Close translog writer if exception on write channel (#29401)

Today we close the translog write tragically if we experience any I/O
exception on a write. These tragic closes lead to use closing the
translog and failing the engine. Yet, there is one case that is missed
which is when we touch the write channel during a read (checking if
reading from the writer would put us past what has been flushed). This
commit addresses this by closing the writer tragically if we encounter
an I/O exception on the write channel while reading. This becomes
interesting when we consider that this method is invoked from the engine
through the translog as part of getting a document from the
translog. This means we have to consider closing the translog here as
well which will cascade up into us finally failing the engine.

Note that there is no semantic change to, for example, primary/replica
resync and recovery. These actions will take a snapshot of the translog
which syncs the translog to disk. If an I/O exception occurs during the
sync we already close the writer tragically and once we have synced we
do not ever read past the position that was synced while taking the
snapshot.
This commit is contained in:
Jason Tedor 2018-04-06 10:33:21 -04:00 committed by GitHub
parent 570f1d9ac7
commit cb3295b212
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2 changed files with 27 additions and 9 deletions

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@ -584,7 +584,16 @@ public class Translog extends AbstractIndexShardComponent implements IndexShardC
if (current.generation == location.generation) {
// no need to fsync here the read operation will ensure that buffers are written to disk
// if they are still in RAM and we are reading onto that position
try {
return current.read(location);
} catch (final IOException e) {
try {
closeOnTragicEvent(e);
} catch (final Exception inner) {
e.addSuppressed(inner);
}
throw e;
}
} else {
// read backwards - it's likely we need to read on that is recent
for (int i = readers.size() - 1; i >= 0; i--) {

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@ -380,6 +380,7 @@ public class TranslogWriter extends BaseTranslogReader implements Closeable {
@Override
protected void readBytes(ByteBuffer targetBuffer, long position) throws IOException {
try {
if (position + targetBuffer.remaining() > getWrittenOffset()) {
synchronized (this) {
// we only flush here if it's really really needed - try to minimize the impact of the read operation
@ -391,6 +392,14 @@ public class TranslogWriter extends BaseTranslogReader implements Closeable {
}
}
}
} catch (final IOException e) {
try {
closeWithTragicEvent(e);
} catch (final IOException inner) {
e.addSuppressed(inner);
}
throw e;
}
// we don't have to have a lock here because we only write ahead to the file, so all writes has been complete
// for the requested location.
Channels.readFromFileChannelWithEofException(channel, position, targetBuffer);