When the index is closed, do not fire an AsyncError (fatal) from either
the merger or the persister that is actively working. This is quite a
probable situation, so exit the loop within the goroutine.
As part of this, zap.MergeToWriter() now returns more information --
enough so that callers can now create their own SegmentBase instances.
Also, the fieldsMap maintained and returned by zap.MergeToWriter() is
now a mapping from fieldName ==> fieldID+1 (instead of the previous
mapping from fieldName ==> fieldID). This makes it similar to how
fieldsMap are handled in other parts of zap to avoid "zero value"
issues.
Two cases in this commit...
If we're shutting down, the merger might not have handed off its
latest merged segment to the introducer yet, so the merger still owns
the segment and needs to Close() that segment itself.
In persistSnapshot(), there migth be cases where the persister might
not be able to swap in its newly persisted segments -- so, the
persistSnapshot() needs to Close() those segments itself.
The slow merger was lagging behind the fast persister
to a persister notify send-loop while the persister awaits
for any new introductions from introducer totally blocking
the merger
This fix along with the deleted files eligibilty flipping
makes the file count to around 6 to 11 files per shard
for both travel and beer samples
A race & solution found by Marty Schoch... consider a case when the
merger might grab a nextSegmentID, like 4, but takes awhile to
complete. Meanwhile, the persister grabs the nextSegmentID of 5, but
finishes its persistence work fast, and then loops to cleanup any old
files. The simple approach of checking a "highest segment ID" of 5 is
wrong now, because the deleter now thinks that segment 4's zap file is
(incorrectly) ok to delete.
The solution in this commit is to track an ephemeral map of filenames
which are ineligibleForRemoval, because they're still being written
(by the merger) and haven't been fully incorporated into the rootBolt
yet.
The merger adds to that ineligibleForRemoval map as it starts a merged
zap file, the persister cleans up entries from that map when it
persists zap filenames into the rootBolt, and the deleter (part of the
persister's loop) consults the map before performing any actual zap
file deletions.
abhinavdangeti