Commit Graph

345 Commits

Author SHA1 Message Date
Cheng Chang
40497a875a Reduce memory copies when fetching and uncompressing blocks from SST files (#6689)
Summary:
In https://github.com/facebook/rocksdb/pull/6455, we modified the interface of `RandomAccessFileReader::Read` to be able to get rid of memcpy in direct IO mode.
This PR applies the new interface to `BlockFetcher` when reading blocks from SST files in direct IO mode.

Without this PR, in direct IO mode, when fetching and uncompressing compressed blocks, `BlockFetcher` will first copy the raw compressed block into `BlockFetcher::compressed_buf_` or `BlockFetcher::stack_buf_` inside `RandomAccessFileReader::Read` depending on the block size. then during uncompressing, it will copy the uncompressed block into `BlockFetcher::heap_buf_`.

In this PR, we get rid of the first memcpy and directly uncompress the block from `direct_io_buf_` to `heap_buf_`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6689

Test Plan: A new unit test `block_fetcher_test` is added.

Reviewed By: anand1976

Differential Revision: D21006729

Pulled By: cheng-chang

fbshipit-source-id: 2370b92c24075692423b81277415feb2aed5d980
2020-04-24 15:32:56 -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
Yanqin Jin
0c05624d50 Compaction with timestamp: input boundaries (#6645)
Summary:
Towards making compaction logic compatible with user timestamp.
When computing boundaries and overlapping ranges for inputs of compaction, We need to compare SSTs by user key without timestamp.

Test plan (devserver):
```
make check
```
Several individual tests:
```
./version_set_test --gtest_filter=VersionStorageInfoTimestampTest.GetOverlappingInputs
./db_with_timestamp_compaction_test
./db_with_timestamp_basic_test
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6645

Reviewed By: ltamasi

Differential Revision: D20960012

Pulled By: riversand963

fbshipit-source-id: ad377fa9eb481bf7a8a3e1824aaade48cdc653a4
2020-04-10 16:05:49 -07:00
Luca Giacchino
66a95f0fac Provide an allocator for new memory type to be used with RocksDB block cache (#6214)
Summary:
New memory technologies are being developed by various hardware vendors (Intel DCPMM is one such technology currently available). These new memory types require different libraries for allocation and management (such as PMDK and memkind). The high capacities available make it possible to provision large caches (up to several TBs in size), beyond what is achievable with DRAM.
The new allocator provided in this PR uses the memkind library to allocate memory on different media.

**Performance**

We tested the new allocator using db_bench.
- For each test, we vary the size of the block cache (relative to the size of the uncompressed data in the database).
- The database is filled sequentially. Throughput is then measured with a readrandom benchmark.
- We use a uniform distribution as a worst-case scenario.

The plot shows throughput (ops/s) relative to a configuration with no block cache and default allocator.
For all tests, p99 latency is below 500 us.

![image](https://user-images.githubusercontent.com/26400080/71108594-42479100-2178-11ea-8231-8a775bbc92db.png)

**Changes**

- Add MemkindKmemAllocator
- Add --use_cache_memkind_kmem_allocator db_bench option (to create an LRU block cache with the new allocator)
- Add detection of memkind library with KMEM DAX support
- Add test for MemkindKmemAllocator

**Minimum Requirements**

- kernel 5.3.12
- ndctl v67 - https://github.com/pmem/ndctl
- memkind v1.10.0 - https://github.com/memkind/memkind

**Memory Configuration**

The allocator uses the MEMKIND_DAX_KMEM memory kind. Follow the instructions on[ memkind’s GitHub page](https://github.com/memkind/memkind) to set up NVDIMM memory accordingly.

Note on memory allocation with NVDIMM memory exposed as system memory.
- The MemkindKmemAllocator will only allocate from NVDIMM memory (using memkind_malloc with MEMKIND_DAX_KMEM kind).
- The default allocator is not restricted to RAM by default. Based on NUMA node latency, the kernel should allocate from local RAM preferentially, but it’s a kernel decision. numactl --preferred/--membind can be used to allocate preferentially/exclusively from the local RAM node.

**Usage**

When creating an LRU cache, pass a MemkindKmemAllocator object as argument.
For example (replace capacity with the desired value in bytes):

```
#include "rocksdb/cache.h"
#include "memory/memkind_kmem_allocator.h"

NewLRUCache(
    capacity /*size_t*/,
    6 /*cache_numshardbits*/,
    false /*strict_capacity_limit*/,
    false /*cache_high_pri_pool_ratio*/,
    std::make_shared<MemkindKmemAllocator>());
```

Refer to [RocksDB’s block cache documentation](https://github.com/facebook/rocksdb/wiki/Block-Cache) to assign the LRU cache as block cache for a database.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6214

Reviewed By: cheng-chang

Differential Revision: D19292435

fbshipit-source-id: 7202f47b769e7722b539c86c2ffd669f64d7b4e1
2020-04-09 20:47:23 -07:00
Cheng Chang
d648a0e17f Add unit test for TransactionLockMgr (#6599)
Summary:
Although there are tests related to locking in transaction_test, this new test directly tests against TransactionLockMgr.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6599

Test Plan: make transaction_lock_mgr_test && ./transaction_lock_mgr_test

Reviewed By: lth

Differential Revision: D20673749

Pulled By: cheng-chang

fbshipit-source-id: 1fa4a13218e68d785f5a99924556751a8c5c0f31
2020-04-08 13:51:51 -07:00
Sagar Vemuri
0355d14dd9 Add a simple timer support to schedule work at fixed times/intervals (#6543)
Summary:
Adding a simple timer support to schedule work at a fixed time.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6543

Test Plan: TODO: clean up the unit tests, and make them better.

Reviewed By: siying

Differential Revision: D20465390

Pulled By: sagar0

fbshipit-source-id: cba143f70b6339863e1d0f8b8bf92e51c2b3d678
2020-04-07 11:55:27 -07:00
Ziyue Yang
03a781a90c Add pipelined & parallel compression optimization (#6262)
Summary:
This PR adds support for pipelined & parallel compression optimization for `BlockBasedTableBuilder`. This optimization makes block building, block compression and block appending a pipeline, and uses multiple threads to accelerate block compression. Users can set `CompressionOptions::parallel_threads` greater than 1 to enable compression parallelism.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6262

Reviewed By: ajkr

Differential Revision: D20651306

fbshipit-source-id: 62125590a9c15b6d9071def9dc72589c1696a4cb
2020-04-01 16:40:18 -07:00
Levi Tamasi
6f62322fe4 Add blob files to VersionStorageInfo/VersionBuilder (#6597)
Summary:
The patch adds a couple of classes to represent metadata about
blob files: `SharedBlobFileMetaData` contains the information elements
that are immutable (once the blob file is closed), e.g. blob file number,
total number and size of blob files, checksum method/value, while
`BlobFileMetaData` contains attributes that can vary across versions like
the amount of garbage in the file. There is a single `SharedBlobFileMetaData`
for each blob file, which is jointly owned by the `BlobFileMetaData` objects
that point to it; `BlobFileMetaData` objects, in turn, are owned by `Version`s
and can also be shared if the (immutable _and_ mutable) state of the blob file
is the same in two versions.

In addition, the patch adds the blob file metadata to `VersionStorageInfo`, and extends
`VersionBuilder` so that it can apply blob file related `VersionEdit`s (i.e. those
containing `BlobFileAddition`s and/or `BlobFileGarbage`), and save blob file metadata
to a new `VersionStorageInfo`. Consistency checks are also extended to ensure
that table files point to blob files that are part of the `Version`, and that all blob files
that are part of any given `Version` have at least some _non_-garbage data in them.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6597

Test Plan: `make check`

Reviewed By: riversand963

Differential Revision: D20656803

Pulled By: ltamasi

fbshipit-source-id: f1f74d135045b3b42d0146f03ee576ef0a4bfd80
2020-03-26 18:51:53 -07:00
Yanqin Jin
fb09ef05dc Attempt to recover from db with missing table files (#6334)
Summary:
There are situations when RocksDB tries to recover, but the db is in an inconsistent state due to SST files referenced in the MANIFEST being missing. In this case, previous RocksDB will just fail the recovery and return a non-ok status.
This PR enables another possibility. During recovery, RocksDB checks possible MANIFEST files, and try to recover to the most recent state without missing table file. `VersionSet::Recover()` applies version edits incrementally and "materializes" a version only when this version does not reference any missing table file. After processing the entire MANIFEST, the version created last will be the latest version.
`DBImpl::Recover()` calls `VersionSet::Recover()`. Afterwards, WAL replay will *not* be performed.
To use this capability, set `options.best_efforts_recovery = true` when opening the db. Best-efforts recovery is currently incompatible with atomic flush.

Test plan (on devserver):
```
$make check
$COMPILE_WITH_ASAN=1 make all && make check
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6334

Reviewed By: anand1976

Differential Revision: D19778960

Pulled By: riversand963

fbshipit-source-id: c27ea80f29bc952e7d3311ecf5ee9c54393b40a8
2020-03-20 19:30:48 -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
sdong
8ad4b32c5d cmake: add option WITH_CORE_TOOLS to exclude tools except ldb and sst_dump (#6506)
Summary:
ldb and sst_dump are most important tools and they don't dependend on gflags. In cmake, we don't have an way to only build these two tools and exclude other tools. This is inconvenient if the environment has a problem with gflags. Add such an option WITH_CORE_TOOLS.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6506

Test Plan: cmake and build with WITH_TOOLS and without.

Differential Revision: D20473029

fbshipit-source-id: 3d730fd14bbae6eeeae7f9cc9aec50a4e488ad72
2020-03-18 11:01:38 -07:00
sdong
d66908091d De-template block based table iterator (#6531)
Summary:
Right now block based table iterator is used as both of iterating data for block based table, and for the index iterator for partitioend index. This was initially convenient for introducing a new iterator and block type for new index format, while reducing code change. However, these two usage doesn't go with each other very well. For example, Prev() is never called for partitioned index iterator, and some other complexity is maintained in block based iterators, which is not needed for index iterator but maintainers will always need to reason about it. Furthermore, the template usage is not following Google C++ Style which we are following, and makes a large chunk of code tangled together. This commit separate the two iterators. Right now, here is what it is done:
1. Copy the block based iterator code into partitioned index iterator, and de-template them.
2. Remove some code not needed for partitioned index. The upper bound check and tricks are removed. We never tested performance for those tricks when partitioned index is enabled in the first place. It's unlikelyl to generate performance regression, as creating new partitioned index block is much rarer than data blocks.
3. Separate out the prefetch logic to a helper class and both classes call them.

This commit will enable future follow-ups. One direction is that we might separate index iterator interface for data blocks and index blocks, as they are quite different.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6531

Test Plan: build using make and cmake. And build release

Differential Revision: D20473108

fbshipit-source-id: e48011783b339a4257c204cc07507b171b834b0f
2020-03-16 12:20:50 -07:00
Zhichao Cao
a824727db4 Fix build bug caused by PR 6516 (#6535)
Summary:
Fix the build corruption caused by PR https://github.com/facebook/rocksdb/issues/6516

Testing plan: make make asan_check
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6535

Differential Revision: D20448614

Pulled By: zhichao-cao

fbshipit-source-id: 4d2a3dae6cdd781fcfe8e28a84ac3f536db1b067
2020-03-13 16:48:03 -07:00
Zhichao Cao
5c30e6c088 Separate timestamp related test from db_basic_test (#6516)
Summary:
In some of the test, db_basic_test may cause time out due to its long running time. Separate the timestamp related test from db_basic_test to avoid the potential issue.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6516

Test Plan: pass make asan_check

Differential Revision: D20423922

Pulled By: zhichao-cao

fbshipit-source-id: d6306f89a8de55b07bf57233e4554c09ef1fe23a
2020-03-13 11:37:15 -07:00
sdong
674cf41732 Divide block_based_table_reader.cc (#6527)
Summary:
block_based_table_reader.cc is a giant file, which makes it hard for users to navigate the code. Divide the files to multiple files.
Some class templates cannot be moved to .cc file. They are moved to .h files. It is still better than including them all in block_based_table_reader.cc.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6527

Test Plan: "make all check" and "make release". Also build using cmake.

Differential Revision: D20428455

fbshipit-source-id: ca713c698469f07f35bc0c271358c0874ed4eb28
2020-03-12 21:41:50 -07:00
Levi Tamasi
c15e85bdcb Move BlobDB related files under db/ to db/blob/ (#6519)
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/6519

Test Plan:
```
make all
make check
```

Differential Revision: D20400691

Pulled By: ltamasi

fbshipit-source-id: 20ef911cf1c2c92c7f71ef0b493f9be64f2eef94
2020-03-12 11:00:56 -07:00
Cheng Chang
2d9efc9ab2 Cache result of GetLogicalBufferSize in Linux (#6457)
Summary:
In Linux, when reopening DB with many SST files, profiling shows that 100% system cpu time spent for a couple of seconds for `GetLogicalBufferSize`. This slows down MyRocks' recovery time when site is down.

This PR introduces two new APIs:
1. `Env::RegisterDbPaths` and `Env::UnregisterDbPaths` lets `DB` tell the env when it starts or stops using its database directories . The `PosixFileSystem` takes this opportunity to set up a cache from database directories to the corresponding logical block sizes.
2. `LogicalBlockSizeCache` is defined only for OS_LINUX to cache the logical block sizes.

Other modifications:
1. rename `logical buffer size` to `logical block size` to be consistent with Linux terms.
2. declare `GetLogicalBlockSize` in `PosixHelper` to expose it to `PosixFileSystem`.
3. change the functions `IOError` and `IOStatus` in `env/io_posix.h` to have external linkage since they are used in other translation units too.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6457

Test Plan:
1. A new unit test is added for `LogicalBlockSizeCache` in `env/io_posix_test.cc`.
2. A new integration test is added for `DB` operations related to the cache in `db/db_logical_block_size_cache_test.cc`.

`make check`

Differential Revision: D20131243

Pulled By: cheng-chang

fbshipit-source-id: 3077c50f8065c0bffb544d8f49fb10bba9408d04
2020-03-11 18:40:05 -07:00
Adam Retter
8fc20ac468 Add ppc64le builds to Travis (#6144)
Summary:
Let's see how this goes...
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6144

Differential Revision: D20387515

Pulled By: pdillinger

fbshipit-source-id: ba2669348c267141dfddff910b4c2224a22cbb38
2020-03-11 12:33:45 -07:00
Levi Tamasi
f5bc3b99d5 Split BlobFileState into an immutable and a mutable part (#6502)
Summary:
It's never too soon to refactor something. The patch splits the recently
introduced (`VersionEdit` related) `BlobFileState` into two classes
`BlobFileAddition` and `BlobFileGarbage`. The idea is that once blob files
are closed, they are immutable, and the only thing that changes is the
amount of garbage in them. In the new design, `BlobFileAddition` contains
the immutable attributes (currently, the count and total size of all blobs, checksum
method, and checksum value), while `BlobFileGarbage` contains the mutable
GC-related information elements (count and total size of garbage blobs). This is a
better fit for the GC logic and is more consistent with how SST files are handled.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6502

Test Plan: `make check`

Differential Revision: D20348352

Pulled By: ltamasi

fbshipit-source-id: ff93f0121e80ab15e0e0a6525ba0d6af16a0e008
2020-03-10 17:27:26 -07:00
Zhichao Cao
e62fe50634 Introduce FaultInjectionTestFS to test fault File system instead of Env (#6414)
Summary:
In the current code base, we can use FaultInjectionTestEnv to simulate the env issue such as file write/read errors, which are used in most of the test. The PR https://github.com/facebook/rocksdb/issues/5761 introduce the File System as a new Env API. This PR implement the FaultInjectionTestFS, which can be used to simulate when File System has issues such as IO error. user can specify any IOStatus error as input, such that FS corresponding actions will return certain error to the caller.

A set of ErrorHandlerFSTests are introduced for testing
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6414

Test Plan: pass make asan_check, pass error_handler_fs_test.

Differential Revision: D20252421

Pulled By: zhichao-cao

fbshipit-source-id: e922038f8ce7e6d1da329fd0bba7283c4b779a21
2020-03-04 12:35:05 -08:00
Fabrice Fontaine
8bbd76edbf Check for sys/auxv.h (#6359)
Summary:
Check for sys/auxv.h and getauxval before using them as they are not
always available (for example on uclibc)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6359

Differential Revision: D20239797

fbshipit-source-id: 175a098094d81545628c2372e7c388e70a32fd48
2020-03-03 18:09:59 -08:00
Levi Tamasi
d87c10c6ab Add blob file state to VersionEdit (#6416)
Summary:
BlobDB currently does not keep track of blob files: no records are written to
the manifest when a blob file is added or removed, and upon opening a database,
the list of blob files is populated simply based on the contents of the blob directory.
This means that lost blob files cannot be detected at the moment. We plan to solve
this issue by making blob files a part of `Version`; as a first step, this patch makes
it possible to store information about blob files in `VersionEdit`. Currently, this information
includes blob file number, total number and size of all blobs, and total number and size
of garbage blobs. However, the format is extensible: new fields can be added in
both a forward compatible and a forward incompatible manner if needed (similarly
to `kNewFile4`).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6416

Test Plan: `make check`

Differential Revision: D19894234

Pulled By: ltamasi

fbshipit-source-id: f9753e1f2aedf6dadb70c09b345207cb9c58c329
2020-02-24 18:39:53 -08:00
Cheng Chang
dafb568052 Add utility class Defer (#6382)
Summary:
Add a utility class `Defer` to defer the execution of a function until the Defer object goes out of scope.
Used in VersionSet:: ProcessManifestWrites as an example.
The inline comments for class `Defer` have more details.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6382

Test Plan: `make defer_test version_set_test && ./defer_test && ./version_set_test`

Differential Revision: D19797538

Pulled By: cheng-chang

fbshipit-source-id: b1a9b7306e4fd4f48ec2ab55783caa561a315f0f
2020-02-10 17:59:47 -08:00
Zhichao Cao
4369f2c7bb Checksum for each SST file and stores in MANIFEST (#6216)
Summary:
In the current code base, RocksDB generate the checksum for each block and verify the checksum at usage. Current PR enable SST file checksum. After a SST file is generated by Flush or Compaction, RocksDB generate the SST file checksum and store the checksum value and checksum method name in the vs_info and MANIFEST as part for the FileMetadata.

Added the enable_sst_file_checksum to Options to enable or disable file checksum. Added sst_file_checksum to Options such that user can plugin their own SST file checksum calculate method via overriding the SstFileChecksum class. The checksum information inlcuding uint32_t checksum value and a checksum name (string).  A new tool is added to LDB such that user can dump out a list of file checksum information from MANIFEST. If user enables the file checksum but does not provide the sst_file_checksum instance, RocksDB will use the default crc32checksum implemented in table/sst_file_checksum_crc32c.h
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6216

Test Plan: Added the testing case in table_test and ldb_cmd_test to verify checksum is correct in different level. Pass make asan_check.

Differential Revision: D19171461

Pulled By: zhichao-cao

fbshipit-source-id: b2e53479eefc5bb0437189eaa1941670e5ba8b87
2020-02-10 15:52:52 -08:00
blackyblack
84b41a6969 Only add gtest target when building with tests (#6377)
Summary:
External CMAKE projects cannot add own gtest target due to CMP0002 policy. We should not add gtest target unless we build with tests.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6377

Differential Revision: D19801708

fbshipit-source-id: 662484683e8737e10397ddb0d17705da5243c4f9
2020-02-07 17:16:44 -08:00
Cheng Chang
b42fa1497f Support move semantics for PinnableSlice (#6374)
Summary:
It's logically correct for PinnableSlice to support move semantics to transfer ownership of the pinned memory region. This PR adds both move constructor and move assignment to PinnableSlice.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6374

Test Plan:
A set of unit tests for the move semantics are added in slice_test.
So `make slice_test && ./slice_test`.

Differential Revision: D19739254

Pulled By: cheng-chang

fbshipit-source-id: f898bd811bb05b2d87384ec58b645e9915e8e0b1
2020-02-07 14:26:26 -08:00
anand76
afa2420c2b Introduce a new storage specific Env API (#5761)
Summary:
The current Env API encompasses both storage/file operations, as well as OS related operations. Most of the APIs return a Status, which does not have enough metadata about an error, such as whether its retry-able or not, scope (i.e fault domain) of the error etc., that may be required in order to properly handle a storage error. The file APIs also do not provide enough control over the IO SLA, such as timeout, prioritization, hinting about placement and redundancy etc.

This PR separates out the file/storage APIs from Env into a new FileSystem class. The APIs are updated to return an IOStatus with metadata about the error, as well as to take an IOOptions structure as input in order to allow more control over the IO.

The user can set both ```options.env``` and ```options.file_system``` to specify that RocksDB should use the former for OS related operations and the latter for storage operations. Internally, a ```CompositeEnvWrapper``` has been introduced that inherits from ```Env``` and redirects individual methods to either an ```Env``` implementation or the ```FileSystem``` as appropriate. When options are sanitized during ```DB::Open```, ```options.env``` is replaced with a newly allocated ```CompositeEnvWrapper``` instance if both env and file_system have been specified. This way, the rest of the RocksDB code can continue to function as before.

This PR also ports PosixEnv to the new API by splitting it into two - PosixEnv and PosixFileSystem. PosixEnv is defined as a sub-class of CompositeEnvWrapper, and threading/time functions are overridden with Posix specific implementations in order to avoid an extra level of indirection.

The ```CompositeEnvWrapper``` translates ```IOStatus``` return code to ```Status```, and sets the severity to ```kSoftError``` if the io_status is retryable. The error handling code in RocksDB can then recover the DB automatically.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5761

Differential Revision: D18868376

Pulled By: anand1976

fbshipit-source-id: 39efe18a162ea746fabac6360ff529baba48486f
2019-12-13 14:48:41 -08:00
Peter Dillinger
58d46d1915 Add useful idioms to Random API (OneInOpt, PercentTrue) (#6154)
Summary:
And clean up related code, especially in stress test.

(More clean up of db_stress_test_base.cc coming after this.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6154

Test Plan: make check, make blackbox_crash_test for a bit

Differential Revision: D18938180

Pulled By: pdillinger

fbshipit-source-id: 524d27621b8dbb25f6dff40f1081e7c00630357e
2019-12-13 14:30:14 -08:00
Kefu Chai
ac304adf46 cmake: do not build tests for Release build and cleanups (#5916)
Summary:
fixes https://github.com/facebook/rocksdb/issues/2445
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5916

Differential Revision: D19031236

fbshipit-source-id: bc3107b6b25a01958677d7cb411b1f381aae91c6
2019-12-13 12:48:06 -08:00
Adam Retter
984b6e71d6 Add Visual Studio 2015 to AppVeyor (#5446)
Summary:
This is required to compile on Windows with Visual Studio 2015, which is used for creating the RocksJava releases.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5446

Differential Revision: D18924811

fbshipit-source-id: a183a62e79a2af5aaf59cd08235458a172fe7dcb
2019-12-10 20:02:31 -08:00
Adam Simpkins
2bb5fc1280 Add an option to the CMake build to disable building shared libraries (#6122)
Summary:
Add an option to explicitly disable building shared versions of the
RocksDB libraries.  The shared libraries cannot be built in cases where
some dependencies are only available as static libraries.  This allows
still building RocksDB in these situations.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6122

Differential Revision: D18920740

fbshipit-source-id: d24f66d93c68a1e65635e6e0b663bae62c903bca
2019-12-10 15:20:50 -08:00
sdong
7d79b32618 Break db_stress_tool.cc to a list of source files (#6134)
Summary:
db_stress_tool.cc now is a giant file. In order to main it easier to improve and maintain, break it down to multiple source files.
Most classes are turned into their own files. Separate .h and .cc files are created for gflag definiations. Another .h and .cc files are created for some common functions. Some test execution logic that is only loosely related to class StressTest is moved to db_stress_driver.h and db_stress_driver.cc. All the files are located under db_stress_tool/. The directory name is created as such because if we end it with either stress or test, .gitignore will ignore any file under it and makes it prone to issues in developements.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6134

Test Plan: Build under GCC7 with and without LITE on using GNU Make. Build with GCC 4.8. Build with cmake with -DWITH_TOOL=1

Differential Revision: D18876064

fbshipit-source-id: b25d0a7451840f31ac0f5ebb0068785f783fdf7d
2019-12-08 23:51:01 -08:00
suzanwen
bac38c992a Isolate building db_bench from tests with WITH_BENCHMARK_TOOLS option. (#6098)
Summary:
Isolate `db_bench` from building tests, out of respect for the related comments.
Let building tests yields to `WITH_TEST=ON` AND `CMAKE_BUILD_TYPE=Debug` both,
and building `db_bench` yields to `WITH_BENCHMARK_TOOLS=ON`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6098

Test Plan: cmake -DCMAKE_BUILD_TYPE=Debug/Release -DWITH_TESTS=ON/OFF -DWITH_BENCHMARK_TOOLS=ON/OFF -DWITH_TOOLS=ON/OFF && make

Differential Revision: D18856891

Pulled By: riversand963

fbshipit-source-id: addbee8ad6abefb877843a313b4630cfab3ce4f0
2019-12-08 21:34:28 -08:00
John Ericson
771e1723c7 Use lowercase for shlwapi.lib rpcrt4.lib (#6076)
Summary:
This fixes MinGW cross compilation from case-sensative file systems, at no harm to MinGW builds on  Windows.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6076

Differential Revision: D18710554

fbshipit-source-id: a9f299ac3aa019f7dbc07ed0c4a79e19cf99b488
2019-11-26 13:28:32 -08:00
suzanwen
adcf920f40 Compatible changes for cmake (#6045)
Summary:
`${TESTUTILLIB}` should be linked with targets`${LIBS}`, otherwise it may not find the references. After that, we have to work fine with `${CMAKE_CURRENT_SOURCE_DIR}` in `cmake/modules/ReadVersion.cmake`, while building external projects with `add_subdirectory(/path/to/rocksdb)`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6045

Differential Revision: D18641791

Pulled By: pdillinger

fbshipit-source-id: a56b03b4dda6bae6edce1375324f51340917dddc
2019-11-22 08:19:48 -08:00
Peter Dillinger
00d58a370e Abandon use of folly::Optional (#6036)
Summary:
Had complications with LITE build and valgrind test.
Reverts/fixes small parts of PR https://github.com/facebook/rocksdb/issues/6007
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6036

Test Plan:
make LITE=1 all check
and
ROCKSDB_VALGRIND_RUN=1 DISABLE_JEMALLOC=1 make -j24 db_bloom_filter_test && ROCKSDB_VALGRIND_RUN=1 DISABLE_JEMALLOC=1 ./db_bloom_filter_test

Differential Revision: D18512238

Pulled By: pdillinger

fbshipit-source-id: 37213cf0d309edf11c483fb4b2fb6c02c2cf2b28
2019-11-14 14:04:15 -08:00
Peter Dillinger
f059c7d9b9 New Bloom filter implementation for full and partitioned filters (#6007)
Summary:
Adds an improved, replacement Bloom filter implementation (FastLocalBloom) for full and partitioned filters in the block-based table. This replacement is faster and more accurate, especially for high bits per key or millions of keys in a single filter.

Speed

The improved speed, at least on recent x86_64, comes from
* Using fastrange instead of modulo (%)
* Using our new hash function (XXH3 preview, added in a previous commit), which is much faster for large keys and only *slightly* slower on keys around 12 bytes if hashing the same size many thousands of times in a row.
* Optimizing the Bloom filter queries with AVX2 SIMD operations. (Added AVX2 to the USE_SSE=1 build.) Careful design was required to support (a) SIMD-optimized queries, (b) compatible non-SIMD code that's simple and efficient, (c) flexible choice of number of probes, and (d) essentially maximized accuracy for a cache-local Bloom filter. Probes are made eight at a time, so any number of probes up to 8 is the same speed, then up to 16, etc.
* Prefetching cache lines when building the filter. Although this optimization could be applied to the old structure as well, it seems to balance out the small added cost of accumulating 64 bit hashes for adding to the filter rather than 32 bit hashes.

Here's nominal speed data from filter_bench (200MB in filters, about 10k keys each, 10 bits filter data / key, 6 probes, avg key size 24 bytes, includes hashing time) on Skylake DE (relatively low clock speed):

$ ./filter_bench -quick -impl=2 -net_includes_hashing # New Bloom filter
Build avg ns/key: 47.7135
Mixed inside/outside queries...
  Single filter net ns/op: 26.2825
  Random filter net ns/op: 150.459
    Average FP rate %: 0.954651
$ ./filter_bench -quick -impl=0 -net_includes_hashing # Old Bloom filter
Build avg ns/key: 47.2245
Mixed inside/outside queries...
  Single filter net ns/op: 63.2978
  Random filter net ns/op: 188.038
    Average FP rate %: 1.13823

Similar build time but dramatically faster query times on hot data (63 ns to 26 ns), and somewhat faster on stale data (188 ns to 150 ns). Performance differences on batched and skewed query loads are between these extremes as expected.

The only other interesting thing about speed is "inside" (query key was added to filter) vs. "outside" (query key was not added to filter) query times. The non-SIMD implementations are substantially slower when most queries are "outside" vs. "inside". This goes against what one might expect or would have observed years ago, as "outside" queries only need about two probes on average, due to short-circuiting, while "inside" always have num_probes (say 6). The problem is probably the nastily unpredictable branch. The SIMD implementation has few branches (very predictable) and has pretty consistent running time regardless of query outcome.

Accuracy

The generally improved accuracy (re: Issue https://github.com/facebook/rocksdb/issues/5857) comes from a better design for probing indices
within a cache line (re: Issue https://github.com/facebook/rocksdb/issues/4120) and improved accuracy for millions of keys in a single filter from using a 64-bit hash function (XXH3p). Design details in code comments.

Accuracy data (generalizes, except old impl gets worse with millions of keys):
Memory bits per key: FP rate percent old impl -> FP rate percent new impl
6: 5.70953 -> 5.69888
8: 2.45766 -> 2.29709
10: 1.13977 -> 0.959254
12: 0.662498 -> 0.411593
16: 0.353023 -> 0.0873754
24: 0.261552 -> 0.0060971
50: 0.225453 -> ~0.00003 (less than 1 in a million queries are FP)

Fixes https://github.com/facebook/rocksdb/issues/5857
Fixes https://github.com/facebook/rocksdb/issues/4120

Unlike the old implementation, this implementation has a fixed cache line size (64 bytes). At 10 bits per key, the accuracy of this new implementation is very close to the old implementation with 128-byte cache line size. If there's sufficient demand, this implementation could be generalized.

Compatibility

Although old releases would see the new structure as corrupt filter data and read the table as if there's no filter, we've decided only to enable the new Bloom filter with new format_version=5. This provides a smooth path for automatic adoption over time, with an option for early opt-in.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6007

Test Plan: filter_bench has been used thoroughly to validate speed, accuracy, and correctness. Unit tests have been carefully updated to exercise new and old implementations, as well as the logic to select an implementation based on context (format_version).

Differential Revision: D18294749

Pulled By: pdillinger

fbshipit-source-id: d44c9db3696e4d0a17caaec47075b7755c262c5f
2019-11-13 16:44:01 -08:00
Peter Dillinger
ec11eff3bc FilterPolicy consolidation, part 2/2 (#5966)
Summary:
The parts that are used to implement FilterPolicy /
NewBloomFilterPolicy and not used other than for the block-based table
should be consolidated under table/block_based/filter_policy*.

This change is step 2 of 2:
mv util/bloom.cc table/block_based/filter_policy.cc
This gets its own PR so that git has the best chance of following the
rename for blame purposes. Note that low-level shared implementation
details of Bloom filters remain in util/bloom_impl.h, and
util/bloom_test.cc remains where it is for now.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5966

Test Plan: make check

Differential Revision: D18124930

Pulled By: pdillinger

fbshipit-source-id: 823bc09025b3395f092ef46a46aa5ba92a914d84
2019-10-24 15:44:51 -07:00
Peter Dillinger
dd19014a7a FilterPolicy consolidation, part 1/2 (#5963)
Summary:
The parts that are used to implement FilterPolicy /
NewBloomFilterPolicy and not used other than for the block-based table
should be consolidated under table/block_based/filter_policy*. I don't
foresee sharing these APIs with e.g. the Plain Table because they don't
expose hashes for reuse in indexing.

This change is step 1 of 2:
(a) mv table/full_filter_bits_builder.h to
table/block_based/filter_policy_internal.h which I expect to expand
soon to internally reveal more implementation details for testing.
(b) consolidate eventual contents of table/block_based/filter_policy.cc
in util/bloom.cc, which has the most elaborate revision history
(see step 2 ...)

Step 2 soon to follow:
mv util/bloom.cc table/block_based/filter_policy.cc
This gets its own PR so that git has the best chance of following the
rename for blame purposes. Note that low-level shared implementation
details of Bloom filters are in util/bloom_impl.h.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5963

Test Plan: make check

Differential Revision: D18121199

Pulled By: pdillinger

fbshipit-source-id: 8f21732c3d8909777e3240e4ac3123d73140326a
2019-10-24 13:20:35 -07:00
Levi Tamasi
29ccf2075c Store the filter bits reader alongside the filter block contents (#5936)
Summary:
Amongst other things, PR https://github.com/facebook/rocksdb/issues/5504 refactored the filter block readers so that
only the filter block contents are stored in the block cache (as opposed to the
earlier design where the cache stored the filter block reader itself, leading to
potentially dangling pointers and concurrency bugs). However, this change
introduced a performance hit since with the new code, the metadata fields are
re-parsed upon every access. This patch reunites the block contents with the
filter bits reader to eliminate this overhead; since this is still a self-contained
pure data object, it is safe to store it in the cache. (Note: this is similar to how
the zstd digest is handled.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5936

Test Plan:
make asan_check

filter_bench results for the old code:

```
$ ./filter_bench -quick
WARNING: Assertions are enabled; benchmarks unnecessarily slow
Building...
Build avg ns/key: 26.7153
Number of filters: 16669
Total memory (MB): 200.009
Bits/key actual: 10.0647
----------------------------
Inside queries...
  Dry run (46b) ns/op: 33.4258
  Single filter ns/op: 42.5974
  Random filter ns/op: 217.861
----------------------------
Outside queries...
  Dry run (25d) ns/op: 32.4217
  Single filter ns/op: 50.9855
  Random filter ns/op: 219.167
    Average FP rate %: 1.13993
----------------------------
Done. (For more info, run with -legend or -help.)

$ ./filter_bench -quick -use_full_block_reader
WARNING: Assertions are enabled; benchmarks unnecessarily slow
Building...
Build avg ns/key: 26.5172
Number of filters: 16669
Total memory (MB): 200.009
Bits/key actual: 10.0647
----------------------------
Inside queries...
  Dry run (46b) ns/op: 32.3556
  Single filter ns/op: 83.2239
  Random filter ns/op: 370.676
----------------------------
Outside queries...
  Dry run (25d) ns/op: 32.2265
  Single filter ns/op: 93.5651
  Random filter ns/op: 408.393
    Average FP rate %: 1.13993
----------------------------
Done. (For more info, run with -legend or -help.)
```

With the new code:

```
$ ./filter_bench -quick
WARNING: Assertions are enabled; benchmarks unnecessarily slow
Building...
Build avg ns/key: 25.4285
Number of filters: 16669
Total memory (MB): 200.009
Bits/key actual: 10.0647
----------------------------
Inside queries...
  Dry run (46b) ns/op: 31.0594
  Single filter ns/op: 43.8974
  Random filter ns/op: 226.075
----------------------------
Outside queries...
  Dry run (25d) ns/op: 31.0295
  Single filter ns/op: 50.3824
  Random filter ns/op: 226.805
    Average FP rate %: 1.13993
----------------------------
Done. (For more info, run with -legend or -help.)

$ ./filter_bench -quick -use_full_block_reader
WARNING: Assertions are enabled; benchmarks unnecessarily slow
Building...
Build avg ns/key: 26.5308
Number of filters: 16669
Total memory (MB): 200.009
Bits/key actual: 10.0647
----------------------------
Inside queries...
  Dry run (46b) ns/op: 33.2968
  Single filter ns/op: 58.6163
  Random filter ns/op: 291.434
----------------------------
Outside queries...
  Dry run (25d) ns/op: 32.1839
  Single filter ns/op: 66.9039
  Random filter ns/op: 292.828
    Average FP rate %: 1.13993
----------------------------
Done. (For more info, run with -legend or -help.)
```

Differential Revision: D17991712

Pulled By: ltamasi

fbshipit-source-id: 7ea205550217bfaaa1d5158ebd658e5832e60f29
2019-10-18 19:32:59 -07:00
Peter Dillinger
46ca51d430 filter_bench - a prelim tool for SST filter benchmarking (#5825)
Summary:
Example: using the tool before and after PR https://github.com/facebook/rocksdb/issues/5784 shows that
the refactoring, presumed performance-neutral, actually sped up SST
filters by about 3% to 8% (repeatable result):

Before:
-  Dry run ns/op: 22.4725
-  Single filter ns/op: 51.1078
-  Random filter ns/op: 120.133

After:
+  Dry run ns/op: 22.2301
+  Single filter run ns/op: 47.4313
+  Random filter ns/op: 115.9

Only tests filters for the block-based table (full filters and
partitioned filters - same implementation; not block-based filters),
which seems to be the recommended format/implementation.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5825

Differential Revision: D17804987

Pulled By: pdillinger

fbshipit-source-id: 0f18a9c254c57f7866030d03e7fa4ba503bac3c5
2019-10-07 20:10:53 -07:00
sdong
b931f84e56 Divide file_reader_writer.h and .cc (#5803)
Summary:
file_reader_writer.h and .cc contain several files and helper function, and it's hard to navigate. Separate it to multiple files and put them under file/
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5803

Test Plan: Build whole project using make and cmake.

Differential Revision: D17374550

fbshipit-source-id: 10efca907721e7a78ed25bbf74dc5410dea05987
2019-09-16 10:33:51 -07:00
anand76
83a6a614e9 Refactor ArenaWrappedDBIter into separate files (#5801)
Summary:
Move definition and implementation for ArenaWrappedDBIter into its own .h/.cc files. Also, change inlining of functions to better comply with the Google C++ style guide.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5801

Test Plan: make check

Differential Revision: D17371012

Pulled By: anand1976

fbshipit-source-id: c1361abc2851575111e357a63d88be3b3d6cb341
2019-09-13 13:50:43 -07:00
Wilfried Goesgens
fcda80fc33 record the timestamp on first configure (#4799)
Summary:
cmake doesn't re-generate the timestamp on subsequent builds causing rebuilds of the lib

This improves compile time turn-arounds if you have rocksdb as a compileable library include, since with the state its now it will re-generate the time stamp .cc file each time you build, and thus re-compile + re-link the rocksdb library though anything in the source actually changed.
The original timestamp is recorded into `CMakeCache.txt` and will remain there until you flush this cache.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4799

Differential Revision: D17290040

fbshipit-source-id: 28357fef3422693c9c19e88fa2873c8db0f662ed
2019-09-11 18:00:02 -07:00
Wilfried Goesgens
fbab9913e2 upgrade gtest 1.7.0 => 1.8.1 for json result writing
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/5332

Differential Revision: D17242232

fbshipit-source-id: c0d4646556a1335e51ac7382b986ca7f6ced7b64
2019-09-09 11:24:11 -07:00
houbingjian
cbfa729d37 cmakelist fix, add +crypto flag when use arm crc (#5750)
Summary:
cmake list add +crypto flag when use armv8 cpu

the function crc32c_arm64 use HAVE_ARM64_CRYPTO to check if can enable arm-neon instructions :

#ifdef HAVE_ARM64_CRYPTO
  /* Crc32c Parallel computation
   *   Algorithm comes from Intel whitepaper:
   *   crc-iscsi-polynomial-crc32-instruction-paper
   *
   * Input data is divided into three equal-sized blocks
   *   Three parallel blocks (crc0, crc1, crc2) for 1024 Bytes
   *   One Block: 42(BLK_LENGTH) * 8(step length: crc32c_u64) bytes
   */

but the cmakelist not check and pass crypto flag now

I check the default Makefile has it:

ifeq (,$(shell $(CXX) -fsyntax-only -march=armv8-a+crc -xc /dev/null 2>&1))
CXXFLAGS += -march=armv8-a+crc+crypto
CFLAGS += -march=armv8-a+crc+crypto
ARMCRC_SOURCE=1
endif
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5750

Differential Revision: D17242027

fbshipit-source-id: 443c9b89755b4bc34e265205ab922db1b2e14bde
2019-09-06 17:03:21 -07:00
Peter Dillinger
20dec1401f Copy/split PlainTableBloomV1 from DynamicBloom (refactor) (#5767)
Summary:
DynamicBloom was being used both for memory-only and for on-disk filters, as part of the PlainTable format. To set up enhancements to the memtable Bloom filter, this splits the code into two copies and removes unused features from each copy. Adds test PlainTableDBTest.BloomSchema to ensure no accidental change to that format.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5767

Differential Revision: D17206963

Pulled By: pdillinger

fbshipit-source-id: 6cce8d55305ed0df051b4c58bdc98c8ad81d0553
2019-09-05 10:05:20 -07:00
Zhongyi Xie
2f41ecfe75 Refactor trimming logic for immutable memtables (#5022)
Summary:
MyRocks currently sets `max_write_buffer_number_to_maintain` in order to maintain enough history for transaction conflict checking. The effectiveness of this approach depends on the size of memtables. When memtables are small, it may not keep enough history; when memtables are large, this may consume too much memory.
We are proposing a new way to configure memtable list history: by limiting the memory usage of immutable memtables. The new option is `max_write_buffer_size_to_maintain` and it will take precedence over the old `max_write_buffer_number_to_maintain` if they are both set to non-zero values. The new option accounts for the total memory usage of flushed immutable memtables and mutable memtable. When the total usage exceeds the limit, RocksDB may start dropping immutable memtables (which is also called trimming history), starting from the oldest one.
The semantics of the old option actually works both as an upper bound and lower bound. History trimming will start if number of immutable memtables exceeds the limit, but it will never go below (limit-1) due to history trimming.
In order the mimic the behavior with the new option, history trimming will stop if dropping the next immutable memtable causes the total memory usage go below the size limit. For example, assuming the size limit is set to 64MB, and there are 3 immutable memtables with sizes of 20, 30, 30. Although the total memory usage is 80MB > 64MB, dropping the oldest memtable will reduce the memory usage to 60MB < 64MB, so in this case no memtable will be dropped.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5022

Differential Revision: D14394062

Pulled By: miasantreble

fbshipit-source-id: 60457a509c6af89d0993f988c9b5c2aa9e45f5c5
2019-08-23 13:55:34 -07:00
Aaryaman Sagar
38b03c840e Port folly/synchronization/DistributedMutex to rocksdb (#5642)
Summary:
This ports `folly::DistributedMutex` into RocksDB. The PR includes everything else needed to compile and use DistributedMutex as a component within folly. Most files are unchanged except for some portability stuff and includes.

For now, I've put this under `rocksdb/third-party`, but if there is a better folder to put this under, let me know. I also am not sure how or where to put unit tests for third-party stuff like this. It seems like gtest is included already, but I need to link with it from another third-party folder.

This also includes some other common components from folly

- folly/Optional
- folly/ScopeGuard (In particular `SCOPE_EXIT`)
- folly/synchronization/ParkingLot (A portable futex-like interface)
- folly/synchronization/AtomicNotification (The standard C++ interface for futexes)
- folly/Indestructible (For singletons that don't get destroyed without allocations)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5642

Differential Revision: D16544439

fbshipit-source-id: 179b98b5dcddc3075926d31a30f92fd064245731
2019-08-07 14:34:19 -07:00
Vijay Nadimpalli
d150e01474 New API to get all merge operands for a Key (#5604)
Summary:
This is a new API added to db.h to allow for fetching all merge operands associated with a Key. The main motivation for this API is to support use cases where doing a full online merge is not necessary as it is performance sensitive. Example use-cases:
1. Update subset of columns and read subset of columns -
Imagine a SQL Table, a row is encoded as a K/V pair (as it is done in MyRocks). If there are many columns and users only updated one of them, we can use merge operator to reduce write amplification. While users only read one or two columns in the read query, this feature can avoid a full merging of the whole row, and save some CPU.
2. Updating very few attributes in a value which is a JSON-like document -
Updating one attribute can be done efficiently using merge operator, while reading back one attribute can be done more efficiently if we don't need to do a full merge.
----------------------------------------------------------------------------------------------------
API :
Status GetMergeOperands(
      const ReadOptions& options, ColumnFamilyHandle* column_family,
      const Slice& key, PinnableSlice* merge_operands,
      GetMergeOperandsOptions* get_merge_operands_options,
      int* number_of_operands)

Example usage :
int size = 100;
int number_of_operands = 0;
std::vector<PinnableSlice> values(size);
GetMergeOperandsOptions merge_operands_info;
db_->GetMergeOperands(ReadOptions(), db_->DefaultColumnFamily(), "k1", values.data(), merge_operands_info, &number_of_operands);

Description :
Returns all the merge operands corresponding to the key. If the number of merge operands in DB is greater than merge_operands_options.expected_max_number_of_operands no merge operands are returned and status is Incomplete. Merge operands returned are in the order of insertion.
merge_operands-> Points to an array of at-least merge_operands_options.expected_max_number_of_operands and the caller is responsible for allocating it. If the status returned is Incomplete then number_of_operands will contain the total number of merge operands found in DB for key.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5604

Test Plan:
Added unit test and perf test in db_bench that can be run using the command:
./db_bench -benchmarks=getmergeoperands --merge_operator=sortlist

Differential Revision: D16657366

Pulled By: vjnadimpalli

fbshipit-source-id: 0faadd752351745224ee12d4ae9ef3cb529951bf
2019-08-06 14:26:44 -07:00