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

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

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

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

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

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

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

Summary:
Revert "Use function objects as deleters in the block cache (https://github.com/facebook/rocksdb/issues/6545)"

    This reverts commit 6301dbe7.

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

    This reverts commit 3a35542f.
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

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

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

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

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

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

Summary:
Preliminary support for iterator with user timestamp. Current implementation does not consider merge operator and reverse iterator. Auto compaction is also disabled in unit tests.

Create an iterator with timestamp.
```
...
read_opts.timestamp = &ts;
auto* iter = db->NewIterator(read_opts);
// target is key without timestamp.
for (iter->Seek(target); iter->Valid(); iter->Next()) {}
for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {}
delete iter;
read_opts.timestamp = &ts1;
// lower_bound and upper_bound are without timestamp.
read_opts.iterate_lower_bound = &lower_bound;
read_opts.iterate_upper_bound = &upper_bound;
auto* iter1 = db->NewIterator(read_opts);
// Do Seek or SeekToFirst()
delete iter1;
```

Test plan (dev server)
```
$make check
```

Simple benchmarking (dev server)
1. The overhead introduced by this PR even when timestamp is disabled.
key size: 16 bytes
value size: 100 bytes
Entries: 1000000
Data reside in main memory, and try to stress iterator.
Repeated three times on master and this PR.
- Seek without next
```
./db_bench -db=/dev/shm/rocksdbtest-1000 -benchmarks=fillseq,seekrandom -enable_pipelined_write=false -disable_wal=true -format_version=3
```
master: 159047.0 ops/sec
this PR: 158922.3 ops/sec (2% drop in throughput)
- Seek and next 10 times
```
./db_bench -db=/dev/shm/rocksdbtest-1000 -benchmarks=fillseq,seekrandom -enable_pipelined_write=false -disable_wal=true -format_version=3 -seek_nexts=10
```
master: 109539.3 ops/sec
this PR: 107519.7 ops/sec (2% drop in throughput)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6255

Differential Revision: D19438227

Pulled By: riversand963

fbshipit-source-id: b66b4979486f8474619f4aa6bdd88598870b0746

Summary:
Original author: jeffrey-xiao

If we are writing a global seqno for an ingested file, the range
tombstone metablock gets accessed and put into the cache during
ingestion preparation. At the time, the global seqno of the ingested
file has not yet been determined, so the cached block will not have a
global seqno. When the file is ingested and we read its range tombstone
metablock, it will be returned from the cache with no global seqno. In
that case, we use the actual seqnos stored in the range tombstones,
which are all zero, so the tombstones cover nothing.

This commit removes global_seqno_ variable from Block. When iterating
over a block, the global seqno for the block is determined by the
iterator instead of storing this mutable attribute in Block.
Additionally, this commit adds a regression test to check that keys are
deleted when ingesting a file with a global seqno and range deletion
tombstones.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6429

Differential Revision: D19961563

Pulled By: ajkr

fbshipit-source-id: 5cf777397fa3e452401f0bf0364b0750492487b7

Summary:
Cleanup some code without any real change in functionality.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6440

Differential Revision: D20015891

Pulled By: riversand963

fbshipit-source-id: 33e18754b0f002006a6d4805e9aaf84c0c8ad25a

Summary:
When dynamically linking two binaries together, different builds of RocksDB from two sources might cause errors. To provide a tool for user to solve the problem, the RocksDB namespace is changed to a flag which can be overridden in build time.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6433

Test Plan: Build release, all and jtest. Try to build with ROCKSDB_NAMESPACE with another flag.

Differential Revision: D19977691

fbshipit-source-id: aa7f2d0972e1c31d75339ac48478f34f6cfcfb3e

Summary:
Unrevert the previous fix to propagate error status, and an additional fix to not treat a memtable lookup MergeInProgress status as an error.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6403

Test Plan:
Unit tests
Tried running stress tests but couldn't repro the stress failure

Differential Revision: D19846721

Pulled By: anand1976

fbshipit-source-id: 7db10cccbdc863d9b559497f0a46b608d2488ca4

Summary:
This reverts commit d70011bc. The commit is causing some stress test failure due to unexpected Status::MergeInProgress() return for some keys.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6401

Differential Revision: D19826623

Pulled By: anand1976

fbshipit-source-id: edd634cede9cb7bdd2cb8f46e662ea709b16d2f1

Summary:
Currently, any IO errors and checksum mismatches while reading data
blocks, are being ignored by the batched MultiGet. Its only looking at
the GetContext state. Fix that.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6387

Test Plan: Add unit tests

Differential Revision: D19799819

Pulled By: anand1976

fbshipit-source-id: 46133dccbb04e64067b9fe6cda73e282203db969

Summary:
Add a new option ReadOptions.auto_prefix_mode. When set to true, iterator should return the same result as total order seek, but may choose to do prefix seek internally, based on iterator upper bounds. Also fix two previous bugs when handling prefix extrator changes: (1) reverse iterator should not rely on upper bound to determine prefix. Fix it with skipping prefix check. (2) block-based filter is not handled properly.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6314

Test Plan: (1) add a unit test; (2) add the check to stress test and run see whether it can pass at least one run.

Differential Revision: D19458717

fbshipit-source-id: 51c1bcc5cdd826c2469af201979a39600e779bce

Summary:
https://github.com/facebook/rocksdb/pull/6028 introduces a bug for hash index in SST files. If a table reader is created when total order seek is used, prefix_extractor might be passed into table reader as null. While later when prefix seek is used, the same table reader used, hash index is checked but prefix extractor is null and the program would crash.
Fix the issue by fixing http://github.com/facebook/rocksdb/pull/6028 in the way that prefix_extractor is preserved but ReadOptions.total_order_seek is checked

Also, a null pointer check is added so that a bug like this won't cause segfault in the future.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6328

Test Plan: Add a unit test that would fail without the fix. Stress test that reproduces the crash would pass.

Differential Revision: D19586751

fbshipit-source-id: 8de77690167ddf5a77a01e167cf89430b1bfba42

Summary:
Recent bug fix related to hash index introduced a new bug: hash index can return NotFound but it is not handled by BlockBasedTable::Get(). The end result is that Get() stops being executed too early. Fix it by ignoring NotFound code in Get().
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6305

Test Plan: A problematic DB used to return NotFound incorrectly, and now able to return correct result. Will try to construct a unit test too.0

Differential Revision: D19438925

fbshipit-source-id: e751afa8c13728d56511cfeb1bc811ecb99f3217

Summary:
When prefix is enabled the expected behavior when the prefix of the target does not exist is for Seek is to seek to any key larger than target and SeekToPrev to any key less than the target.
Currently. the prefix index (kHashSearch) returns OK status but sets Invalid() to indicate two cases: a prefix of the searched key does not exist, ii) the key is beyond the range of the keys in SST file. The SeekForPrev implementation in BlockBasedTable thus does not have enough information to know when it should set the index key to first (to return a key smaller than target). The patch fixes that by returning NotFound status for cases that the prefix does not exist. SeekForPrev in BlockBasedTable accordingly SeekToFirst instead of SeekToLast on the index iterator.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6297

Test Plan: SeekForPrev of non-exsiting prefix is added to block_test.cc, and a test case is added in db_test2, which fails without the fix.

Differential Revision: D19404695

fbshipit-source-id: cafbbf95f8f60ff9ede9ccc99d25bfa1cf6fcdc3

Summary:
Right now BlockBasedTable::ApproximateSize() uses default setting about whether to use total order seek. There is no reason for that. There is no reason to do any filtering for approximate size boundary key, and it may introduce bugs. Disable it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6222

Test Plan: Run existing tests

Differential Revision: D19184787

fbshipit-source-id: 64180660bd2800914fff75104172b61c06f0b1c9

Summary:
Right now, sometimes file prefetching is still on when mmap is enabled. This causes bug of reading wrong data. In this commit, we remove all those possible paths.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6206

Test Plan: make crash_test with compaction_readahead_size, which used to fail. RUn all existing tests.

Differential Revision: D19149429

fbshipit-source-id: 9e18ea8c566e416aac9647bdd05afe596634791b

Summary:
buf_offset does not need to get the value from req.len for othe final block. It can cause test fail for clan_analyze. Remove it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6204

Test Plan: pass make asan_check

Differential Revision: D19145335

Pulled By: zhichao-cao

fbshipit-source-id: 8f6e74565746381b5c5ef598b97d746517b36e5b

Summary:
In the current MultiGet, if the KV-pairs do not belong to the data blocks in the block cache, multiple blocks are read from a SST. It will trigger one block read for each block request and read them in parallel. In some cases, if some data blocks are adjacent in the SST, the reads for these blocks can be combined to a single large read, which can reduce the system calls and reduce the read latency if possible.

Considering to fill the block cache, if multiple data blocks are in the same memory buffer, we need to copy them to the heap separately. Therefore, only in the case that 1) data block compression is enabled, and 2) compressed block cache is null, we can do combined read. Otherwise, extra memory copy is needed, which may cause extra overhead. In the current case, data blocks will be uncompressed to a new memory space.

Also, in the case that 1) data block compression is enabled, and 2) compressed block cache is null, it is possible the data block is actually not compressed. In the current logic, these data blocks will not be added to the uncompressed_cache. So if memory buffer is shared and the data block is not compressed, the data block are copied to the head and fill the cache.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6089

Test Plan: Added test case to ParallelIO.MultiGet. Pass make asan_check

Differential Revision: D18734668

Pulled By: zhichao-cao

fbshipit-source-id: 67c5615ed373e51e42635fd74b36f8f3a66d5da4

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

Summary:
The calculation in BlockBasedTable::MultiGet for the required buffer length for reading in compressed blocks is incorrect. It needs to take the 5-byte block trailer into account.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6014

Test Plan: Add a unit test DBBasicTest.MultiGetBufferOverrun that fails in asan_check before the fix, and passes after.

Differential Revision: D18412753

Pulled By: anand1976

fbshipit-source-id: 754dfb66be1d5f161a7efdf87be872198c7e3b72

Summary:
This PR fixes https://github.com/facebook/rocksdb/issues/5975. In ```BlockBasedTable::RetrieveMultipleBlocks()```, we were calling ```MaybeReadBlocksAndLoadToCache()```, which is a no-op if neither uncompressed nor compressed block cache are configured.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5991

Test Plan:
1. Add unit tests that fail with the old code and pass with the new
2. make check and asan_check

Cc spetrunia

Differential Revision: D18272744

Pulled By: anand1976

fbshipit-source-id: e62fa6090d1a6adf84fcd51dfd6859b03c6aebfe

Summary:
According to
https://github.com/facebook/rocksdb/wiki/Rocksdb-BlockBasedTable-Format,
the block read by BlockBasedTable::ReadMetaBlock is actually the meta index
block. Therefore, it is better to rename the function to ReadMetaIndexBlock.

This PR also applies some format change to existing code.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6009

Test Plan: make check

Differential Revision: D18333238

Pulled By: riversand963

fbshipit-source-id: 2c4340a29b3edba53d19c132cbfd04caf6242aed

Summary:
A recent change introduced readahead inside VerifyChecksum(). However it is not compatible with mmap mode and generated wrong checksum verification failure. Fix it by not enabling readahead in mmap
 mode.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5945

Test Plan: Add a unit test that used to fail.

Differential Revision: D18021443

fbshipit-source-id: 6f2eb600f81b26edb02222563a4006869d576bff

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

Summary:
Since we do not evict a file's blocks from block cache before that file
is deleted, we require a file's cache ID prefix is both unique and
non-reusable. However, the Windows functionality we were relying on only
guaranteed uniqueness. That meant a newly created file could be assigned
the same cache ID prefix as a deleted file. If the newly created file
had block offsets matching the deleted file, full cache keys could be
exactly the same, resulting in obsolete data blocks returned from cache
when trying to read from the new file.

We noticed this when running on FAT32 where compaction was writing out
of order keys due to reading obsolete blocks from its input files. The
functionality is documented as behaving the same on NTFS, although I
wasn't able to repro it there.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5844

Test Plan:
we had a reliable repro of out-of-order keys on FAT32 that
was fixed by this change

Differential Revision: D17752442

fbshipit-source-id: 95d983f9196cf415f269e19293b97341edbf7e00

Summary:
When an iterator reseek happens with the user specifying a new iterate_upper_bound in ReadOptions, and the new seek position is at the end of the same data block, the Seek() ends up using a stale value of data_block_within_upper_bound_ and may return incorrect results.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5883

Test Plan: Added a new test case DBIteratorTest.IterReseekNewUpperBound. Verified that it failed due to the assertion failure without the fix, and passes with the fix.

Differential Revision: D17752740

Pulled By: anand1976

fbshipit-source-id: f9b635ff5d6aeb0e1bef102cf8b2f900efd378e3

Summary:
Further apply formatter to more recent commits.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5830

Test Plan: Run all existing tests.

Differential Revision: D17488031

fbshipit-source-id: 137458fd94d56dd271b8b40c522b03036943a2ab

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

Summary:
PR https://github.com/facebook/rocksdb/issues/5584 decoupled the uncompression dictionary object from the underlying block data; however, this defeats the purpose of the digested ZSTD dictionary, since the whole point
of the digest is to create it once and reuse it over and over again. This patch goes back to
storing the uncompression dictionary itself in the cache (which should be now safe to do,
since it no longer includes a Statistics pointer), while preserving the rest of the refactoring.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5645

Test Plan: make asan_check

Differential Revision: D16551864

Pulled By: ltamasi

fbshipit-source-id: 2a7e2d34bb16e70e3c816506d5afe1d842057800

Summary:
To improve code readability, since RetrieveBlock already calls MaybeReadBlockAndLoadToCache, we avoid name similarity of the functions that call RetrieveBlock with MaybeReadBlockAndLoadToCache. The patch thus renames MaybeLoadBlocksToCache to RetrieveMultipleBlock and deletes GetDataBlockFromCache, which contains only two lines.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5726

Differential Revision: D16962535

Pulled By: maysamyabandeh

fbshipit-source-id: 99e8946808ce4eb7857592b9003812e3004f92d6