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don't check current key in DBIter::Next()

When iter_ is pointing to current key, we can safely move to the next
key to avoid checking current key, which is of course not necessary.

Benchmark shows that 'readseq' has about 8% performance improvement.

Without patch:

>./db_bench --benchmarks=readseq --num=$((4<<20)) --db=/tmp/db --use_existing_db=1
LevelDB:    version 1.21
Date:       Thu Apr 25 09:37:21 2019
CPU:        32 * Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz
CPUCache:   20480 KB
Keys:       16 bytes each
Values:     100 bytes each (50 bytes after compression)
Entries:    4194304
RawSize:    464.0 MB (estimated)
FileSize:   264.0 MB (estimated)
------------------------------------------------
readseq      :       0.196 micros/op;  565.7 MB/s

With patch:

>./db_bench --benchmarks=readseq --num=$((4<<20)) --db=/tmp/db --use_existing_db=1
LevelDB:    version 1.21
Date:       Thu Apr 25 09:38:20 2019
CPU:        32 * Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz
CPUCache:   20480 KB
Keys:       16 bytes each
Values:     100 bytes each (50 bytes after compression)
Entries:    4194304
RawSize:    464.0 MB (estimated)
FileSize:   264.0 MB (estimated)
------------------------------------------------
readseq      :       0.181 micros/op;  612.3 MB/s

Signed-off-by: Kyle Zhang <kyle@smartx.com>
naive_version
Kyle Zhang 5 년 전
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1개의 변경된 파일9개의 추가작업 그리고 0개의 파일을 삭제
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      db/db_iter.cc

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db/db_iter.cc 파일 보기

@ -168,6 +168,15 @@ void DBIter::Next() {
} else {
// Store in saved_key_ the current key so we skip it below.
SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
// iter_ is pointing to current key. We can now safely move to the next to
// avoid checking current key.
iter_->Next();
if (!iter_->Valid()) {
valid_ = false;
saved_key_.clear();
return;
}
}
FindNextUserEntry(true, &saved_key_);

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