4 Commits (1db4a096d427892a0123d876618a38b7e162b001)

Author	SHA1	Message	Date
Abhishek Madan	457f77b9ff	Introduce RangeDelAggregatorV2 (#4649) ... Summary: The old RangeDelAggregator did expensive pre-processing work to create a collapsed, binary-searchable representation of range tombstones. With FragmentedRangeTombstoneIterator, much of this work is now unnecessary. RangeDelAggregatorV2 takes advantage of this by seeking in each iterator to find a covering tombstone in ShouldDelete, while doing minimal work in AddTombstones. The old RangeDelAggregator is still used during flush/compaction for now, though RangeDelAggregatorV2 will support those uses in a future PR. Pull Request resolved: https://github.com/facebook/rocksdb/pull/4649 Differential Revision: D13146964 Pulled By: abhimadan fbshipit-source-id: be29a4c020fc440500c137216fcc1cf529571eb3	6 years ago
Abhishek Madan	6bee36a786	Modify FragmentedRangeTombstoneList member layout (#4632) ... Summary: Rather than storing a `vector<RangeTombstone>`, we now store a `vector<RangeTombstoneStack>` and a `vector<SequenceNumber>`. A `RangeTombstoneStack` contains the start and end keys of a range tombstone fragment, and indices into the seqnum vector to indicate which sequence numbers the fragment is located at. The diagram below illustrates an example: ``` tombstones_: [a, b) [c, e) [h, k) | \ / \ / | | \ / \ / | v v v v tombstone_seqs_: [ 5 3 10 7 2 8 6 ] ``` This format allows binary searching the tombstone list to use less key comparisons, which helps in cases where there are many overlapping tombstones. Also, this format makes it easier to add DBIter-like semantics to `FragmentedRangeTombstoneIterator` in the future. Pull Request resolved: https://github.com/facebook/rocksdb/pull/4632 Differential Revision: D13053103 Pulled By: abhimadan fbshipit-source-id: e8220cc712fcf5be4d602913bb23ace8ea5f8ef0	6 years ago
Abhishek Madan	7528130e38	Cache fragmented range tombstones in BlockBasedTableReader (#4493) ... Summary: This allows tombstone fragmenting to only be performed when the table is opened, and cached for subsequent accesses. On the same DB used in #4449, running `readrandom` results in the following: ``` readrandom : 0.983 micros/op 1017076 ops/sec; 78.3 MB/s (63103 of 100000 found) ``` Now that Get performance in the presence of range tombstones is reasonable, I also compared the performance between a DB with range tombstones, "expanded" range tombstones (several point tombstones that cover the same keys the equivalent range tombstone would cover, a common workaround for DeleteRange), and no range tombstones. The created DBs had 5 million keys each, and DeleteRange was called at regular intervals (depending on the total number of range tombstones being written) after 4.5 million Puts. The table below summarizes the results of a `readwhilewriting` benchmark (in order to provide somewhat more realistic results): ``` Tombstones? | avg micros/op | stddev micros/op | avg ops/s | stddev ops/s ----------------- | ------------- | ---------------- | ------------ | ------------ None | 0.6186 | 0.04637 | 1,625,252.90 | 124,679.41 500 Expanded | 0.6019 | 0.03628 | 1,666,670.40 | 101,142.65 500 Unexpanded | 0.6435 | 0.03994 | 1,559,979.40 | 104,090.52 1k Expanded | 0.6034 | 0.04349 | 1,665,128.10 | 125,144.57 1k Unexpanded | 0.6261 | 0.03093 | 1,600,457.50 | 79,024.94 5k Expanded | 0.6163 | 0.05926 | 1,636,668.80 | 154,888.85 5k Unexpanded | 0.6402 | 0.04002 | 1,567,804.70 | 100,965.55 10k Expanded | 0.6036 | 0.05105 | 1,667,237.70 | 142,830.36 10k Unexpanded | 0.6128 | 0.02598 | 1,634,633.40 | 72,161.82 25k Expanded | 0.6198 | 0.04542 | 1,620,980.50 | 116,662.93 25k Unexpanded | 0.5478 | 0.0362 | 1,833,059.10 | 121,233.81 50k Expanded | 0.5104 | 0.04347 | 1,973,107.90 | 184,073.49 50k Unexpanded | 0.4528 | 0.03387 | 2,219,034.50 | 170,984.32 ``` After a large enough quantity of range tombstones are written, range tombstone Gets can become faster than reading from an equivalent DB with several point tombstones. Pull Request resolved: https://github.com/facebook/rocksdb/pull/4493 Differential Revision: D10842844 Pulled By: abhimadan fbshipit-source-id: a7d44534f8120e6aabb65779d26c6b9df954c509	6 years ago
Abhishek Madan	8c78348c77	Use only "local" range tombstones during Get (#4449) ... Summary: Previously, range tombstones were accumulated from every level, which was necessary if a range tombstone in a higher level covered a key in a lower level. However, RangeDelAggregator::AddTombstones's complexity is based on the number of tombstones that are currently stored in it, which is wasteful in the Get case, where we only need to know the highest sequence number of range tombstones that cover the key from higher levels, and compute the highest covering sequence number at the current level. This change introduces this optimization, and removes the use of RangeDelAggregator from the Get path. In the benchmark results, the following command was used to initialize the database: ``` ./db_bench -db=/dev/shm/5k-rts -use_existing_db=false -benchmarks=filluniquerandom -write_buffer_size=1048576 -compression_type=lz4 -target_file_size_base=1048576 -max_bytes_for_level_base=4194304 -value_size=112 -key_size=16 -block_size=4096 -level_compaction_dynamic_level_bytes=true -num=5000000 -max_background_jobs=12 -benchmark_write_rate_limit=20971520 -range_tombstone_width=100 -writes_per_range_tombstone=100 -max_num_range_tombstones=50000 -bloom_bits=8 ``` ...and the following command was used to measure read throughput: ``` ./db_bench -db=/dev/shm/5k-rts/ -use_existing_db=true -benchmarks=readrandom -disable_auto_compactions=true -num=5000000 -reads=100000 -threads=32 ``` The filluniquerandom command was only run once, and the resulting database was used to measure read performance before and after the PR. Both binaries were compiled with `DEBUG_LEVEL=0`. Readrandom results before PR: ``` readrandom : 4.544 micros/op 220090 ops/sec; 16.9 MB/s (63103 of 100000 found) ``` Readrandom results after PR: ``` readrandom : 11.147 micros/op 89707 ops/sec; 6.9 MB/s (63103 of 100000 found) ``` So it's actually slower right now, but this PR paves the way for future optimizations (see #4493). ---- Pull Request resolved: https://github.com/facebook/rocksdb/pull/4449 Differential Revision: D10370575 Pulled By: abhimadan fbshipit-source-id: 9a2e152be1ef36969055c0e9eb4beb0d96c11f4d	6 years ago