Summary:
There's a group of stats in PerfContext for profiling the write path. They break down the write time into WAL write, memtable insert, throttling, and everything else. We use these stats a lot for figuring out the cause of slow writes.
These stats got a bit out of date and are now categorizing some interesting things as "everything else", and also do some double counting. This PR fixes it and adds two new stats: time spent waiting for other threads of the batch group, and time spent waiting for scheduling flushes/compactions. Probably these will be enough to explain all the occasional abnormally slow (multiple seconds) writes that we're seeing.
Closes https://github.com/facebook/rocksdb/pull/3602
Differential Revision: D7251562
Pulled By: al13n321
fbshipit-source-id: 0a2d0f5a4fa5677455e1f566da931cb46efe2a0d
Summary:
This reverts commit 73f21a7b21.
It breaks compatibility. When created a DB using a build with this new change, opening the DB and reading the data will fail with this error:
"Corruption: Can't access /000000.sst: IO error: while stat a file for size: /tmp/xxxx/000000.sst: No such file or directory"
This is because the dummy AddFile4 entry generated by the new code will be treated as a real entry by an older build. The older build will think there is a real file with number 0, but there isn't such a file.
Closes https://github.com/facebook/rocksdb/pull/3762
Differential Revision: D7730035
Pulled By: siying
fbshipit-source-id: f2051859eff20ef1837575ecb1e1bb96b3751e77
Summary:
1. Add a new ticker stat rocksdb.number.multiget.keys.found to track the
number of keys successfully read
2. Update rocksdb.memtable.hit/miss in DBImpl::MultiGet(). It was being done in
DBImpl::GetImpl(), but not MultiGet
Closes https://github.com/facebook/rocksdb/pull/3730
Differential Revision: D7677364
Pulled By: anand1976
fbshipit-source-id: af22bd0ef8ddc5cf2b4244b0a024e539fe48bca5
Summary:
The WriteBatch::Iterate will try with a larger sequence number if the memtable reports a duplicate. This status is specified with TryAgain status. So far the assumption was that the last entry in the batch will never return TryAgain, which is correct when WAL is created via WritePrepared since it always appends a batch separator if a natural one does not exist. However when reading a WAL generated by WriteCommitted this batch separator might not exist. Although WritePrepared is not supposed to be able to read the WAL generated by WriteCommitted we should avoid confusing scenarios in which the behavior becomes unpredictable. The path fixes that by allowing TryAgain even for the last entry of the write batch.
Closes https://github.com/facebook/rocksdb/pull/3747
Differential Revision: D7708391
Pulled By: maysamyabandeh
fbshipit-source-id: bfaddaa9b14a4cdaff6977f6f63c789a6ab1ee0d
Summary:
Fix the following gcc-8 warnings:
- conflicting C language linkage declaration [-Werror]
- writing to an object with no trivial copy-assignment [-Werror=class-memaccess]
- array subscript -1 is below array bounds [-Werror=array-bounds]
Solves https://github.com/facebook/rocksdb/issues/3716
Closes https://github.com/facebook/rocksdb/pull/3736
Differential Revision: D7684161
Pulled By: yiwu-arbug
fbshipit-source-id: 47c0423d26b74add251f1d3595211eee1e41e54a
Summary:
Right now in `SyncClosedLogs`, `CopyFile`, and `AddRecord`, where `Sync` and `Append` are invoked in a loop, the error status are not checked. This could lead to potential corruption as later calls will overwrite the error status.
Closes https://github.com/facebook/rocksdb/pull/3740
Differential Revision: D7678848
Pulled By: miasantreble
fbshipit-source-id: 4b0b412975989dfe80348f73217b9c4122a4bd77
Summary:
The reason for this initialization is that LLVM UBSAN check will fail due to
uninitialized bool. [StackOverflow post](https://stackoverflow.com/questions/31420154/runtime-error-load-of-value-127-which-is-not-a-valid-value-for-type-bool).
UBSAN log:
> ===== Running external_sst_file_basic_test
[==========] Running 7 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 7 tests from ExternalSSTFileBasicTest
[ RUN ] ExternalSSTFileBasicTest.Basic
[ OK ] ExternalSSTFileBasicTest.Basic (6 ms)
[ RUN ] ExternalSSTFileBasicTest.NoCopy
db/external_sst_file_ingestion_job.h:23:8: runtime error: load of value 253, which is not a valid value for type 'bool'
miasantreble I've tested this locally using the following command.
```
TEST_TMPDIR=/dev/shm/rocksdb COMPILE_WITH_UBSAN=1 OPT=-g make J=1 -j8 ubsan_check
```
ajkr This PR is related to your review comment in [PR](https://github.com/facebook/rocksdb/pull/3713/). It turns out that, with UBSAN enabled, we must provide a default value for boolean member variables.
Closes https://github.com/facebook/rocksdb/pull/3728
Differential Revision: D7642476
Pulled By: riversand963
fbshipit-source-id: 4c09a4b8d271151cb99ae7393db9e4ad9f29762e
Summary:
this PR fixes a few failed contbuild:
1. ASAN memory leak in Block::NewIterator (table/block.cc:429). the proper destruction of first_level_iter_ and second_level_iter_ of two_level_iterator.cc is missing from the code after the refactoring in https://github.com/facebook/rocksdb/pull/3406
2. various unused param errors introduced by https://github.com/facebook/rocksdb/pull/3662
3. updated comment for `ForceReleaseCachedEntry` to emphasize the use of `force_erase` flag.
Closes https://github.com/facebook/rocksdb/pull/3718
Reviewed By: maysamyabandeh
Differential Revision: D7621192
Pulled By: miasantreble
fbshipit-source-id: 476c94264083a0730ded957c29de7807e4f5b146
Summary:
When there are many range deletions in a range, we want to trigger manual compaction on this range to reclaim disk space as soon as possible and speed up read.
After this change, we can collect informations of range deletions and store them into user properties which can guide our manual compaction.
Closes https://github.com/facebook/rocksdb/pull/3695
Differential Revision: D7570322
Pulled By: ajkr
fbshipit-source-id: c358fa43b0aac6cc954d2eadc7d3bd8015373369
Summary:
RocksDB supports ingestion of external ssts. If ingestion_options.move_files is true, when performing ingestion, RocksDB first tries to link external ssts. If external SST file resides on a different FS, or the underlying FS does not support hard link, then RocksDB performs actual file copy. However, no matter which choice is made, current code increase bytes-written when updating compaction stats, which is inaccurate when RocksDB does NOT copy file.
Rename a sync point.
Closes https://github.com/facebook/rocksdb/pull/3713
Differential Revision: D7604151
Pulled By: riversand963
fbshipit-source-id: dd0c0d9b9a69c7d9ffceafc3d9c23371aa413586
Summary:
This PR comments out the rest of the unused arguments which allow us to turn on the -Wunused-parameter flag. This is the second part of a codemod relating to https://github.com/facebook/rocksdb/pull/3557.
Closes https://github.com/facebook/rocksdb/pull/3662
Differential Revision: D7426121
Pulled By: Dayvedde
fbshipit-source-id: 223994923b42bd4953eb016a0129e47560f7e352
Summary:
Add `compaction_reason` as part of event log for event `compaction started`.
Add counters for each `CompactionReason`.
Closes https://github.com/facebook/rocksdb/pull/3679
Differential Revision: D7550348
Pulled By: riversand963
fbshipit-source-id: a19cff3a678c785aa5ef41aac78b9a5968fcc34d
Summary:
In `cf_options_type_info`, the deprecated options are all considered to have offset zero in the `MutableCFOptions` struct. Previously we weren't checking in `GetMutableOptionsFromStrings` whether the provided option was deprecated or not and simply writing the provided value to the offset specified by `cf_options_type_info`. That meant setting any deprecated option would overwrite the first element in the struct, which is `write_buffer_size`. `db_stress` hit this often since it calls `SetOptions` with `soft_rate_limit=0` and `hard_rate_limit=0`, which are both deprecated so cause `write_buffer_size` to be set to zero, which causes it to crash on the following assertion:
```
db_stress: db/memtable.cc:106: rocksdb::MemTable::MemTable(const rocksdb::InternalKeyComparator&, const rocksdb::ImmutableCFOptions&, const rocksdb::MutableCFOptions&, rocksdb::WriteBufferManager*, rocksdb::SequenceNumber, uint32_t): Assertion `!ShouldScheduleFlush()' failed.
```
We fix it by skipping deprecated options (and logging a warning) when users provide them to `SetOptions`. I didn't want to fail the call for compatibility reasons.
Closes https://github.com/facebook/rocksdb/pull/3700
Differential Revision: D7572596
Pulled By: ajkr
fbshipit-source-id: bd5d84e14c0c39f30c5d4c6df7c1503d2c28ecf1
Summary:
1. Remove redundant text.
2. Make terminology consistent across all comments and doc of RocksDB. Also do
our best to conform to conventions. Specifically, use 'callback' instead of
'call-back' [wikipedia](https://en.wikipedia.org/wiki/Callback_(computer_programming)).
Closes https://github.com/facebook/rocksdb/pull/3693
Differential Revision: D7560396
Pulled By: riversand963
fbshipit-source-id: ba8c251c487f4e7d1872a1a8dc680f9e35a6ffb8
Summary:
In this case, we add input files of compaction, not outputs.
Closes https://github.com/facebook/rocksdb/pull/3686
Differential Revision: D7556781
Pulled By: ajkr
fbshipit-source-id: ae135bb6eda60db8f275a9ba2d21c18aaadef5b7
Summary:
- inflate the argument passed as `max_compact_bytes_per_del_file` by a bit (10%). The intent of this argument is prevent L0 files from being intra-L0 compacted multiple times. Without compression, some intra-L0 compactions exceed this limit (and thus aren't executed), even though none of their files have gone through intra-L0 before.
- fix `FindIntraL0Compaction` as it was rejecting some valid intra-L0 compactions. In particular, `compact_bytes_per_del_file` is the work-per-deleted-file for the span [0, span_len), whereas `new_compact_bytes_per_del_file` is the work-per-deleted-file for the span [0, span_len+1). The former is more correct for checking whether we've found an eligible span.
Closes https://github.com/facebook/rocksdb/pull/3684
Differential Revision: D7530396
Pulled By: ajkr
fbshipit-source-id: cad4f50902bdc428ac9ff6fffb13eb288648d85e
Summary:
Adding some stats that would be helpful to monitor if the DB has gone to unlikely stats that would hurt the performance. These are mostly when we end up needing to acquire a mutex.
Closes https://github.com/facebook/rocksdb/pull/3683
Differential Revision: D7529393
Pulled By: maysamyabandeh
fbshipit-source-id: f7d36279a8f39bd84d8ddbf64b5c97f670c5d6d9
Summary:
In this change, an option to set different paths for different column families is added.
This option is set via cf_paths setting of ColumnFamilyOptions. This option will work in a similar fashion to db_paths setting. Cf_paths is a vector of Dbpath values which contains a pair of the absolute path and target size. Multiple levels in a Column family can go to different paths if cf_paths has more than one path.
To maintain backward compatibility, if cf_paths is not specified for a column family, db_paths setting will be used. Note that, if db_paths setting is also not specified, RocksDB already has code to use db_name as the only path.
Changes :
1) A new member "cf_paths" is added to ImmutableCfOptions. This is set, based on cf_paths setting of ColumnFamilyOptions and db_paths setting of ImmutableDbOptions. This member is used to identify the path information whenever files are accessed.
2) Validation checks are added for cf_paths setting based on existing checks for db_paths setting.
3) DestroyDB, PurgeObsoleteFiles etc. are edited to support multiple cf_paths.
4) Unit tests are added appropriately.
Closes https://github.com/facebook/rocksdb/pull/3102
Differential Revision: D6951697
Pulled By: ajkr
fbshipit-source-id: 60d2262862b0a8fd6605b09ccb0da32bb331787d
Summary:
Primitive types constness does not affect the signature of the
method and has no influence on whether the overriding method would
actually have that const bool instead of just bool. In addition,
it is rarely useful but does produce a compatibility warnings
in VS 2015 compiler.
Closes https://github.com/facebook/rocksdb/pull/3663
Differential Revision: D7475739
Pulled By: ajkr
fbshipit-source-id: fb275378b5acc397399420ae6abb4b6bfe5bd32f
Summary:
currently rocksdb lite build fails due to the following errors:
> db/db_sst_test.cc:29:51: error: ‘FlushJobInfo’ does not name a type
virtual void OnFlushCompleted(DB* /*db*/, const FlushJobInfo& info) override {
^
db/db_sst_test.cc:29:16: error: ‘virtual void rocksdb::FlushedFileCollector::OnFlushCompleted(rocksdb::DB*, const int&)’ marked ‘override’, but does not override
virtual void OnFlushCompleted(DB* /*db*/, const FlushJobInfo& info) override {
^
db/db_sst_test.cc:24:7: error: ‘class rocksdb::FlushedFileCollector’ has virtual functions and accessible non-virtual destructor [-Werror=non-virtual-dtor]
class FlushedFileCollector : public EventListener {
^
db/db_sst_test.cc: In member function ‘virtual void rocksdb::FlushedFileCollector::OnFlushCompleted(rocksdb::DB*, const int&)’:
db/db_sst_test.cc:31:35: error: request for member ‘file_path’ in ‘info’, which is of non-class type ‘const int’
flushed_files_.push_back(info.file_path);
^
cc1plus: all warnings being treated as errors
make: *** [db/db_sst_test.o] Error 1
Closes https://github.com/facebook/rocksdb/pull/3676
Differential Revision: D7493006
Pulled By: miasantreble
fbshipit-source-id: 77dff0a5b23e27db51be9b9798e3744e6fdec64f
Summary:
Ttl-triggered and snapshot-release-triggered compactions should not be considered as manual compactions. This is a bug.
Closes https://github.com/facebook/rocksdb/pull/3678
Differential Revision: D7498151
Pulled By: sagar0
fbshipit-source-id: a2d5bed05268a4dc93d54ea97a9ae44b366df15d
Summary:
Level Compaction with TTL.
As of today, a file could exist in the LSM tree without going through the compaction process for a really long time if there are no updates to the data in the file's key range. For example, in certain use cases, the keys are not actually "deleted"; instead they are just set to empty values. There might not be any more writes to this "deleted" key range, and if so, such data could remain in the LSM for a really long time resulting in wasted space.
Introducing a TTL could solve this problem. Files (and, in turn, data) older than TTL will be scheduled for compaction when there is no other background work. This will make the data go through the regular compaction process and get rid of old unwanted data.
This also has the (good) side-effect of all the data in the non-bottommost level being newer than ttl, and all data in the bottommost level older than ttl. It could lead to more writes while reducing space.
This functionality can be controlled by the newly introduced column family option -- ttl.
TODO for later:
- Make ttl mutable
- Extend TTL to Universal compaction as well? (TTL is already supported in FIFO)
- Maybe deprecate CompactionOptionsFIFO.ttl in favor of this new ttl option.
Closes https://github.com/facebook/rocksdb/pull/3591
Differential Revision: D7275442
Pulled By: sagar0
fbshipit-source-id: dcba484717341200d419b0953dafcdf9eb2f0267
Summary:
The is an optimization to reduce lookup in the CommitCache when querying IsInSnapshot. The optimization takes the smallest uncommitted data at the time that the snapshot was taken and if the sequence number of the read data is lower than that number it assumes the data as committed.
To implement this optimization two changes are required: i) The AddPrepared function must be called sequentially to avoid out of order insertion in the PrepareHeap (otherwise the top of the heap does not indicate the smallest prepare in future too), ii) non-2PC transactions also call AddPrepared if they do not commit in one step.
Closes https://github.com/facebook/rocksdb/pull/3649
Differential Revision: D7388630
Pulled By: maysamyabandeh
fbshipit-source-id: b79506238c17467d590763582960d4d90181c600
Summary:
Manual compactions should be cancelled, just like scheduled compactions are cancelled, if sfm->EnoughRoomForCompaction is not true.
Closes https://github.com/facebook/rocksdb/pull/3670
Differential Revision: D7457683
Pulled By: amytai
fbshipit-source-id: 669b02fdb707f75db576d03d2c818fb98d1876f5
Summary:
This patch record the deleted WAL numbers in the manifest to ignore them and any WAL older than them during recovery. This is to avoid scenarios when we have a gap between the WAL files are fed to the recovery procedure. The gap could happen by for example out-of-order WAL deletion. Such gap could cause problems in 2PC recovery where the prepared and commit entry are placed into two separate WAL and gap in the WALs could result into not processing the WAL with the commit entry and hence breaking the 2PC recovery logic.
Closes https://github.com/facebook/rocksdb/pull/3488
Differential Revision: D6967893
Pulled By: maysamyabandeh
fbshipit-source-id: 13119feb155a08ab6d4909f437c7a750480dc8a1
Summary:
When using two_write_queue, the published seq and the last allocated sequence could be ahead of the LastSequence, even if both write queues are stopped as in WriteRecoverableState. The patch fixes a bug in WriteRecoverableState in which LastSequence was used as a reference but the result was applied to last fetched sequence and last published seq.
Closes https://github.com/facebook/rocksdb/pull/3665
Differential Revision: D7446099
Pulled By: maysamyabandeh
fbshipit-source-id: 1449bed9aed8e9db6af85946efd347cb8efd3c0b
Summary:
Currently if the CommitTimeWriteBatch is set to be used only as a state that is required only for recovery , the user cannot see that in DB until it is restarted. This while the state is already inserted into the DB after the memtable flush. It would be useful for debugging if make this state visible to the user after the flush by committing it. The patch does it by a invoking a callback that does the commit on the recoverable state.
Closes https://github.com/facebook/rocksdb/pull/3661
Differential Revision: D7424577
Pulled By: maysamyabandeh
fbshipit-source-id: 137f9408662f0853938b33fa440f27f04c1bbf5c
Summary:
Possible interleaved execution of background compaction thread calling `FindObsoleteFiles (no full scan) / PurgeObsoleteFiles` and user thread calling `FindObsoleteFiles (full scan) / PurgeObsoleteFiles` can lead to race condition on which RocksDB attempts to delete a file twice. The second attempt will fail and return `IO error`. This may occur to other files, but this PR targets sst.
Also add a unit test to verify that this PR fixes the issue.
The newly added unit test `obsolete_files_test` has a test case for this scenario, implemented in `ObsoleteFilesTest#RaceForObsoleteFileDeletion`. `TestSyncPoint`s are used to coordinate the interleaving the `user_thread` and background compaction thread. They execute as follows
```
timeline user_thread background_compaction thread
t1 | FindObsoleteFiles(full_scan=false)
t2 | FindObsoleteFiles(full_scan=true)
t3 | PurgeObsoleteFiles
t4 | PurgeObsoleteFiles
V
```
When `user_thread` invokes `FindObsoleteFiles` with full scan, it collects ALL files in RocksDB directory, including the ones that background compaction thread have collected in its job context. Then `user_thread` will see an IO error when trying to delete these files in `PurgeObsoleteFiles` because background compaction thread has already deleted the file in `PurgeObsoleteFiles`.
To fix this, we make RocksDB remember which (SST) files have been found by threads after calling `FindObsoleteFiles` (see `DBImpl#files_grabbed_for_purge_`). Therefore, when another thread calls `FindObsoleteFiles` with full scan, it will not collect such files.
ajkr could you take a look and comment? Thanks!
Closes https://github.com/facebook/rocksdb/pull/3638
Differential Revision: D7384372
Pulled By: riversand963
fbshipit-source-id: 01489516d60012e722ee65a80e1449e589ce26d3
Summary:
Currently log_writer->AddRecord in WriteImpl is protected from concurrent calls via FlushWAL only if two_write_queues_ option is set. The patch fixes the problem by i) skip log_writer->AddRecord in FlushWAL if manual_wal_flush is not set, ii) protects log_writer->AddRecord in WriteImpl via log_write_mutex_ if manual_wal_flush_ is set but two_write_queues_ is not.
Fixes#3599
Closes https://github.com/facebook/rocksdb/pull/3656
Differential Revision: D7405608
Pulled By: maysamyabandeh
fbshipit-source-id: d6cc265051c77ae49c7c6df4f427350baaf46934
Summary:
Currently AddPrepared is performed only on the first sub-batch if there are duplicate keys in the write batch. This could cause a problem if the transaction takes too long to commit and the seq number of the first sub-patch moved to old_prepared_ but not the seq of the later ones. The patch fixes this by calling AddPrepared for all sub-patches.
Closes https://github.com/facebook/rocksdb/pull/3651
Differential Revision: D7388635
Pulled By: maysamyabandeh
fbshipit-source-id: 0ccd80c150d9bc42fe955e49ddb9d7ca353067b4
Summary:
RangeDelAggregator will remember the files whose range tombstones have been added,
so the caller can check whether the file has been added before call AddTombstones.
Closes https://github.com/facebook/rocksdb/pull/3635
Differential Revision: D7354604
Pulled By: ajkr
fbshipit-source-id: 9b9f7ec130556028df417e650711554b46d8d107
Summary:
Summary
========
`InlineSkipList<>::Insert` takes the `key` parameter as a C-string. Then, it performs multiple comparisons with it requiring the `GetLengthPrefixedSlice()` to be spawn in `MemTable::KeyComparator::operator()(const char* prefix_len_key1, const char* prefix_len_key2)` on the same data over and over. The patch tries to optimize that.
Rough performance comparison
=====
Big keys, no compression.
```
$ ./db_bench --writes 20000000 --benchmarks="fillrandom" --compression_type none -key_size 256
(...)
fillrandom : 4.222 micros/op 236836 ops/sec; 80.4 MB/s
```
```
$ ./db_bench --writes 20000000 --benchmarks="fillrandom" --compression_type none -key_size 256
(...)
fillrandom : 4.064 micros/op 246059 ops/sec; 83.5 MB/s
```
TODO
======
In ~~a separated~~ this PR:
- [x] Go outside the write path. Maybe even eradicate the C-string-taking variant of `KeyIsAfterNode` entirely.
- [x] Try to cache the transformations applied by `KeyComparator` & friends in situations where we havy many comparisons with the same key.
Closes https://github.com/facebook/rocksdb/pull/3516
Differential Revision: D7059300
Pulled By: ajkr
fbshipit-source-id: 6f027dbb619a488129f79f79b5f7dbe566fb2dbb
Summary:
Fsync after writing global sequence number to the ingestion file in ExternalSstFileIngestionJob. Otherwise the file metadata could be incorrect.
Closes https://github.com/facebook/rocksdb/pull/3644
Differential Revision: D7373813
Pulled By: sagar0
fbshipit-source-id: 4da2c9e71a8beb5c08b4ac955f288ee1576358b8
Summary:
It was misnamed. It actually updates `bg_error_` if `PreprocessWrite()` or `WriteToWAL()` fail, not related to the user callback.
Closes https://github.com/facebook/rocksdb/pull/3485
Differential Revision: D6955787
Pulled By: ajkr
fbshipit-source-id: bd7afc3fdb7a52830c021cbfc25fcbc3ab7d5e10
Summary:
This commit fixes a race condition on calling SetLastPublishedSequence. The function must be called only from the 2nd write queue when two_write_queues is enabled. However there was a bug that would also call it from the main write queue if CommitTimeWriteBatch is provided to the commit request and yet use_only_the_last_commit_time_batch_for_recovery optimization is not enabled. To fix that we penalize the commit request in such cases by doing an additional write solely to publish the seq number from the 2nd queue.
Closes https://github.com/facebook/rocksdb/pull/3641
Differential Revision: D7361508
Pulled By: maysamyabandeh
fbshipit-source-id: bf8f7a27e5cccf5425dccbce25eb0032e8e5a4d7
Summary:
This pull request exposes the interface of PerfContext as C API
Closes https://github.com/facebook/rocksdb/pull/3607
Differential Revision: D7294225
Pulled By: ajkr
fbshipit-source-id: eddcfbc13538f379950b2c8b299486695ffb5e2c
Summary:
When destorying column family handle after the column family has been deleted, the handle may hold share pointers of some objects in ColumnFamilyOptions, but in the destructor, the destructing order may cause some of the objects to be destoryed before being used by the following steps. Fix it by making a copy of the option object and destory it as the last step.
Closes https://github.com/facebook/rocksdb/pull/3610
Differential Revision: D7281025
Pulled By: siying
fbshipit-source-id: ac18f3b2841788cba4ccfa1abd8d59158c1113bc
Summary:
Previously, the compaction in `DBCompactionTestWithParam.ForceBottommostLevelCompaction` generated multiple files in no-compression use case, andone file in compression use case. I increased `target_file_size_base` so it generates one file in both use cases.
Closes https://github.com/facebook/rocksdb/pull/3625
Differential Revision: D7311885
Pulled By: ajkr
fbshipit-source-id: 97f249fa83a9924ac34357a4bb3189c969ecb107
Summary:
If there are a lot of overlapped files in L0, creating a merging iterator for
all files in L0 to check overlap can be very slow because we need to read and
seek all files in L0. However, in that case, the ingested file is likely to
overlap with some files in L0, so if we check those files one by one, we can stop
once we encounter overlap.
Ref: https://github.com/facebook/rocksdb/issues/3540
Closes https://github.com/facebook/rocksdb/pull/3564
Differential Revision: D7196784
Pulled By: anand1976
fbshipit-source-id: 8700c1e903bd515d0fa7005b6ce9b3a3d9db2d67
