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5 Commits

Author SHA1 Message Date
Islam AbdelRahman
4a21b1402c Cache heap::downheap() root comparison (optimize heap cmp call) 
Summary:
Reduce number of comparisons in heap by caching which child node in the first level is smallest (left_child or right_child)
So next time we can compare directly against the smallest child

I see that the total number of calls to comparator drops significantly when using this optimization

Before caching (~2mil key comparison for iterating the DB)
```
$ DEBUG_LEVEL=0 make db_bench -j64 && ./db_bench --benchmarks="readseq" --db="/dev/shm/heap_opt" --use_existing_db --disable_auto_compactions --cache_size=1000000000  --perf_level=2
readseq      :       0.338 micros/op 2959201 ops/sec;  327.4 MB/s user_key_comparison_count = 2000008
```
After caching (~1mil key comparison for iterating the DB)
```
$ DEBUG_LEVEL=0 make db_bench -j64 && ./db_bench --benchmarks="readseq" --db="/dev/shm/heap_opt" --use_existing_db --disable_auto_compactions --cache_size=1000000000 --perf_level=2
readseq      :       0.309 micros/op 3236801 ops/sec;  358.1 MB/s user_key_comparison_count = 1000011
```

It also improves
Closes https://github.com/facebook/rocksdb/pull/1600

Differential Revision: D4256027

Pulled By: IslamAbdelRahman

fbshipit-source-id: 76fcc66
 2016-12-01 13:39:14 -08:00
Baraa Hamodi
21e95811d1 Updated all copyright headers to the new format. 2016-02-09 15:12:00 -08:00
lovro
e1c99e10c1 Replace std::priority_queue in MergingIterator with custom heap, take 2 
Summary: Repeat of b6655a679d (reverted in b7a2369fb2) with a proper fix for the issue that 57d216ea65 was trying to fix.

Test Plan:
make check

for i in $(seq 100); do ./db_stress --test_batches_snapshots=1 --threads=32 --write_buffer_size=4194304 --destroy_db_initially=0 --reopen=20 --readpercent=45 --prefixpercent=5 --writepercent=35 --delpercent=5 --iterpercent=10 --db=/tmp/rocksdb_crashtest_KdCI5F --max_key=100000000 --mmap_read=0 --block_size=16384 --cache_size=1048576 --open_files=500000 --verify_checksum=1 --sync=0 --progress_reports=0 --disable_wal=0 --disable_data_sync=1 --target_file_size_base=2097152 --target_file_size_multiplier=2 --max_write_buffer_number=3 --max_background_compactions=20 --max_bytes_for_level_base=10485760 --filter_deletes=0 --memtablerep=prefix_hash --prefix_size=7 --ops_per_thread=200 || break; done

Reviewers: anthony, sdong, igor, yhchiang

Reviewed By: igor, yhchiang

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D41391
 2015-07-15 03:34:40 -07:00
Yueh-Hsuan Chiang
b7a2369fb2 Revert "Replace std::priority_queue in MergingIterator with custom heap" 
Summary:
This patch reverts "Replace std::priority_queue in MergingIterator
with custom heap" (commit commit b6655a679d)
as it causes db_stress failure.

Test Plan: ./db_stress --test_batches_snapshots=1 --threads=32 --write_buffer_size=4194304 --destroy_db_initially=0 --reopen=20 --readpercent=45 --prefixpercent=5 --writepercent=35 --delpercent=5 --iterpercent=10 --db=/tmp/rocksdb_crashtest_KdCI5F --max_key=100000000 --mmap_read=0 --block_size=16384 --cache_size=1048576 --open_files=500000 --verify_checksum=1 --sync=0 --progress_reports=0 --disable_wal=0 --disable_data_sync=1 --target_file_size_base=2097152 --target_file_size_multiplier=2 --max_write_buffer_number=3 --max_background_compactions=20 --max_bytes_for_level_base=10485760 --filter_deletes=0 --memtablerep=prefix_hash --prefix_size=7 --ops_per_thread=200 --kill_random_test=97

Reviewers: igor, anthony, lovro, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D41343
 2015-07-07 14:45:20 -07:00
lovro
b6655a679d Replace std::priority_queue in MergingIterator with custom heap 
Summary:
While profiling compaction in our service I noticed a lot of CPU (~15% of compaction) being spent in MergingIterator and key comparison.  Looking at the code I found MergingIterator was (understandably) using std::priority_queue for the multiway merge.

Keys in our dataset include sequence numbers that increase with time.  Adjacent keys in an L0 file are very likely to be adjacent in the full database.  Consequently, compaction will often pick a chunk of rows from the same L0 file before switching to another one.  It would be great to avoid the O(log K) operation per row while compacting.

This diff replaces std::priority_queue with a custom binary heap implementation.  It has a "replace top" operation that is cheap when the new top is the same as the old one (i.e. the priority of the top entry is decreased but it still stays on top).

Test Plan:
make check

To test the effect on performance, I generated databases with data patterns that mimic what I describe in the summary (rows have a mostly increasing sequence number).  I see a 10-15% CPU decrease for compaction (and a matching throughput improvement on tmpfs).  The exact improvement depends on the number of L0 files and the amount of locality.  Performance on randomly distributed keys seems on par with the old code.

Reviewers: kailiu, sdong, igor

Reviewed By: igor

Subscribers: yoshinorim, dhruba, tnovak

Differential Revision: https://reviews.facebook.net/D29133
 2015-07-06 04:24:09 -07:00