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
Summary:
We found some files containing nothing but negative range tombstones,
and unsurprisingly their metadata specified a negative range, which made
things crash. Time to add a bit of user input validation.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6788
Reviewed By: zhichao-cao
Differential Revision: D21343719
Pulled By: ajkr
fbshipit-source-id: f1c16e4c3e9fa150958c8c866176632a3206fb74
Summary:
The patch extends `FindObsoleteFiles` and `PurgeObsoleteFiles` with
support for blob files. The behavior is analogous to SST files: obsolete
blob files are put on the "candidates for deletion" list, while live (and pending)
files are preserved.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6807
Test Plan: `make check`
Reviewed By: riversand963
Differential Revision: D21406249
Pulled By: ltamasi
fbshipit-source-id: 1948f71c31927564b61e8af394f50ca3964880d9
Summary:
https://github.com/facebook/rocksdb/pull/6807 extends the logic that
identifies and purges obsolete files to blob files handled by RocksDB
itself. In order to prevent that from interfering with the current BlobDB code,
we need to make sure that `BlobDBOptions::blob_dir` is different from
the storage directories used by the base DB. (Note: this is true by default.)
The patch adds a check that explicitly disallows this configuration and
returns `Status::NotSupported` from `BlobDB::Open` in such cases.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6810
Test Plan: Tested using the BlobDB mode of `db_bench`.
Reviewed By: riversand963
Differential Revision: D21412676
Pulled By: ltamasi
fbshipit-source-id: 6630cc7481e48c8bf55d59423b25f14d52ffe681
Summary:
Current DBCompactionTest.ConsistencyFailTest checks DB fails after L0 inconsitency is found. Add slightly more coverage by introducing DBCompactionTest.ConsistencyFailTest2 which checks non-L0 files too.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6800
Test Plan: Run the new test.
Reviewed By: riversand963
Differential Revision: D21384806
fbshipit-source-id: 36db7b657eed42115283fe2f6afa4c3a31a3b510
Summary:
Add methods and constructors for handling enums to the OptionTypeInfo. This change allows enums to be converted/compared without adding a special "type" to the OptionType.
This change addresses a couple of issues:
- It allows new enumerated types to be added to the options without editing the OptionType base class (and related methods)
- It standardizes the procedure for adding enumerated types to the options, reducing potential mistakes
- It moves the enum maps to the location where they are used, allowing them to be static file members rather than global values
- It reduces the number of types and cases that need to be handled in the various OptionType methods
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6423
Reviewed By: siying
Differential Revision: D21408713
Pulled By: zhichao-cao
fbshipit-source-id: fc492af285d011822578b95d186a0fce25d35626
Summary:
This very old test code bug was causing a new valgrind failure
in MultiGetDeadlineExceeded
Also fix hang in MultiGetDeadlineExceeded by unifying with some logic from another test.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6803
Test Plan: run that unit test under valgrind, make check
Reviewed By: siying
Differential Revision: D21388470
Pulled By: pdillinger
fbshipit-source-id: 0ce99d6d5eb8cd3195b17406892c8c5cff5fa5dd
Summary:
With consistency check enabled, VersionBuilder::SaveTo() may return error once
corruption is detected while building versions. We should handle these errors.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6801
Test Plan: make check
Reviewed By: siying
Differential Revision: D21385045
Pulled By: riversand963
fbshipit-source-id: 98f6424e2a4699b62befa21e9fe00e70a771118e
Summary:
Current impl. of db_stress will abort verification and report failure if
GetLiveFiles() causes a dropped column family to be flushed. This is not
desired.
To fix, this PR makes the following change:
In GetLiveFiles, if flush is triggered and returns
Status::IsColumnFamilyDropped(), then set status to Status::OK().
This is OK because dropped column families will be skipped during the rest of
this function, and valid column families will have their live files returned to
caller.
Test plan (dev server):
make check
./db_stress -ops_per_thread=1000 -get_live_files_one_in=100 -clear_column_family_one_in=100
./db_stress -disable_wal=1 -reopen=0 -ops_per_thread=1000 -get_live_files_one_in=100 -clear_column_family_one_in=100
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6805
Reviewed By: ltamasi
Differential Revision: D21390044
Pulled By: riversand963
fbshipit-source-id: de67846b95a4f1b88aa0a30c3d70c43cc68625b9
Summary:
The patch adds logic that returns the set of live blob files from
`Version::AddLiveFiles` and `VersionSet::AddLiveFiles` (in addition to
live table files), and also cleans up the code a bit, for example, by
exposing only the numbers of table files as opposed to the earlier
`FileDescriptor`s that no clients used. Moreover, the patch extends
the `GetLiveFiles` API so that it also exposes blob files in the current version.
Similarly to https://github.com/facebook/rocksdb/pull/6755,
this is a building block for identifying and purging obsolete blob files.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6785
Test Plan: `make check`
Reviewed By: riversand963
Differential Revision: D21336210
Pulled By: ltamasi
fbshipit-source-id: fc1aede8a49eacd03caafbc5f6f9ce43b6270821
Summary:
We are swallowing some file consistency checking failures. This is not expected. We are fixing two cases: DB reopen and manifest dump.
More places are not fixed and need follow-up.
Error from CheckConsistencyForDeletes() is also swallowed, which is not fixed in this PR.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6793
Test Plan: Add a unit test to cover the reopen case.
Reviewed By: riversand963
Differential Revision: D21366525
fbshipit-source-id: eb438a322237814e8d5125f916a3c6de97f39ded
Summary:
Fix issues for reproducing synthetic ZippyDB workloads in the FAST20' paper using db_bench. Details changes as follows.
1, add a separate random mode in MixGraph to produce all_random workload.
2, fix power inverse function for generating prefix_dist workload.
3, make sure key_offset in prefix mode is always unsigned.
note: Need to carefully choose key_dist_a/b to avoid aliasing. Power inverse function range should be close to overall key space.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6795
Reviewed By: akankshamahajan15
Differential Revision: D21371095
Pulled By: zhichao-cao
fbshipit-source-id: 80744381e242392c8c7cf8ac3d68fe67fe876048
Summary:
When expiration is set in a pessimistic transaction, `txn_state_` is already updated to `AWAITING_PREPARE` in the `if (expiration_time_ > 0)` block, there is no need to update the state in `if (can_prepare)` block again.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6778
Test Plan: make check
Reviewed By: lth
Differential Revision: D21335319
Pulled By: cheng-chang
fbshipit-source-id: 251d634cc7d1a0e86e673a59f0bda8584da5a35f
Summary:
The multiple CF hash map is not passed to the multi-thread worker. When using multi-thread replay for multiple CFs, it will cause segment fault. Pass the cf_map to the argument.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6787
Test Plan: pass trace replay test.
Reviewed By: yhchiang
Differential Revision: D21339941
Pulled By: zhichao-cao
fbshipit-source-id: 434482b492287e6722c7cd5a706f057c5ec170ce
Summary:
Add Github Action to perform some basic sanity check for PR, inclding the
following.
1) Buck TARGETS file.
On the one hand, The TARGETS file is used for internal buck, and we do not
manually update it. On the other hand, we need to run the buckifier scripts to
update TARGETS whenever new files are added, etc. With this Github Action, we
make sure that every PR does not forget this step. The GH Action uses
a Makefile target called check-buck-targets. Users can manually run `make
check-buck-targets` on local machine.
2) Code format
We use clang-format-diff.py to format our code. The GH Action in this PR makes
sure this step is not skipped. The checking script build_tools/format-diff.sh assumes that `clang-format-diff.py` is executable.
On host running GH Action, it is difficult to download `clang-format-diff.py` and make it
executable. Therefore, we modified build_tools/format-diff.sh to handle the case in which there is a non-executable clang-format-diff.py file in the top-level rocksdb repo directory.
Test Plan (Github and devserver):
Watch for Github Action result in the `Checks` tab.
On dev server
```
make check-format
make check-buck-targets
make check
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6761
Test Plan: Watch for Github Action result in the `Checks` tab.
Reviewed By: pdillinger
Differential Revision: D21260209
Pulled By: riversand963
fbshipit-source-id: c646e2f37c6faf9f0614b68aa0efc818cff96787
Summary:
The current way of implementing CompressionOptions.parallel_threads introduces a format change. We plan to change CompressionOptions's serailization format to a new JSON-like format, which would be another format change. We would like to consolidate the two format changes into one, rather than making some users to change twice. Hold CompressionOptions.parallel_threads from being supported by option string for now. Will add it back after the general CompressionOptions's format change.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6782
Test Plan: Run all existing tests.
Reviewed By: zhichao-cao
Differential Revision: D21338614
fbshipit-source-id: bca2dac3cb37d4e6e64b52cbbe8ea749cd848685
Summary:
In current commit protocol of pessimistic transaction, if the transaction is not prepared before commit, the commit protocol implicitly assumes that the user wants to commit without prepare.
This PR adds TransactionOptions::skip_prepare, the default value is `true` because if set to `false`, all existing users who commit without prepare need to update their code to set skip_prepare to true. Although this does not force the user to explicitly express their intention of skip_prepare, it at least lets the user be aware of the assumption of being able to commit without prepare.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6775
Test Plan: added a new unit test TransactionTest::CommitWithoutPrepare
Reviewed By: lth
Differential Revision: D21313270
Pulled By: cheng-chang
fbshipit-source-id: 3d95b7c9b2d6cdddc09bdd66c561bc4fae8c3251
Summary:
There is no systematic mechanism to prevent BlockBasedTableBuilder's status to be set from non-OK to OK. Adding a mechanism to force this will help us prevent failures in the future.
The solution is to only make it possible to set the status code if the status code to set is not OK.
Since the status code passed to CompressAndVerifyBlock() is changed, a mini refactoring is done too so that the output arguments are changed from reference to pointers, based on Google C++ Style.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6776
Test Plan: Run all existing test.
Reviewed By: pdillinger
Differential Revision: D21314382
fbshipit-source-id: 27000c10f1e4c121661e026548d6882066409375
Summary:
The feature of CompressionOptions::parallel_threads is still not yet mature. Mention it to be experimental in the comments for now.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6781
Reviewed By: pdillinger
Differential Revision: D21330678
fbshipit-source-id: d7dd7d099fb002a5c6a5d8da689ce5ee08a9eb13
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
Summary:
An assertion that a char == a CompressionType (unsigned char)
originally cast from a char can fail if the original value is negative,
due to numeric promotion. The assertion should pass even if the value
is invalid CompressionType, because the callee
UncompressBlockContentsForCompressionType checks for that and reports
status appropriately.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6780
Test Plan:
Temporarily change kZSTD = 0x88 and see tests fail. Make this
change (in addition), and tests pass.
Reviewed By: siying
Differential Revision: D21328498
Pulled By: pdillinger
fbshipit-source-id: 61caf8d815581ce49261ecb7ab0f396e9ac4bb92
Summary:
The patch adds logic to keep track of obsolete blob files. A blob file becomes
obsolete when the last `shared_ptr` that points to the corresponding
`SharedBlobFileMetaData` object goes away, which, in turn, happens when the
last `Version` that contains the blob file is destroyed. No longer needed blob
files are added to the obsolete list in `VersionSet` using a custom deleter to
avoid unnecessary coupling between `SharedBlobFileMetaData` and `VersionSet`.
Obsolete blob files are returned by `VersionSet::GetObsoleteFiles` and stored
in `JobContext`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6755
Test Plan: `make check`
Reviewed By: riversand963
Differential Revision: D21233155
Pulled By: ltamasi
fbshipit-source-id: 47757e06fdc0127f27ed57f51abd27893d9a7b7a
Summary:
This commit adds an `compression_parallel_threads` option in
db_stress. It also fixes the naming of parallel compression
option in db_bench to keep it aligned with others.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6722
Reviewed By: pdillinger
Differential Revision: D21091385
fbshipit-source-id: c9ba8c4e5cc327ff9e6094a6dc6a15fcff70f100
Summary:
The issue is reported in https://github.com/facebook/rocksdb/issues/6753 . size_t is unsigned and if sorted_file.size() is 0, the end condition of i will be extremely large, cause segment fault in sorted_files[i] and sorted_files[i+1]. Added condition to fix it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6762
Test Plan: make asan_check
Reviewed By: pdillinger
Differential Revision: D21323063
Pulled By: zhichao-cao
fbshipit-source-id: 56ce59201949ed319448228553202b8642c2cc3a
Summary:
Fix the following cases that can cause false alarms in db_stress when read fault injection is
enabled -
1. Turn off corruption/truncation when direct IO is enabled. Since the actual IO size is larger than block size due to alignment requirements, the corruption may not result in a detectable error.
2. Handle the case when the randomly generated string to overwrite the original block is identical to the original.
Tests:
Run db_stress w/ and wo/ direct IO and fault injection turned on
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6777
Reviewed By: zhichao-cao
Differential Revision: D21316734
Pulled By: anand1976
fbshipit-source-id: bf0e6468043063ca81ff877d4bf71d3f296c77aa
Summary:
Nasty bug in which more/different changes would be applied than
those shown to user
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6772
Test Plan: manual
Reviewed By: siying
Differential Revision: D21304604
Pulled By: pdillinger
fbshipit-source-id: 7e20740e513c9c300d1522511290a025b35abedc
Summary:
The dynamic_cast in the filter benchmark causes release mode to fail due to
no-rtti. Replace with static_cast_with_check.
Signed-off-by: Derrick Pallas <derrick@pallas.us>
Addition by peterd: Remove unnecessary 2nd template arg on all static_cast_with_check
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6732
Reviewed By: ltamasi
Differential Revision: D21304260
Pulled By: pdillinger
fbshipit-source-id: 6e8eb437c4ca5a16dbbfa4053d67c4ad55f1608c
Summary:
Added functions for parsing, serializing, and comparing elements to OptionTypeInfo. These functions allow all of the special cases that could not be handled directly in the map of OptionTypeInfo to be moved into the map. Using these functions, every type can be handled via the map rather than special cased.
By adding these functions, the code for handling options can become more standardized (fewer special cases) and (eventually) handled completely by common classes.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6422
Test Plan: pass make check
Reviewed By: siying
Differential Revision: D21269005
Pulled By: zhichao-cao
fbshipit-source-id: 9ba71c721a38ebf9ee88259d60bd81b3282b9077
Summary:
GetSupportedCompressions needs to be defined under LITE.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6758
Test Plan: build under LITE
Reviewed By: zhichao-cao
Differential Revision: D21247937
Pulled By: cheng-chang
fbshipit-source-id: 880e59d3e107cdd736d16427a68c5641d1318fb4
Summary:
If an error happens during BlobDBImpl::Open after the base DB has been
opened, we need to destroy the `ColumnFamilyHandle`s returned by `DB::Open`
to prevent an assertion in `ColumnFamilySet`'s destructor from being hit.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6763
Test Plan: Ran `make check` and tested using the BlobDB mode of `db_bench`.
Reviewed By: riversand963
Differential Revision: D21262643
Pulled By: ltamasi
fbshipit-source-id: 60ebc7ab19be66cf37fbe5f6d8957d58470f3d3b
Summary:
Fixed minor typo in comment for FullMergeV2().
Last operand up to snapshot should be +4 instead of +3.
Signed-off-by: Albert Hse-Lin Chen <hselin@kalista.io>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6759
Reviewed By: cheng-chang
Differential Revision: D21260295
Pulled By: zhichao-cao
fbshipit-source-id: cc942306f246c8606538feb30bfdf6df9fb6c54e
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:
Summary : 1. Add two arguments --compression_level_from and --compression_level_to to check
the compression size with different compression level in the given range. Users must
specify one compression type else it will error out. Both from and to levels must
also be specified together.
2. Display the time taken to compress each file with different compressions by default.
Test Plan : make -j64 check
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6634
Test Plan: make -j64 check
Reviewed By: anand1976
Differential Revision: D20810282
Pulled By: akankshamahajan15
fbshipit-source-id: ac9098d3c079a1fad098f6678dbedb4d888a791b
Summary:
Some common build variables like USE_CLANG and
COMPILE_WITH_UBSAN did not work if specified as make variables, as in
`make USE_CLANG=1 check` etc. rather than (in theory less hygienic)
`USE_CLANG=1 make check`. This patches Makefile to export some commonly
used ones to build_detect_platform so that they work. (I'm skeptical of
a broad `export` in Makefile because it's hard to predict how random
make variables might affect various invoked tools.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6740
Test Plan: manual / CI
Reviewed By: siying
Differential Revision: D21229011
Pulled By: pdillinger
fbshipit-source-id: b00c69b23eb2a13105bc8d860ce2d1e61ac5a355
Summary:
Some recent PRs added new source files or modified TARGETS file manually.
During next internal release, executing the following command will revert the
manual changes.
Update buckifier so that the following command
```
python buckfier/buckify_rocksdb.py
```
does not change TARGETS file.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6726
Test Plan:
```
python buckifier/buckify_rocksdb.py
```
Reviewed By: siying
Differential Revision: D21098930
Pulled By: riversand963
fbshipit-source-id: e884f507fefef88163363c9097a460c98f1ed850
Summary:
In crash test, the db directory might be set to /dev/shm or /tmp, in certain environments such as internal testing infrastructure, neither of these directories support direct IO, so direct IO is never enabled in crash test.
This PR sets up SyncPoints in direct IO related code paths to disable O_DIRECT flag in calls to `open`, so the direct IO code paths will be executed, all direct IO related assertions will be checked, but no real direct IO request will be issued to the file system.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6727
Test Plan:
export CRASH_TEST_EXT_ARGS="--use_direct_reads=1 --mmap_read=0"
make -j24 crash_test
Reviewed By: zhichao-cao
Differential Revision: D21139250
Pulled By: cheng-chang
fbshipit-source-id: db9adfe78d91aa4759835b1af91c5db7b27b62ee
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
Peter Dillinger