The optimizations / changes include...
- reuse of a memory buf when serializing varint's.
- reuse of a govarint.U64Base128Encoder instance, as it's a thin,
wrapper around an underlying chunkBuf, so Reset()'s on the
chunkBuf is enough for encoder reuse.
- chunkedIntcoder.Write() method was changed to invoke w.Write() less
often by forming a larger, reused buf. Profiling and analysis
showed w.Write() was getting called a lot, often with tiny 1 or 2
byte inputs. The theory is w.Write() and its underlying memmove()
can be more efficient when provided with larger bufs.
- some repeated code removal, by reusing the Close() method.
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.
The theory with this change is that the dicts and itrs should be
positionally in "lock-step" with paired entries.
And, since later code also uses the same array indexing to access the
drops and newDocNums, those also need to be positionally in pair-wise
lock-step, too.
Unlike vellum's MergeIterator, the enumerator introduced in this
commit doesn't merge when there are matching keys across iterators.
Instead, the enumerator implementation provides a traversal of all the
tuples of (key, iteratorIndex, val) from the underlying vellum
iterators, ordered by key ASC, iteratorIndex ASC.
During zap segment merging, a new zap PostingsIterator was allocated
for every field X segment X term.
This change optimizes by reusing a single PostingsIterator instance
per persistMergedRest() invocation.
And, also unused fields are removed from the PostingsIterator.
The optimization to byte-copy all the storedDocs for a given segment
during merging kicks in when the fields are the same across all
segments and when there are no deletions for that given segment. This
can happen, for example, during data loading or insert-only scenarios.
As part of this commit, the Segment.copyStoredDocs() method was added,
which uses a single Write() call to copy all the stored docs bytes of
a segment to a writer in one shot.
And, getDocStoredMetaAndCompressed() was refactored into a related
helper function, getDocStoredOffsets(), which provides the storedDocs
metadata (offsets & lengths) for a doc.
COMPATIBILITY NOTE: scorch zap version bumped in this commit.
The version bump is because mergeFields() now computes whether fields
are the same across segments and it relies on the previous commit
where fieldID's are assigned in field name sorted order (albeit with
_id field always having fieldID of 0).
Potential future commits might rely on this info that "fields are the
same across segments" for more optimizations, etc.
This is a stepping stone to allow easier future comparisons of field
maps and potential merge optimizations.
In bleve-blast tests on a 2015 macbook (50K wikipedia docs, 8
indexers, batch size 100, ssd), this does not seem to have a distinct
effect on indexing throughput.
This change turns zap.MergeToWriter() into a public func, so that it's
now directly callable from outside packages (such as from scorch's
top-level merger or persister). And, MergerToWriter() now takes input
of SegmentBases instead of Segments, so that it can now work on either
in-memory zap segments or file-based zap segments.
This is yet another stepping stone towards in-memory merging of zap
segments.
This change optimizes the scorch/mem DictionaryIterator by reusing a
DictEntry struct across multiple Next() calls. This follows the same
optimization trick and Next() semantics as upsidedown's FieldDict
implementation.
The zap DictionaryIterator Next() was incorrectly returning the
postingsList offset as the term count. As part of this, refactored
out a PostingsList.read() helper method.
Also added more merge unit test scenarios, including merging a segment
for a few rounds to see if there are differences before/after merging.
Instead of sorting docNum keys from a hashmap, this change instead
iterates from docNum 0 to N and uses an array instead of hashmap.
The array is also reused across outer loop iterations.
This optimizes for when there's a lot of structural similarity between
docs, where many/most docs have the same fields. i.e., beers,
breweries. If every doc has completely different fields, then this
change might produce worse behavior compared to the previous sparse
hashmap approach.
Instead of allocating a govarint.U64Base128Encoder in the inner loop,
allocate it just once on the outside, as it appears that it's just a
thin wrapper around binary.PutUvarint().
The zap SegmentBase struct is a refactoring of the zap Segment into
the subset of fields that are needed for read-only ops, without any
persistence related info. This allows us to use zap's optimized data
encoding as scorch's in-memory segments.
The zap Segment struct now embeds a zap SegmentBase struct, and layers
on persistence. Both the zap Segment and zap SegmentBase implement
scorch's Segment interface.
+ Account for all the overhead incurred from the data structures
within mem.Segment and zap.Segment.
- SizeOfMap = 8
- SizeOfPointer = 8
- SizeOfSlice = 24
- SizeOfString = 16
+ Include overhead from certain new fields as well.
This change preallocates more of the backing arrays for Locfields,
Locstarts, Locends, Locpos, Locaaraypos sub-slices of a scorch mem
segment.
On small bleve-blast tests (50K wiki docs) on a dev macbook, scorch
indexing throughput seems to improve from 15MB/sec to 20MB/sec after
the recent series of preallocation changes.
The scorch mem segment build phase uses the append() idiom to populate
various slices that are keyed by postings list id's. These slices
include...
* Postings
* PostingsLocs
* Freqs
* Norms
* Locfields
* Locstarts
* Locends
* Locpos
* Locarraypos
This change introduces an initialization step that preallocates those
slices up-front, by assigning postings list id's to terms up-front.
This change also has an additional effect of simplifying the
processDocument() logic to no longer have to worry about a first-time
initialization case, removing some duplicate'ish code.
