            if (pr.length >= required) {
+                return pr.start;
+            }
+        }
+        throw DataUtils.newIllegalStateException("could not find a free page to allocate");
+    }
+
+    public synchronized void markUsed(Chunk c) {
+        int chunkStart = (int) (c.start / MVStore.BLOCK_SIZE);
+        int required = (int) ((c.start + c.length) / MVStore.BLOCK_SIZE) + 2 - chunkStart;
+        PageRange found = null;
+        int i = 0;
+        for (PageRange pr : freeSpaceList) {
+            if (chunkStart >= pr.start && chunkStart < (pr.start + pr.length)) {
+                found = pr;
+                break;
+            }
+            i++;
+        }
+        if (found == null) {
+            throw DataUtils.newIllegalStateException("cannot find spot to mark chunk as used in free list, "
+                    + c.toString());
+        }
+        if (chunkStart + required > found.start + found.length) {
+            throw DataUtils.newIllegalStateException("chunk runs over edge of free space, " + c.toString());
+        }
+        if (found.start == chunkStart) {
+            // if the used-chunk is at the beginning of a free-space-range
+            found.start += required;
+            found.length -= required;
+            if (found.length == 0) {
+                // if the free-space-range is now empty, remove it
+                freeSpaceList.remove(i);
+            }
+        } else if (found.start + found.length == chunkStart + required) {
+            // if the used-chunk is at the end of a free-space-range
+            found.length -= required;
+            if (found.length == 0) {
+                // if the free-space-range is now empty, remove it
+                freeSpaceList.remove(i);
+            }
+        } else {
+            // it's in the middle, so split the existing entry
+            int length1 = chunkStart - found.start;
+            int start2 = chunkStart + required;
+            int length2 = found.start + found.length - chunkStart - required;
+
+            found.length = length1;
+            PageRange newRange = new PageRange(start2, length2);
+            freeSpaceList.add(i + 1, newRange);
+        }
+    }
+
+    public synchronized void markFree(Chunk c) {
+        int chunkStart = (int) (c.start / MVStore.BLOCK_SIZE);
+        int required = (c.length / MVStore.BLOCK_SIZE) + 1;
+        PageRange found = null;
+        int i = 0;
+        for (PageRange pr : freeSpaceList) {
+            if (pr.start > chunkStart) {
+                found = pr;
+                break;
+            }
+            i++;
+        }
+        if (found == null) {
+            throw DataUtils.newIllegalStateException("cannot find spot to mark chunk as unused in free list, "
+                    + c.toString());
+        }
+        if (chunkStart + required + 1 == found.start) {
+            // if the used-chunk is adjacent to the beginning of a
+            // free-space-range
+            found.start = chunkStart;
+            found.length += required;
+            // compactify-free-list: merge the previous entry into this one if
+            // they are now adjacent
+            if (i > 0) {
+                PageRange previous = freeSpaceList.get(i - 1);
+                if (previous.start + previous.length + 1 == found.start) {
+                    previous.length += found.length;
+                    freeSpaceList.remove(i);
+                }
+            }
+            return;
+        }
+        if (i > 0) {
+            // if the used-chunk is adjacent to the end of a free-space-range
+            PageRange previous = freeSpaceList.get(i - 1);
+            if (previous.start + previous.length + 1 == chunkStart) {
+                previous.length += required;
+                // compactify-free-list: merge the next entry into this one if
+                // they are now adjacent
+                if (previous.start + previous.length + 1 == found.start) {
+                    previous.length += found.length;
+                    freeSpaceList.remove(i);
+                }
+                return;
+            }
+        }
+
+        // it is between 2 entries, so add a new one
+        PageRange newRange = new PageRange(chunkStart, required);
+        freeSpaceList.add(i, newRange);
+    }
+
+    public synchronized void clear() {
+        freeSpaceList.clear();
+        freeSpaceList.add(new PageRange(FIRST_FREE_PAGE, MAX_NO_PAGES));
+    }
+
+    /** debug method */
+    public void dumpFreeList() {
+        StringBuilder buf = new StringBuilder("free list : ");
+        boolean first = true;
+        for (PageRange pr : freeSpaceList) {
+            if (first) {
+                first = false;
+            } else {
+                buf.append(", ");
+            }
+            buf.append(pr.start + "-" + (pr.start + pr.length - 1));
+        }
+        System.out.println(buf.toString());
+    }
+}

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

@@ -12,12 +12,12 @@ import java.nio.channels.FileChannel;
 import java.nio.channels.FileLock;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.BitSet;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import org.h2.compress.CompressLZF;
 import org.h2.compress.Compressor;
@@ -148,6 +148,11 @@ public class MVStore {
      */
     private final ConcurrentHashMap<Integer, Chunk> chunks =
             new ConcurrentHashMap<Integer, Chunk>();
+    /**
+     * The list of free spaces between the chunks.
+     */
+    private FreeSpaceList freeSpaceList = new FreeSpaceList();
+
 
     /**
      * The map of temporarily freed entries in the chunks. The key is the
@@ -564,6 +569,14 @@ public class MVStore {
             lastChunkId = Math.max(c.id, lastChunkId);
             chunks.put(c.id, c);
         }
+        // rebuild the free space list
+        freeSpaceList.clear();
+        for (Chunk c : chunks.values()) {
+            if (c.start == Long.MAX_VALUE) {
+                continue;
+            }
+            freeSpaceList.markUsed(c);
+        }
     }
 
     private void readFileHeader() {
@@ -694,6 +707,7 @@ public class MVStore {
                 }
                 meta = null;
                 chunks.clear();
+                freeSpaceList.clear();
                 cache.clear();
                 maps.clear();
             } catch (Exception e) {
@@ -848,7 +862,7 @@ public class MVStore {
         }
 
         applyFreedChunks(storeVersion);
-        ArrayList<Integer> removedChunks = New.arrayList();
+        Set<Integer> removedChunks = New.hashSet();
         // do it twice, because changing the meta table
         // could cause a chunk to become empty
         for (int i = 0; i < 2; i++) {
@@ -911,11 +925,13 @@ public class MVStore {
         // by an old version
         // so empty space is not reused too early
         for (int x : removedChunks) {
+            freeSpaceList.markFree(chunks.get(x));
             chunks.remove(x);
         }
 
         c.start = filePos;
         c.length = chunkLength;
+        freeSpaceList.markUsed(c);
         c.metaRootPos = meta.getRoot().getPos();
         buff.position(0);
         c.writeHeader(buff);
@@ -1036,33 +1052,7 @@ public class MVStore {
     }
 
     private long allocateChunk(long length) {
-        BitSet set = new BitSet();
-        set.set(0);
-        set.set(1);
-        for (Chunk c : chunks.values()) {
-            if (c.start == Long.MAX_VALUE) {
-                continue;
-            }
-            int first = (int) (c.start / BLOCK_SIZE);
-            int last = (int) ((c.start + c.length) / BLOCK_SIZE);
-            set.set(first, last + 2);
-        }
-        int required = (int) (length / BLOCK_SIZE) + 1;
-        for (int i = 0; i < set.size(); i++) {
-            if (!set.get(i)) {
-                boolean ok = true;
-                for (int j = 0; j < required; j++) {
-                    if (set.get(i + j)) {
-                        ok = false;
-                        break;
-                    }
-                }
-                if (ok) {
-                    return i * BLOCK_SIZE;
-                }
-            }
-        }
-        return set.size() * BLOCK_SIZE;
+        return ((long) freeSpaceList.allocatePages(length)) * BLOCK_SIZE;
     }
 
     /**
@@ -1500,6 +1490,7 @@ public class MVStore {
             }
             meta.clear();
             chunks.clear();
+            freeSpaceList.clear();
             maps.clear();
             synchronized (freedChunks) {
                 freedChunks.clear();
@@ -1530,6 +1521,7 @@ public class MVStore {
                 loadFromFile = true;
                 do {
                     last = chunks.remove(lastChunkId);
+                    freeSpaceList.markFree(last);
                     lastChunkId--;
                 } while (last.version > version && chunks.size() > 0);
                 rootChunkStart = last.start;

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

@@ -79,6 +79,10 @@ public class TestMVStore extends TestBase {
         testIterate();
         testCloseTwice();
         testSimple();
+        // this test will run out of memory on a 32-bit VM before it gets to the part we need it to test
+        if ("64".equals(System.getProperty("sun.arch.data.model"))) { 
+            testLargerThan2G();
+        }
     }
 
     private void testAtomicOperations() {
@@ -1393,6 +1397,32 @@ public class TestMVStore extends TestBase {
         s.close();
     }
     
+    private void testLargerThan2G() {
+        String fileName = getBaseDir() + "/testLargerThan2G.h3";
+        FileUtils.delete(fileName);
+        
+        MVStore store = new MVStore.Builder().cacheSize(800).fileName(fileName).writeBufferSize(0).writeDelay(-1)
+                .open();
+
+        MVMap<String, String> map = store.openMap("test");
+        int totalWrite = 15000000;
+        int lineStored = 0;
+        while (lineStored <= totalWrite) {
+            lineStored++;
+            String actualKey = lineStored + " just for length length length    " + lineStored;
+            String value = "Just a a string that is kinda long long long but not too much much much much much much much much much   "
+                    + lineStored;
+
+            map.put(actualKey, value);
+
+            if (lineStored % 1000000 == 0) {
+                store.store();
+            }
+        }
+        store.store();
+        store.close();
+    }
+
     /**
      * Open a store for the given file name, using a small page size.
      *