On a couple of micro benchmarks on a dev macbook using bleve-query on
an index of 50K wikipedia docs, scorch is now faster than
upsidedown/moss on high-freq term search "text:date"...
400 qps - upsidedown/moss
404 qps - scorch before
565 qps - scorch after
On a couple of micro benchmarks on a dev macbook using bleve-query on
an index of 50K wikipedia docs, scorch is now in more the same
neighborhood of upsidedown/moss...
high-freq term search "text:date"...
400 qps - upsidedown/moss
360 qps - scorch before
404 qps - scorch after
zero-freq term search "text:mschoch"...
100K qps - upsidedown/moss
55K qps - scorch before
99K qps - scorch after
Of note, the scorch index had ~150 *.zap files in it, which likely
made made the worker goroutine overhead more costly than for a case
with few segments, where goroutine and channel related work appeared
relatively prominently in the pprof SVG's.
The cachedDocs preparation has to happen for all docs in the field,
not just on the currently requested docNum.
Also, as part of this commit, there's a loop optimization where we no
longer use bytes.Split() on the terms buffer, thus avoiding garbage
creation.
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.
A new global variable, NumSnapshotsToKeep, represents the default
number of old snapshots that each scorch instance should maintain -- 0
is the default. Apps that need rollback'ability may want to increase
this value in early initialization.
The Scorch.eligibleForRemoval field tracks epoches which are safe to
delete from the rootBolt. The eligibleForRemoval is appended to
whenever the ref-count on an IndexSnapshot drops to 0.
On startup, eligibleForRemoval is also initialized with any older
epoch's found in the rootBolt.
The newly introduced Scorch.removeOldSnapshots() method is called on
every cycle of the persisterLoop(), where it maintains the
eligibleForRemoval slice to under a size defined by the
NumSnapshotsToKeep.
A future commit will remove actual storage files in order to match the
"source of truth" information found in the rootBolt.
