sijie commented on a change in pull request #1281: Issue #570: Introducing 
EntryLogManager.
URL: https://github.com/apache/bookkeeper/pull/1281#discussion_r181599541
 
 

 ##########
 File path: 
bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/EntryLogger.java
 ##########
 @@ -788,89 +810,392 @@ private long readLastLogId(File f) {
         }
     }
 
-    /**
-     * Flushes all rotated log channels. After log channels are flushed,
-     * move leastUnflushedLogId ptr to current logId.
-     */
-    void checkpoint() throws IOException {
-        flushRotatedLogs();
+    interface EntryLogManager {
+
+        /*
+         * add entry to the corresponding entrylog and return the position of
+         * the entry in the entrylog
+         */
+        long addEntry(long ledger, ByteBuf entry, boolean rollLog) throws 
IOException;
+
+        /*
+         * gets the active logChannel with the given entryLogId. null if it is
+         * not existing.
+         */
+        BufferedLogChannel getCurrentLogIfPresent(long entryLogId);
+
+        /*
+         * Returns eligible writable ledger dir for the creation next entrylog
+         */
+        File getDirForNextEntryLog(List<File> writableLedgerDirs);
+
+        /*
+         * Do the operations required for checkpoint.
+         */
+        void checkpoint() throws IOException;
+
+        /*
+         * flush both current and rotated logs.
+         */
+        void flush() throws IOException;
+
+        /*
+         * close current logs.
+         */
+        void close() throws IOException;
+
+        /*
+         * force close current logs.
+         */
+        void forceClose();
+
         /*
-         * In the case of entryLogPerLedgerEnabled we need to flush both
-         * rotatedlogs and currentlogs. This is needed because syncThread
-         * periodically does checkpoint and at this time all the logs should
-         * be flushed.
          *
-         * TODO: When EntryLogManager is introduced in the subsequent 
sub-tasks of
-         * this Issue, I will move this logic to individual implamentations of
-         * EntryLogManager and it would be free of this booalen flag based 
logic.
+         */
+        void prepareSortedLedgerStorageCheckpoint(long numBytesFlushed) throws 
IOException;
+
+        /*
+         * this method should be called before doing entrymemtable flush, it
+         * would save the state of the entrylogger before entrymemtable flush
+         * and commitEntryMemTableFlush would take appropriate action after
+         * entrymemtable flush.
+         */
+        void prepareEntryMemTableFlush();
+
+        /*
+         * this method should be called after doing entrymemtable flush,it 
would
+         * take appropriate action after entrymemtable flush depending on the
+         * current state of the entrylogger and the state of the entrylogger
+         * during prepareEntryMemTableFlush.
+         *
+         * It is assumed that there would be corresponding
+         * prepareEntryMemTableFlush for every commitEntryMemTableFlush and 
both
+         * would be called from the same thread.
          *
+         * returns boolean value indicating whether EntryMemTable should do 
checkpoint
+         * after this commit method.
          */
-        if (entryLogPerLedgerEnabled) {
-            flushCurrentLog();
-        }
+        boolean commitEntryMemTableFlush() throws IOException;
     }
 
-    void flushRotatedLogs() throws IOException {
-        List<BufferedLogChannel> channels = null;
-        long flushedLogId = INVALID_LID;
-        synchronized (this) {
-            channels = logChannelsToFlush;
-            logChannelsToFlush = null;
+    abstract class EntryLogManagerBase implements EntryLogManager {
+        final List<BufferedLogChannel> rotatedLogChannels;
+
+        EntryLogManagerBase() {
+            rotatedLogChannels = new 
CopyOnWriteArrayList<BufferedLogChannel>();
         }
-        if (null == channels) {
-            return;
+
+        private final FastThreadLocal<ByteBuf> sizeBufferForAdd = new 
FastThreadLocal<ByteBuf>() {
+            @Override
+            protected ByteBuf initialValue() throws Exception {
+                return Unpooled.buffer(4);
+            }
+        };
+
+        /*
+         * This method should be guarded by a lock, so callers of this method
+         * should be in the right scope of the lock.
+         */
+        @Override
+        public long addEntry(long ledger, ByteBuf entry, boolean rollLog) 
throws IOException {
+            int entrySize = entry.readableBytes() + 4; // Adding 4 bytes to 
prepend the size
+            BufferedLogChannel logChannel = 
getCurrentLogForLedgerForAddEntry(ledger, entrySize, rollLog);
+            ByteBuf sizeBuffer = sizeBufferForAdd.get();
+            sizeBuffer.clear();
+            sizeBuffer.writeInt(entry.readableBytes());
+            logChannel.write(sizeBuffer);
+
+            long pos = logChannel.position();
+            logChannel.write(entry);
+            logChannel.registerWrittenEntry(ledger, entrySize);
+
+            return (logChannel.getLogId() << 32L) | pos;
         }
-        Iterator<BufferedLogChannel> chIter = channels.iterator();
-        while (chIter.hasNext()) {
-            BufferedLogChannel channel = chIter.next();
-            try {
-                channel.flushAndForceWrite(false);
-            } catch (IOException ioe) {
-                // rescue from flush exception, add unflushed channels back
-                synchronized (this) {
-                    if (null == logChannelsToFlush) {
-                        logChannelsToFlush = channels;
-                    } else {
-                        logChannelsToFlush.addAll(0, channels);
+
+        boolean reachEntryLogLimit(BufferedLogChannel logChannel, long size) {
+            if (logChannel == null) {
+                return false;
+            }
+            return logChannel.position() + size > logSizeLimit;
+        }
+
+        boolean readEntryLogHardLimit(BufferedLogChannel logChannel, long 
size) {
+            if (logChannel == null) {
+                return false;
+            }
+            return logChannel.position() + size > Integer.MAX_VALUE;
+        }
+
+        abstract BufferedLogChannel getCurrentLogForLedger(long ledgerId);
+
+        abstract BufferedLogChannel getCurrentLogForLedgerForAddEntry(long 
ledgerId, int entrySize, boolean rollLog)
+                throws IOException;
+
+        abstract void setCurrentLogForLedgerAndAddToRotate(long ledgerId, 
BufferedLogChannel logChannel);
+
+        /*
+         * flush current logs.
+         */
+        abstract void flushCurrentLogs() throws IOException;
+
+        List<BufferedLogChannel> getRotatedLogChannels() {
+            return rotatedLogChannels;
+        }
+
+        @Override
+        public void flush() throws IOException {
 
 Review comment:
   I am not convinced this change is correct. it seems to me this might only be 
needed when you changed from `volatile List<BufferedLogChannel>` to `final 
CopyOnWriteArrayList<BufferedLogChannel>`. 
   
   for sake of no changing the behavior of single-log manager, I would prefer 
keeping the behavior as same as before.

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