Commit Graph

112 Commits

Author SHA1 Message Date
mrambacher 12f1137355 Add a SystemClock class to capture the time functions of an Env (#7858)
Summary:
Introduces and uses a SystemClock class to RocksDB.  This class contains the time-related functions of an Env and these functions can be redirected from the Env to the SystemClock.

Many of the places that used an Env (Timer, PerfStepTimer, RepeatableThread, RateLimiter, WriteController) for time-related functions have been changed to use SystemClock instead.  There are likely more places that can be changed, but this is a start to show what can/should be done.  Over time it would be nice to migrate most (if not all) of the uses of the time functions from the Env to the SystemClock.

There are several Env classes that implement these functions.  Most of these have not been converted yet to SystemClock implementations; that will come in a subsequent PR.  It would be good to unify many of the Mock Timer implementations, so that they behave similarly and be tested similarly (some override Sleep, some use a MockSleep, etc).

Additionally, this change will allow new methods to be introduced to the SystemClock (like https://github.com/facebook/rocksdb/issues/7101 WaitFor) in a consistent manner across a smaller number of classes.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7858

Reviewed By: pdillinger

Differential Revision: D26006406

Pulled By: mrambacher

fbshipit-source-id: ed10a8abbdab7ff2e23d69d85bd25b3e7e899e90
2021-01-25 22:09:11 -08:00
Akanksha Mahajan 30a5ed9c53 Update "num_data_read" stat in RetrieveMultipleBlocks (#7770)
Summary:
RetrieveMultipleBlocks which is used by MultiGet to read data blocks is not updating num_data_read stat in
GetContextStats.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7770

Test Plan: make check -j64

Reviewed By: anand1976

Differential Revision: D25538982

Pulled By: akankshamahajan15

fbshipit-source-id: e3daedb035b1be8ab6af6f115cb3793ccc7b1ec6
2020-12-23 15:16:46 -08:00
anand76 8a1488efbf Ensure that MultiGet works properly with compressed cache (#7756)
Summary:
Ensure that when direct IO is enabled and a compressed block cache is
configured, MultiGet inserts compressed data blocks into the compressed
block cache.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7756

Test Plan: Add unit test to db_basic_test

Reviewed By: cheng-chang

Differential Revision: D25416240

Pulled By: anand1976

fbshipit-source-id: 75d57526370c9c0a45ff72651f3278dbd8a9086f
2020-12-09 17:01:13 -08:00
Jay Zhuang 9e1640403a Exclude timestamp from prefix extractor (#7668)
Summary:
Timestamp should not be included in prefix extractor, as we discussed here: https://github.com/facebook/rocksdb/pull/7589#discussion_r511068586

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7668

Test Plan: added unittest

Reviewed By: riversand963

Differential Revision: D24966265

Pulled By: jay-zhuang

fbshipit-source-id: 0dae618c333d4b7942a40d556535a1795e060aea
2020-12-01 14:07:15 -08:00
Jay Zhuang 881e0dcc09 Fix MultiGet unable to query timestamp data issue (#7589)
Summary:
The filter query key should not contain timestamp. The timestamp is
stripped for Get(), but not MultiGet().

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7589

Reviewed By: riversand963

Differential Revision: D24494661

Pulled By: jay-zhuang

fbshipit-source-id: fc5ff40f9d683a89a760c6ff0ab3aed05a70c317
2020-11-03 09:45:41 -08:00
Yanqin Jin 394210f280 Remove unused includes (#7604)
Summary:
This is a PR generated **semi-automatically** by an internal tool to remove unused includes and `using` statements.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7604

Test Plan: make check

Reviewed By: ajkr

Differential Revision: D24579392

Pulled By: riversand963

fbshipit-source-id: c4bfa6c6b08da1de186690d37eb73d8fff45aecd
2020-10-28 23:22:27 -07:00
Ramkumar Vadivelu 9a690a74e1 In ParseInternalKey(), include corrupt key info in Status (#7515)
Summary:
Fixes Issue https://github.com/facebook/rocksdb/issues/7497

When allow_data_in_errors db_options is set, log error key details in `ParseInternalKey()`

Have fixed most of the calls. Have few TODOs still pending - because have to make more deeper changes to pass in the allow_data_in_errors flag. Will do those in a separate PR later.

Tests:
- make check
- some of the existing tests that exercise the "internal key too small" condition are: dbformat_test, cuckoo_table_builder_test
- some of the existing tests that exercise the corrupted key path are: corruption_test, merge_helper_test, compaction_iterator_test

Example of new status returns:
- Key too small - `Corrupted Key: Internal Key too small. Size=5`
- Corrupt key with allow_data_in_errors option set to false: `Corrupted Key: '<redacted>' seq:3, type:3`
- Corrupt key with allow_data_in_errors option set to true: `Corrupted Key: '61' seq:3, type:3`

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7515

Reviewed By: ajkr

Differential Revision: D24240264

Pulled By: ramvadiv

fbshipit-source-id: bc48f5d4475ac19d7713e16df37505b31aac42e7
2020-10-28 10:12:58 -07:00
Akanksha Mahajan b4cd51d847 Fix for stress test failure (#7574)
Summary:
Ignore read error in 'FilePrefetchBuffer::TryReadFromCache' as status is ignored
and  bool value is returned. Return error if prefetch fails in
'PrefetchTail' as we have planned to return Prefetch failures to users.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7574

Test Plan:
make check -j64,
python -u tools/db_crashtest.py blackbox

Reviewed By: zhichao-cao

Differential Revision: D24408825

Pulled By: akankshamahajan15

fbshipit-source-id: feebda771415998253fbe54632f13e6e75b7a243
2020-10-20 09:13:42 -07:00
Akanksha Mahajan db87afbcb3 Return error if Get/Multi() fails in Prefetching Filter blocks (#7543)
Summary:
Right now all I/O failures under
PartitionFilterBlock::CacheDependencies() is swallowed. Return error in
case prefetch fails.

On returning error in PartitionedFilterBlockReader::CacheDependencies was causing stress test failure because PrefetchBuffer is initialized with enable_ = true, as result when PosixMmapReadableFile::Read is called from Prefetch, scratch is ignored causing buffer to fill with garbage values. Initializing prefetch buffer by CreatePrefetchBuffer that sets enable_ with !ioptions.allow_mmap_reads fixed the problem as it returns without prefetching data if allow_mmap_reads is set.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7543

Test Plan:
make check -j64;
python -u tools/db_crashtest.py --simple blackbox

Reviewed By: anand1976

Differential Revision: D24284596

Pulled By: akankshamahajan15

fbshipit-source-id: f3f0fd44b59dcf60645730436f28564a07884868
2020-10-14 10:45:36 -07:00
Andrew Kryczka 75d3b6fdf0 Redesign block cache pinning API (#7520)
Summary:
The old flag-based APIs (`BlockBasedTableOptions::pin_l0_filter_and_index_blocks_in_cache` and `BlockBasedTableOptions::pin_top_level_index_and_filter`) were insufficient for our needs. For example, it was impossible to pin only unpartitioned meta-blocks, which could prevent block cache contention when turning on dictionary compression or during a migration to partitioned indexes/filters. It was also impossible to pin all meta-blocks in memory while having predictable memory usage via block cache. If we had continued adding flags to address these scenarios, they would have had significant overlap causing confusion. Instead, this PR deprecates the flags and starts a new API with non-overlapping options.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7520

Test Plan:
- new unit test
- added new options to stress/crash test and ran for a while: `$ python tools/db_crashtest.py blackbox --simple --max_key=1000000 -write_buffer_size=1048576 -target_file_size_base=1048576 -max_bytes_for_level_base=4194304 --interval=10 -value_size_mult=33 -column_families=1 -reopen=0`

Reviewed By: pdillinger

Differential Revision: D24200034

Pulled By: ajkr

fbshipit-source-id: 3fa7cfc71e7960f7a867511dd6ae5834dd73b13e
2020-10-11 14:58:24 -07:00
Akanksha Mahajan 24498ab1ec Add few unit test cases in ASSERT_STATUS_CHECKED (#7500)
Summary:
Add status enforcement for following tests:
  1. import_column_family_test
  2. memory_test
  3. table_test

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7500

Reviewed By: zhichao-cao

Differential Revision: D24095887

Pulled By: akankshamahajan15

fbshipit-source-id: db8e1ec595852df143fad78a0c07bfdd27dc3c84
2020-10-08 11:22:44 -07:00
Akanksha Mahajan 38d0a365e3 Add Stats for MultiGet (#7366)
Summary:
Add following stats for MultiGet in Histogram to get more insight on MultiGet.
    1. Number of index and filter blocks read from file as part of MultiGet
    request per level.
    2. Number of data blocks read from file per level.
    3. Number of SST files loaded from file system per level.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7366

Reviewed By: anand1976

Differential Revision: D24127040

Pulled By: akankshamahajan15

fbshipit-source-id: e63a003056b833729b277edc0639c08fb432756b
2020-10-07 13:28:48 -07:00
Levi Tamasi 5d16325ce3 Revert "Return error if Get() fails in Prefetching Filter blocks (#7463)" (#7505)
Summary:
This reverts commit 7d503e66a9.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7505

Reviewed By: ajkr

Differential Revision: D24100875

Pulled By: ltamasi

fbshipit-source-id: 8705e3e6e8be4b4fd175ffdb031baa6530b61151
2020-10-03 18:38:04 -07:00
Akanksha Mahajan 7d503e66a9 Return error if Get() fails in Prefetching Filter blocks (#7463)
Summary:
Right now all I/O failures under
PartitionFilterBlock::CacheDependencies() is swallowed. Return error in
case prefetch fails.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7463

Test Plan: make check -j64

Reviewed By: anand1976

Differential Revision: D24008226

Pulled By: akankshamahajan15

fbshipit-source-id: b65d63b2d01465db92500b78de7ad58650ec9b3b
2020-10-02 19:40:43 -07:00
Ramkumar Vadivelu e04a50923d Change ParseInternalKey() to return Status instead of bool (#7457)
Summary:
Fixes https://github.com/facebook/rocksdb/issues/7430

Change ParseInternalKey() to return Status instead of bool.

db_bench (seekrandom) based before/after results with value size of 100 bytes and 16 bytes can be found at (tests ran on an udb server):
https://www.dropbox.com/s/47bwamdy5ozngph/PIK_ret_Status_results.xlsx?dl=0

![db_bench_results](https://user-images.githubusercontent.com/62277872/94642825-2a21a800-029a-11eb-88f2-124136c83fd3.png)

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7457

Reviewed By: ajkr

Differential Revision: D24002433

Pulled By: ramvadiv

fbshipit-source-id: ac253ecf577a29044c47c3fe254a01e71404c44c
2020-09-30 19:16:47 -07:00
Jay Zhuang 1bdaef7a06 Status check enforcement for timestamp_basic_test (#7454)
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/7454

Reviewed By: riversand963

Differential Revision: D23981719

Pulled By: jay-zhuang

fbshipit-source-id: 01073f73e54c17067b886c4a2f179b2804198399
2020-09-29 18:23:27 -07:00
sdong d08a9005b7 Make db_basic_test pass assert status checked (#7452)
Summary:
Add db_basic_test status check list. Some of the warnings are suppressed. It is possible that some of them are due to real bugs.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7452

Test Plan: See CI tests pass.

Reviewed By: zhichao-cao

Differential Revision: D23979764

fbshipit-source-id: 6151570c2a9b931b0fbb3fe939a94b2bd1583cbe
2020-09-29 09:49:04 -07:00
Jay Zhuang 8a8a01c642 Fix compile error for old gcc-4.8 (#7358)
Summary:
gcc-4.8 returns error when using the constructor. Not sure if it's a compiler bug/limitation or code issue:
```
table/block_based/block_based_table_reader.cc:3183:67: error: use of deleted function ‘rocksdb::WritableFileStringStreamAdapter::WritableFileStringStreamAdapter(rocksdb::WritableFileStringStreamAdapter&&)’
```

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7358

Reviewed By: pdillinger

Differential Revision: D23577651

Pulled By: jay-zhuang

fbshipit-source-id: b0197e3d3538da61a6f3866410d88d2047fb9695
2020-09-08 12:09:34 -07:00
Jay Zhuang 27aa443a15 Add sst_file_dumper status check (#7315)
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/7315

Test Plan:
`ASSERT_STATUS_CHECKED=1 make sst_dump_test && ./sst_dump_test`
And manually run `./sst_dump --file=*.sst` before and after the change.

Reviewed By: pdillinger

Differential Revision: D23361669

Pulled By: jay-zhuang

fbshipit-source-id: 5bf51a2a90ee35c8c679e5f604732ec2aef5949a
2020-09-04 19:26:42 -07:00
Jay Zhuang c2485f2d81 Add buffer prefetch support for non directIO usecase (#7312)
Summary:
A new file interface `SupportPrefetch()` is added. When the user overrides it to `false`, an internal prefetch buffer will be used for readahead. Useful for non-directIO but FS doesn't have readahead support.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7312

Reviewed By: anand1976

Differential Revision: D23329847

Pulled By: jay-zhuang

fbshipit-source-id: 71cd4ce6f4a820840294e4e6aec111ab76175527
2020-08-27 18:16:53 -07:00
sdong 722814e357 Get() to fail with underlying failures in PartitionIndexReader::CacheDependencies() (#7297)
Summary:
Right now all I/O failures under PartitionIndexReader::CacheDependencies() is swallowed. This doesn't impact correctness but we've made a decision that any I/O error in read path now should be returned to users for awareness. Return errors in those cases instead.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7297

Test Plan: Add a new unit test that ingest errors in this code path and see Get() fails. Only one I/O path is hit in PartitionIndexReader::CacheDependencies(). Several option changes are attempt but not able to got other pread paths triggered. Not sure whether other failure cases would be even possible. Would rely on continuous stress test to validate it.

Reviewed By: anand1976

Differential Revision: D23257950

fbshipit-source-id: 859dbc92fa239996e1bb378329344d3d54168c03
2020-08-25 19:01:05 -07:00
anand76 832b056a30 Enable IO timeouts for iterators (#7161)
Summary:
Introduce io_timeout in ReadOptions and enabled deadline/io_timeout for
Iterators.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7161

Test Plan: New unit tests in db_basic_test

Reviewed By: riversand963

Differential Revision: D22687352

Pulled By: anand1976

fbshipit-source-id: 67bbb0e6d7ae80b256589244468494292538c6ec
2020-08-07 12:01:08 -07:00
Andrew Kryczka dd29ad4223 Separate internal and user key comparators in `BlockIter` (#6944)
Summary:
Replace `BlockIter::comparator_` and `IndexBlockIter::user_comparator_wrapper_` with a concrete `UserComparatorWrapper` and `InternalKeyComparator`. The motivation for this change was the inconvenience of not knowing the concrete type of `BlockIter::comparator_`, which prevented calling specialized internal key comparison functions to optimize comparison of keys with global seqno applied.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/6944

Test Plan:
benchmark setup -- single file DBs, in-memory, no compression. "normal_db"
created by regular flush; "ingestion_db" created by ingesting a file. Both
DBs have same contents.

```
$ TEST_TMPDIR=/dev/shm/normal_db/ ./db_bench -benchmarks=fillrandom,compact -write_buffer_size=10485760000 -disable_auto_compactions=true -compression_type=none -num=1000000
$ ./ldb write_extern_sst ./tmp.sst --db=/dev/shm/ingestion_db/dbbench/ --compression_type=no --hex --create_if_missing < <(./sst_dump --command=scan --output_hex --file=/dev/shm/normal_db/dbbench/000007.sst | awk 'began {print "0x" substr($1, 2, length($1) - 2), "==>", "0x" $5} ; /^Sst file format: block-based/ {began=1}')
$ ./ldb ingest_extern_sst ./tmp.sst --db=/dev/shm/ingestion_db/dbbench/
```

benchmark run command:

```
$ TEST_TMPDIR=/dev/shm/$DB/ ./db_bench -benchmarks=seekrandom -seek_nexts=$SEEK_NEXT -use_existing_db=true -cache_index_and_filter_blocks=false -num=1000000 -cache_size=0 -threads=1 -reads=200000000 -mmap_read=1 -verify_checksum=false
```

results: perf improved marginally for ingestion_db and did not change significantly for normal_db:

SEEK_NEXT | DB | code | ops/sec | % change
-- | -- | -- | -- | --
0 | normal_db | master | 350880 |  
0 | normal_db | PR6944 | 351040 | 0.0
0 | ingestion_db | master | 343255 |  
0 | ingestion_db | PR6944 | 349424 | 1.8
10 | normal_db | master | 218711 |  
10 | normal_db | PR6944 | 217892 | -0.4
10 | ingestion_db | master | 220334 |  
10 | ingestion_db | PR6944 | 226437 | 2.8

Reviewed By: pdillinger

Differential Revision: D21924676

Pulled By: ajkr

fbshipit-source-id: ea4288a2eefa8112eb6c651a671c1de18c12e538
2020-07-07 17:26:16 -07:00
Anand Ananthabhotla 9a5886bd8c Extend Get/MultiGet deadline support to table open (#6982)
Summary:
Current implementation of the ```read_options.deadline``` option only checks the deadline for random file reads during point lookups. This PR extends the checks to file opens, prefetches and preloads as part of table open.

The main changes are in the ```BlockBasedTable```, partitioned index and filter readers, and ```TableCache``` to take ReadOptions as an additional parameter. In ```BlockBasedTable::Open```, in order to retain existing behavior w.r.t checksum verification and block cache usage, we filter out most of the options in ```ReadOptions``` except ```deadline```. However, having the ```ReadOptions``` gives us more flexibility to honor other options like verify_checksums, fill_cache etc. in the future.

Additional changes in callsites due to function signature changes in ```NewTableReader()``` and ```FilePrefetchBuffer```.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6982

Test Plan: Add new unit tests in db_basic_test

Reviewed By: riversand963

Differential Revision: D22219515

Pulled By: anand1976

fbshipit-source-id: 8a3b92f4a889808013838603aa3ca35229cd501b
2020-06-29 14:53:17 -07:00
Peter Dillinger 25a0d0ca30 Fix block checksum for >=4GB, refactor (#6978)
Summary:
Although RocksDB falls over in various other ways with KVs
around 4GB or more, this change fixes how XXH32 and XXH64 were being
called by the block checksum code to support >= 4GB in case that should
ever happen, or the code copied for other uses.

This change is not a schema compatibility issue because the checksum
verification code would checksum the first (block_size + 1) mod 2^32
bytes while the checksum construction code would checksum the first
block_size mod 2^32 plus the compression type byte, meaning the
XXH32/64 checksums for >=4GB block would not match about 255/256 times.

While touching this code, I refactored to consolidate redundant
implementations, improving diagnostics and performance tracking in some
cases. Also used less confusing language in those diagnostics.

Makes https://github.com/facebook/rocksdb/issues/6875 obsolete.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6978

Test Plan:
I was able to write a test for this using an SST file writer
and VerifyChecksum in a reader. The test fails before the fix, though
I'm leaving the test disabled because I don't think it's worth the
expense of running regularly.

Reviewed By: gg814

Differential Revision: D22143260

Pulled By: pdillinger

fbshipit-source-id: 982993d16134e8c50bea2269047f901c1783726e
2020-06-19 16:18:24 -07:00
sdong 223b57eeb8 Fix the bug that compressed cache is disabled in read-only DBs (#6990)
Summary:
Compressed block cache is disabled in https://github.com/facebook/rocksdb/pull/4650 for no good reason. Re-enable it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6990

Test Plan: Add a unit test to make sure a general function works with read-only DB + compressed block cache.

Reviewed By: ltamasi

Differential Revision: D22072755

fbshipit-source-id: 2a55df6363de23a78979cf6c747526359e5dc7a1
2020-06-17 14:30:54 -07:00
Zhen Li 9c24a5cb4d Fix persistent cache on windows (#6932)
Summary:
Persistent cache feature caused rocks db crash on windows. I posted a issue for it, https://github.com/facebook/rocksdb/issues/6919. I found this is because no "persistent_cache_key_prefix" is generated for persistent cache. Looking repo history, "GetUniqueIdFromFile" is not implemented on Windows. So my fix is adding "NewId()" function in "persistent_cache" and using it to generate prefix for persistent cache. In this PR, i also re-enable related test cases defined in "db_test2" and "persistent_cache_test" for windows.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6932

Test Plan:
1. run related test cases in "db_test2" and "persistent_cache_test" on windows and see it passed.
2. manually run db_bench.exe with "read_cache_path" and verified.

Reviewed By: riversand963

Differential Revision: D21911608

Pulled By: cheng-chang

fbshipit-source-id: cdfd938d54a385edbb2836b13aaa1d39b0a6f1c2
2020-06-13 13:28:31 -07:00
Andrew Kryczka 02db03af8d make L0 index/filter pinned memory usage predictable (#6911)
Summary:
Memory pinned by `pin_l0_filter_and_index_blocks_in_cache` needs to be predictable based on user config. This PR makes sure
we do not pin extra memory for large files generated by intra-L0 (see https://github.com/facebook/rocksdb/issues/6889).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6911

Test Plan: unit test

Reviewed By: siying

Differential Revision: D21835818

Pulled By: ajkr

fbshipit-source-id: a11a088549d06bed8aacc2548d266e5983f0ead4
2020-06-09 16:51:23 -07:00
anand76 98b0cbea88 Check iterator status BlockBasedTableReader::VerifyChecksumInBlocks() (#6909)
Summary:
The ```for``` loop in ```VerifyChecksumInBlocks``` only checks ```index_iter->Valid()``` which could be ```false``` either due to reaching the end of the index or, in case of partitioned index, it could be due to a checksum mismatch error when reading a 2nd level index block. Instead of throwing away the index iterator status, we need to return any errors back to the caller.

Tests:
Add a test in block_based_table_reader_test.cc.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6909

Reviewed By: pdillinger

Differential Revision: D21833922

Pulled By: anand1976

fbshipit-source-id: bc778ebf1121dbbdd768689de5183f07a9f0beae
2020-06-05 11:08:25 -07:00
Peter Dillinger 14eca6bf04 For ApproximateSizes, pro-rate table metadata size over data blocks (#6784)
Summary:
The implementation of GetApproximateSizes was inconsistent in
its treatment of the size of non-data blocks of SST files, sometimes
including and sometimes now. This was at its worst with large portion
of table file used by filters and querying a small range that crossed
a table boundary: the size estimate would include large filter size.

It's conceivable that someone might want only to know the size in terms
of data blocks, but I believe that's unlikely enough to ignore for now.
Similarly, there's no evidence the internal function AppoximateOffsetOf
is used for anything other than a one-sided ApproximateSize, so I intend
to refactor to remove redundancy in a follow-up commit.

So to fix this, GetApproximateSizes (and implementation details
ApproximateSize and ApproximateOffsetOf) now consistently include in
their returned sizes a portion of table file metadata (incl filters
and indexes) based on the size portion of the data blocks in range. In
other words, if a key range covers data blocks that are X% by size of all
the table's data blocks, returned approximate size is X% of the total
file size. It would technically be more accurate to attribute metadata
based on number of keys, but that's not computationally efficient with
data available and rarely a meaningful difference.

Also includes miscellaneous comment improvements / clarifications.

Also included is a new approximatesizerandom benchmark for db_bench.
No significant performance difference seen with this change, whether ~700 ops/sec with cache_index_and_filter_blocks and small cache or ~150k ops/sec without cache_index_and_filter_blocks.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6784

Test Plan:
Test added to DBTest.ApproximateSizesFilesWithErrorMargin.
Old code running new test...

    [ RUN      ] DBTest.ApproximateSizesFilesWithErrorMargin
    db/db_test.cc:1562: Failure
    Expected: (size) <= (11 * 100), actual: 9478 vs 1100

Other tests updated to reflect consistent accounting of metadata.

Reviewed By: siying

Differential Revision: D21334706

Pulled By: pdillinger

fbshipit-source-id: 6f86870e45213334fedbe9c73b4ebb1d8d611185
2020-06-02 12:30:23 -07:00
sdong 298b00a396 Reduce dependency on gtest dependency in release code (#6907)
Summary:
Release code now depends on gtest, indirectly through including "test_util/testharness.h". This creates multiple problems. One important reason is the definition of IGNORE_STATUS_IF_ERROR() in test_util/testharness.h. Move it to sync_point.h instead.
Note that utilities/cassandra/format.h still depends on "test_util/testharness.h". This will be resolved in a separate diff.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6907

Test Plan: Run all existing tests.

Reviewed By: ajkr

Differential Revision: D21829884

fbshipit-source-id: 9253c19ffde2936f3ae68998210f8e54f645a6e6
2020-06-02 12:11:24 -07:00
anand76 66942e8158 Avoid unnecessary reads of uncompression dictionary in MultiGet (#6906)
Summary:
We may sometimes read the uncompression dictionary when its not
necessary, when we lookup a key in an SST file but the index indicates
the key is not present. This can happen with index_type 3.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6906

Test Plan: make check

Reviewed By: cheng-chang

Differential Revision: D21828944

Pulled By: anand1976

fbshipit-source-id: 7aef4f0a39548d0874eafefd2687006d2652f9bb
2020-06-01 19:43:37 -07:00
Cheng Chang bcb9e41080 Explicitly free allocated buffer when status is not ok (#6903)
Summary:
Currently we rely on `BlockContents` to implicitly free the allocated scratch buffer, but when IO error happens, it doesn't make sense to construct the `BlockContents` which might be corrupted. In the stress test, we find that `assert(req.result.size() == block_size(handle));` fails because of potential IO errors.

In this PR, we explicitly free the scratch buffer on error without constructing `BlockContents`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6903

Test Plan: watch stress test

Reviewed By: anand1976

Differential Revision: D21823869

Pulled By: cheng-chang

fbshipit-source-id: 5603fc80e9bf3f44a9d7250ddebd871afe1eb89f
2020-06-01 15:19:40 -07:00
Cheng Chang 82a82c76e7 Fix potential memory leak of scratch buffer (#6879)
Summary:
If `req.scratch` is an internally allocated buffer, but `raw_block_contents` is not constructed to own `req.scratch`, then `req.scratch` will be leaked.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6879

Test Plan: make asan_check

Reviewed By: anand1976

Differential Revision: D21728498

Pulled By: cheng-chang

fbshipit-source-id: 8fc6a4f2543918c565ddc16ecfad1807eb9a42cf
2020-05-26 15:29:04 -07:00
Cheng Chang 91b7553293 Enable IO Uring in MultiGet in direct IO mode (#6815)
Summary:
Currently, in direct IO mode, `MultiGet` retrieves the data blocks one by one instead of in parallel, see `BlockBasedTable::RetrieveMultipleBlocks`.

Since direct IO is supported in `RandomAccessFileReader::MultiRead` in https://github.com/facebook/rocksdb/pull/6446, this PR applies `MultiRead` to `MultiGet` so that the data blocks can be retrieved in parallel.

Also, in direct IO mode and when data blocks are compressed and need to uncompressed, this PR only allocates one continuous aligned buffer to hold the data blocks, and then directly uncompress the blocks to insert into block cache, there is no longer intermediate copies to scratch buffers.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6815

Test Plan:
1. added a new unit test `BlockBasedTableReaderTest::MultiGet`.
2. existing unit tests and stress tests  contain tests against `MultiGet` in direct IO mode.

Reviewed By: anand1976

Differential Revision: D21426347

Pulled By: cheng-chang

fbshipit-source-id: b8446ae0e74152444ef9111e97f8e402ac31b24f
2020-05-14 23:26:26 -07:00
sdong 4a4b8a1344 sst_dump to reduce number of file reads (#6836)
Summary:
sst_dump can issue many file reads from the file system. This doesn't work well with file systems without a OS cache, especially remote file systems. In order to mitigate this problem, several improvements are done:
1. --readahead_size is added, so that users can specify readahead size when scanning the data.
2. Force a 512KB tail readahead, which prevents three I/Os for footer, meta index and property blocks and hopefully index and filter blocks too.
3. Consoldiate SSTDump's I/Os before opening the file for read. Use the same file prefetch buffer.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6836

Test Plan: Add a test that covers this new feature.

Reviewed By: pdillinger

Differential Revision: D21516607

fbshipit-source-id: 3ae43526286f67b2f4a5bdedfbc92719d579b87e
2020-05-12 18:23:33 -07:00
Peter Dillinger b27a1448b6 Fix false NotFound from batched MultiGet with kHashSearch (#6821)
Summary:
The error is assigning KeyContext::s to NotFound status in a
table reader for a "not found in this table" case, which skips searching
in later tables, like only a delete should. (The hash search index iterator
is the only one that can return status NotFound even if Valid() == false.)

This was detected by intermittent failure in
MultiThreadedDBTest.MultiThreaded/5, a kHashSearch configuration.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6821

Test Plan: modified existing unit test to reproduce problem

Reviewed By: anand1976

Differential Revision: D21450469

Pulled By: pdillinger

fbshipit-source-id: 7478003684d637dbd491cdac81468041a791be2c
2020-05-07 15:41:37 -07:00
anand76 ab13d43e1d Pass a timeout to FileSystem for random reads (#6751)
Summary:
Calculate ```IOOptions::timeout``` using ```ReadOptions::deadline``` and pass it to ```FileSystem::Read/FileSystem::MultiRead```. This allows us to impose a tighter bound on the time taken by Get/MultiGet on FileSystem/Envs that support IO timeouts. Even on those that don't support, check in ```RandomAccessFileReader::Read``` and ```MultiRead``` and return ```Status::TimedOut()``` if the deadline is exceeded.

For now, TableReader creation, which might do file opens and reads, are not covered. It will be implemented in another PR.

Tests:
Update existing unit tests to verify the correct timeout value is being passed
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6751

Reviewed By: riversand963

Differential Revision: D21285631

Pulled By: anand1976

fbshipit-source-id: d89af843e5a91ece866e87aa29438b52a65a8567
2020-04-30 14:50:39 -07:00
Peter Dillinger bae6f58696 Basic MultiGet support for partitioned filters (#6757)
Summary:
In MultiGet, access each applicable filter partition only once
per batch, rather than for each applicable key. Also,

* Fix Bloom stats for MultiGet
* Fix/refactor MultiGetContext::Range::KeysLeft, including
* Add efficient BitsSetToOne implementation
* Assert that MultiGetContext::Range does not go beyond shift range

Performance test: Generate db:

    $ ./db_bench --benchmarks=fillrandom --num=15000000 --cache_index_and_filter_blocks -bloom_bits=10 -partition_index_and_filters=true
    ...

Before (middle performing run of three; note some missing Bloom stats):

    $ ./db_bench --use-existing-db --benchmarks=multireadrandom --num=15000000 --cache_index_and_filter_blocks --bloom_bits=10 --threads=16 --cache_size=20000000 -partition_index_and_filters -batch_size=32 -multiread_batched -statistics --duration=20 2>&1 | egrep 'micros/op|block.cache.filter.hit|bloom.filter.(full|use)|number.multiget'
    multireadrandom :      26.403 micros/op 597517 ops/sec; (548427 of 671968 found)
    rocksdb.block.cache.filter.hit COUNT : 83443275
    rocksdb.bloom.filter.useful COUNT : 0
    rocksdb.bloom.filter.full.positive COUNT : 0
    rocksdb.bloom.filter.full.true.positive COUNT : 7931450
    rocksdb.number.multiget.get COUNT : 385984
    rocksdb.number.multiget.keys.read COUNT : 12351488
    rocksdb.number.multiget.bytes.read COUNT : 793145000
    rocksdb.number.multiget.keys.found COUNT : 7931450

After (middle performing run of three):

    $ ./db_bench_new --use-existing-db --benchmarks=multireadrandom --num=15000000 --cache_index_and_filter_blocks --bloom_bits=10 --threads=16 --cache_size=20000000 -partition_index_and_filters -batch_size=32 -multiread_batched -statistics --duration=20 2>&1 | egrep 'micros/op|block.cache.filter.hit|bloom.filter.(full|use)|number.multiget'
    multireadrandom :      21.024 micros/op 752963 ops/sec; (705188 of 863968 found)
    rocksdb.block.cache.filter.hit COUNT : 49856682
    rocksdb.bloom.filter.useful COUNT : 45684579
    rocksdb.bloom.filter.full.positive COUNT : 10395458
    rocksdb.bloom.filter.full.true.positive COUNT : 9908456
    rocksdb.number.multiget.get COUNT : 481984
    rocksdb.number.multiget.keys.read COUNT : 15423488
    rocksdb.number.multiget.bytes.read COUNT : 990845600
    rocksdb.number.multiget.keys.found COUNT : 9908456

So that's about 25% higher throughput even for random keys
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6757

Test Plan: unit test included

Reviewed By: anand1976

Differential Revision: D21243256

Pulled By: pdillinger

fbshipit-source-id: 5644a1468d9e8c8575be02f4e04bc5d62dbbb57f
2020-04-28 14:49:34 -07:00
Peter Dillinger 249eff0f30 Stats for redundant insertions into block cache (#6681)
Summary:
Since read threads do not coordinate on loading data into block
cache, two threads between Lookup and Insert can end up loading and
inserting the same data. This is particularly concerning with
cache_index_and_filter_blocks since those are hot and more likely to
be race targets if ejected from (or not pre-populated in) the cache.

Particularly with moves toward disaggregated / network storage, the cost
of redundant retrieval might be high, and we should at least have some
hard statistics from which we can estimate impact.

Example with full filter thrashing "cliff":

    $ ./db_bench --benchmarks=fillrandom --num=15000000 --cache_index_and_filter_blocks -bloom_bits=10
    ...
    $ ./db_bench --db=/tmp/rocksdbtest-172704/dbbench --use_existing_db --benchmarks=readrandom,stats --num=200000 --cache_index_and_filter_blocks --cache_size=$((130 * 1024 * 1024)) --bloom_bits=10 --threads=16 -statistics 2>&1 | egrep '^rocksdb.block.cache.(.*add|.*redundant)' | grep -v compress | sort
    rocksdb.block.cache.add COUNT : 14181
    rocksdb.block.cache.add.failures COUNT : 0
    rocksdb.block.cache.add.redundant COUNT : 476
    rocksdb.block.cache.data.add COUNT : 12749
    rocksdb.block.cache.data.add.redundant COUNT : 18
    rocksdb.block.cache.filter.add COUNT : 1003
    rocksdb.block.cache.filter.add.redundant COUNT : 217
    rocksdb.block.cache.index.add COUNT : 429
    rocksdb.block.cache.index.add.redundant COUNT : 241
    $ ./db_bench --db=/tmp/rocksdbtest-172704/dbbench --use_existing_db --benchmarks=readrandom,stats --num=200000 --cache_index_and_filter_blocks --cache_size=$((120 * 1024 * 1024)) --bloom_bits=10 --threads=16 -statistics 2>&1 | egrep '^rocksdb.block.cache.(.*add|.*redundant)' | grep -v compress | sort
    rocksdb.block.cache.add COUNT : 1182223
    rocksdb.block.cache.add.failures COUNT : 0
    rocksdb.block.cache.add.redundant COUNT : 302728
    rocksdb.block.cache.data.add COUNT : 31425
    rocksdb.block.cache.data.add.redundant COUNT : 12
    rocksdb.block.cache.filter.add COUNT : 795455
    rocksdb.block.cache.filter.add.redundant COUNT : 130238
    rocksdb.block.cache.index.add COUNT : 355343
    rocksdb.block.cache.index.add.redundant COUNT : 172478
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6681

Test Plan: Some manual testing (above) and unit test covering key metrics is included

Reviewed By: ltamasi

Differential Revision: D21134113

Pulled By: pdillinger

fbshipit-source-id: c11497b5f00f4ffdfe919823904e52d0a1a91d87
2020-04-27 13:20:27 -07:00
anand76 9e7b7e2c08 Silence false alarms in db_stress fault injection (#6741)
Summary:
False alarms are caused by codepaths that intentionally swallow IO
errors.

Tests:
make crash_test
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6741

Reviewed By: ltamasi

Differential Revision: D21181138

Pulled By: anand1976

fbshipit-source-id: 5ccfbc68eb192033488de6269e59c00f2c65ce00
2020-04-24 13:06:12 -07:00
Ibrahim Jarif ae77880223 Fix some typos in code comments (#6733)
Summary:
This PR fixes some typos in code comments.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6733

Reviewed By: siying

Differential Revision: D21209037

Pulled By: zhichao-cao

fbshipit-source-id: d9274611fab1f5e992998c8c4117b8078c4cbc69
2020-04-23 12:28:49 -07:00
mrambacher 4cbc19d2a1 Add a ConfigOptions for use in comparing objects and converting to/from strings (#6389)
Summary:
The methods in convenience.h are used to compare/convert objects to/from strings.  There is a mishmash of parameters in use here with more needed in the future.  This PR replaces those parameters with a single structure.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6389

Reviewed By: siying

Differential Revision: D21163707

Pulled By: zhichao-cao

fbshipit-source-id: f807b4cc7e2b0af3871536b69546b2604dfa81bd
2020-04-21 17:38:17 -07:00
Peter Dillinger 31da5e34c1 C++20 compatibility (#6697)
Summary:
Based on https://github.com/facebook/rocksdb/issues/6648 (CLA Signed), but heavily modified / extended:

* Implicit capture of this via [=] deprecated in C++20, and [=,this] not standard before C++20 -> now using explicit capture lists
* Implicit copy operator deprecated in gcc 9 -> add explicit '= default' definition
* std::random_shuffle deprecated in C++17 and removed in C++20 -> migrated to a replacement in RocksDB random.h API
* Add the ability to build with different std version though -DCMAKE_CXX_STANDARD=11/14/17/20 on the cmake command line
* Minimal rebuild flag of MSVC is deprecated and is forbidden with /std:c++latest (C++20)
* Added MSVC 2019 C++11 & MSVC 2019 C++20 in AppVeyor
* Added GCC 9 C++11 & GCC9 C++20 in Travis
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6697

Test Plan: make check and CI

Reviewed By: cheng-chang

Differential Revision: D21020318

Pulled By: pdillinger

fbshipit-source-id: 12311be5dbd8675a0e2c817f7ec50fa11c18ab91
2020-04-20 13:24:25 -07:00
Mike Kolupaev e45673dece Properly report IO errors when IndexType::kBinarySearchWithFirstKey is used (#6621)
Summary:
Context: Index type `kBinarySearchWithFirstKey` added the ability for sst file iterator to sometimes report a key from index without reading the corresponding data block. This is useful when sst blocks are cut at some meaningful boundaries (e.g. one block per key prefix), and many seeks land between blocks (e.g. for each prefix, the ranges of keys in different sst files are nearly disjoint, so a typical seek needs to read a data block from only one file even if all files have the prefix). But this added a new error condition, which rocksdb code was really not equipped to deal with: `InternalIterator::value()` may fail with an IO error or Status::Incomplete, but it's just a method returning a Slice, with no way to report error instead. Before this PR, this type of error wasn't handled at all (an empty slice was returned), and kBinarySearchWithFirstKey implementation was considered a prototype.

Now that we (LogDevice) have experimented with kBinarySearchWithFirstKey for a while and confirmed that it's really useful, this PR is adding the missing error handling.

It's a pretty inconvenient situation implementation-wise. The error needs to be reported from InternalIterator when trying to access value. But there are ~700 call sites of `InternalIterator::value()`, most of which either can't hit the error condition (because the iterator is reading from memtable or from index or something) or wouldn't benefit from the deferred loading of the value (e.g. compaction iterator that reads all values anyway). Adding error handling to all these call sites would needlessly bloat the code. So instead I made the deferred value loading optional: only the call sites that may use deferred loading have to call the new method `PrepareValue()` before calling `value()`. The feature is enabled with a new bool argument `allow_unprepared_value` to a bunch of methods that create iterators (it wouldn't make sense to put it in ReadOptions because it's completely internal to iterators, with virtually no user-visible effect). Lmk if you have better ideas.

Note that the deferred value loading only happens for *internal* iterators. The user-visible iterator (DBIter) always prepares the value before returning from Seek/Next/etc. We could go further and add an API to defer that value loading too, but that's most likely not useful for LogDevice, so it doesn't seem worth the complexity for now.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6621

Test Plan: make -j5 check . Will also deploy to some logdevice test clusters and look at stats.

Reviewed By: siying

Differential Revision: D20786930

Pulled By: al13n321

fbshipit-source-id: 6da77d918bad3780522e918f17f4d5513d3e99ee
2020-04-15 17:40:44 -07:00
anand76 5c19a441c4 Fault injection in db_stress (#6538)
Summary:
This PR implements a fault injection mechanism for injecting errors in reads in db_stress. The FaultInjectionTestFS is used for this purpose. A thread local structure is used to track the errors, so that each db_stress thread can independently enable/disable error injection and verify observed errors against expected errors. This is initially enabled only for Get and MultiGet, but can be extended to iterator as well once its proven stable.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6538

Test Plan:
crash_test
make check

Reviewed By: riversand963

Differential Revision: D20714347

Pulled By: anand1976

fbshipit-source-id: d7598321d4a2d72bda0ced57411a337a91d87dc7
2020-04-10 17:21:26 -07:00
Levi Tamasi e6f86cfb36 Revert the recent cache deleter change (#6620)
Summary:
Revert "Use function objects as deleters in the block cache (https://github.com/facebook/rocksdb/issues/6545)"

    This reverts commit 6301dbe7a7.

    Revert "Call out the cache deleter related interface change in HISTORY.md (https://github.com/facebook/rocksdb/issues/6606)"

    This reverts commit 3a35542f86.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6620

Test Plan: `make check`

Reviewed By: zhichao-cao

Differential Revision: D20773311

Pulled By: ltamasi

fbshipit-source-id: 7637a761f718f323ef0e7da959462e8fb06e7a2b
2020-03-31 16:11:06 -07:00
Levi Tamasi 6301dbe7a7 Use function objects as deleters in the block cache (#6545)
Summary:
As the first step of reintroducing eviction statistics for the block
cache, the patch switches from using simple function pointers as deleters
to function objects implementing an interface. This will enable using
deleters that have state, like a smart pointer to the statistics object
that is to be updated when an entry is removed from the cache. For now,
the patch adds a deleter template class `SimpleDeleter`, which simply
casts the `value` pointer to its original type and calls `delete` or
`delete[]` on it as appropriate. Note: to prevent object lifecycle
issues, deleters must outlive the cache entries referring to them;
`SimpleDeleter` ensures this by using the ("leaky") Meyers singleton
pattern.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6545

Test Plan: `make asan_check`

Reviewed By: siying

Differential Revision: D20475823

Pulled By: ltamasi

fbshipit-source-id: fe354c33dd96d9bafc094605462352305449a22a
2020-03-26 16:19:58 -07:00
Mike Kolupaev 963af52f15 Fix iterator reading filter block despite read_tier == kBlockCacheTier (#6562)
Summary:
We're seeing iterators with `ReadOptions::read_tier == kBlockCacheTier` sometimes doing file reads. Stack trace:

```
rocksdb::RandomAccessFileReader::Read(unsigned long, unsigned long, rocksdb::Slice*, char*, bool) const
rocksdb::BlockFetcher::ReadBlockContents()
rocksdb::Status rocksdb::BlockBasedTable::MaybeReadBlockAndLoadToCache<rocksdb::ParsedFullFilterBlock>(rocksdb::FilePrefetchBuffer*, rocksdb::ReadOptions const&, rocksdb::BlockHandle const&, rocksdb::UncompressionDict const&, rocksdb::CachableEntry<rocksdb::ParsedFullFilterBlock>*, rocksdb::BlockType, rocksdb::GetContext*, rocksdb::BlockCacheLookupContext*, rocksdb::BlockContents*) const
rocksdb::Status rocksdb::BlockBasedTable::RetrieveBlock<rocksdb::ParsedFullFilterBlock>(rocksdb::FilePrefetchBuffer*, rocksdb::ReadOptions const&, rocksdb::BlockHandle const&, rocksdb::UncompressionDict const&, rocksdb::CachableEntry<rocksdb::ParsedFullFilterBlock>*, rocksdb::BlockType, rocksdb::GetContext*, rocksdb::BlockCacheLookupContext*, bool, bool) const
rocksdb::FilterBlockReaderCommon<rocksdb::ParsedFullFilterBlock>::ReadFilterBlock(rocksdb::BlockBasedTable const*, rocksdb::FilePrefetchBuffer*, rocksdb::ReadOptions const&, bool, rocksdb::GetContext*, rocksdb::BlockCacheLookupContext*, rocksdb::CachableEntry<rocksdb::ParsedFullFilterBlock>*)
rocksdb::FilterBlockReaderCommon<rocksdb::ParsedFullFilterBlock>::GetOrReadFilterBlock(bool, rocksdb::GetContext*, rocksdb::BlockCacheLookupContext*, rocksdb::CachableEntry<rocksdb::ParsedFullFilterBlock>*) const
rocksdb::FullFilterBlockReader::MayMatch(rocksdb::Slice const&, bool, rocksdb::GetContext*, rocksdb::BlockCacheLookupContext*) const
rocksdb::FullFilterBlockReader::RangeMayExist(rocksdb::Slice const*, rocksdb::Slice const&, rocksdb::SliceTransform const*, rocksdb::Comparator const*, rocksdb::Slice const*, bool*, bool, rocksdb::BlockCacheLookupContext*)
rocksdb::BlockBasedTable::PrefixMayMatch(rocksdb::Slice const&, rocksdb::ReadOptions const&, rocksdb::SliceTransform const*, bool, rocksdb::BlockCacheLookupContext*) const
rocksdb::BlockBasedTableIterator<rocksdb::DataBlockIter, rocksdb::Slice>::SeekImpl(rocksdb::Slice const*)
rocksdb::ForwardIterator::SeekInternal(rocksdb::Slice const&, bool)
rocksdb::DBIter::Seek(rocksdb::Slice const&)
```

`BlockBasedTableIterator::CheckPrefixMayMatch` was missing a check for `kBlockCacheTier`. This PR adds it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6562

Test Plan: deployed it to a logdevice test cluster and looked at logdevice's IO tracing.

Reviewed By: siying

Differential Revision: D20529368

Pulled By: al13n321

fbshipit-source-id: 65bf33964b1951464415c900336635fb20919611
2020-03-26 15:21:26 -07:00
Cheng Chang 4fc216649d Support direct IO in RandomAccessFileReader::MultiRead (#6446)
Summary:
By supporting direct IO in RandomAccessFileReader::MultiRead, the benefits of parallel IO (IO uring) and direct IO can be combined.

In direct IO mode, read requests are aligned and merged together before being issued to RandomAccessFile::MultiRead, so blocks in the original requests might share the same underlying buffer, the shared buffers are returned in `aligned_bufs`, which is a new parameter of the `MultiRead` API.

For example, suppose alignment requirement for direct IO is 4KB, one request is (offset: 1KB, len: 1KB), another request is (offset: 3KB, len: 1KB), then since they all belong to page (offset: 0, len: 4KB), `MultiRead` only reads the page with direct IO into a buffer on heap, and returns 2 Slices referencing regions in that same buffer. See `random_access_file_reader_test.cc` for more examples.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6446

Test Plan: Added a new test `random_access_file_reader_test.cc`.

Reviewed By: anand1976

Differential Revision: D20097518

Pulled By: cheng-chang

fbshipit-source-id: ca48a8faf9c3af146465c102ef6b266a363e78d1
2020-03-20 16:33:26 -07:00