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Only requeue compaction when there was activity #759

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Nov 9, 2018
Merged

Only requeue compaction when there was activity #759

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16 changes: 11 additions & 5 deletions server/tserver/src/main/java/org/apache/accumulo/tserver/tablet/CompactionRunner.java
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Original file line number Diff line number Diff line change
Expand Up @@ -41,12 +41,18 @@ public void run() {
return;
}

tablet.majorCompact(reason, queued);
CompactionStats stats = tablet.majorCompact(reason, queued);
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I would have thought Spotbugs would have dinged this method returning stats that aren't being used...


// if there is more work to be done, queue another major compaction
synchronized (tablet) {
if (reason == MajorCompactionReason.NORMAL && tablet.needsMajorCompaction(reason))
tablet.initiateMajorCompaction(reason);
// Some compaction strategies may always return true for shouldCompact() because they need to
// make blocking calls to gather information. Without the following check these strategies would
// endlessly requeue. So only check if a subsequent compaction is needed if the previous
// compaction actually did something.
if (stats != null && stats.getEntriesRead() > 0) {
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Won't this prevent compactions from happening when stats.getEntriesRead() == 0?

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No, tablets are checked periodically to see if they need a compaction by the tablet server. This code is just an optimization to re-queue the tablet for compaction if there is still work to do (without waiting for the periodic check). If we run a compaction and it does nothing, its likely there is no follow on compaction work to be done.

For background, tablets are limited in the number of files they will compact at once. So if a tablet had 100 files to compact and the limit is 20, then when it compacts 20 files it would be nice if immediately re-queued instead of waiting for the tablet server to check all tablets again. With these changes, it will still re-queued immediately in that case.

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OK thanks for making that clear.

// if there is more work to be done, queue another major compaction
synchronized (tablet) {
if (reason == MajorCompactionReason.NORMAL && tablet.needsMajorCompaction(reason))
tablet.initiateMajorCompaction(reason);
}
}
}

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