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HBASE-28184 Tailing the WAL is very slow if there are multiple peers #5505

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Nov 7, 2023
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HBASE-28184 Tailing the WAL is very slow if there are multiple peers #5505

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HBASE-28184 Tailing the WAL is very slow if there are multiple peers
shahrs87 Nov 6, 2023
7cfc57f
Merge branch 'branch-2.5' of https://github.com/apache/hbase into HBA…
shahrs87 Nov 6, 2023
78a74be
Addressing review comments
shahrs87 Nov 6, 2023
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21 changes: 20 additions & 1 deletion ...server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/WALEntryStream.java
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Original file line number Diff line number Diff line change
Expand Up @@ -258,7 +258,26 @@ private void dequeueCurrentLog() throws IOException {
private boolean readNextEntryAndRecordReaderPosition() throws IOException {
Entry readEntry = reader.next();
long readerPos = reader.getPosition();
OptionalLong fileLength = walFileLengthProvider.getLogFileSizeIfBeingWritten(currentPath);
OptionalLong fileLength;
if (logQueue.getQueueSize(walGroupId) > 1) {
// if there are more than one files in queue, although it is possible that we are
// still trying to write the trailer of the file and it is not closed yet, we can
// make sure that we will not write any WAL entries to it any more, so it is safe
// to just let the upper layer try to read the whole file without limit
fileLength = OptionalLong.empty();
} else {
// if there is only one file in queue, check whether it is still being written to
// we must call this before actually reading from the reader, as this method will acquire the
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For branch-2.5, the way we deal with empty queue problem is different. As there is no comment before this PR, let's just add 'if there is only one file in queue, check whether it is still being written to' comment here. The comments below are for branch-2+, where we have refactored the code a lot.

// rollWriteLock. This is very important, as we will enqueue the new WAL file in postLogRoll,
// and before this happens, we could have already finished closing the previous WAL file. If
// we do not acquire the rollWriteLock and return whether the current file is being written
// to, we may finish reading the previous WAL file and start to read the next one, before it
// is enqueued into the logQueue, thus lead to an empty logQueue and make the shipper think
// the queue is already ended and quit.I the future, if we want to optimize the logic here,
// for example, do not call this method every time, or do not acquire rollWriteLock in the
// implementation of this method, we need to carefully review the optimized implementation.
fileLength = walFileLengthProvider.getLogFileSizeIfBeingWritten(currentPath);
}
if (fileLength.isPresent() && readerPos > fileLength.getAsLong()) {
// See HBASE-14004, for AsyncFSWAL which uses fan-out, it is possible that we read uncommitted
// data, so we need to make sure that we do not read beyond the committed file length.
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