Summary:
A vector that leverages pre-allocated stack-based array to achieve better
performance for array with small amount of items.

Test Plan:
Added tests for both correctness and performance

Here is the performance benchmark between vector and autovector

Please note that in the test "Creation and Insertion Test", the test case were designed with the motivation described below:

* no element inserted: internal array of std::vector may not really get
  initialize.
* one element inserted: internal array of std::vector must have
  initialized.
* kSize elements inserted. This shows the most time we'll spend if we
  keep everything in stack.
* 2 * kSize elements inserted. The internal vector of
  autovector must have been initialized.

Note: kSize is the capacity of autovector

  =====================================================
  Creation and Insertion Test
  =====================================================
  created 100000 vectors:
  	each was inserted with 0 elements
  	total time elapsed: 128000 (ns)
  created 100000 autovectors:
  	each was inserted with 0 elements
  	total time elapsed: 3641000 (ns)
  created 100000 VectorWithReserveSizes:
  	each was inserted with 0 elements
  	total time elapsed: 9896000 (ns)
  -----------------------------------
  created 100000 vectors:
  	each was inserted with 1 elements
  	total time elapsed: 11089000 (ns)
  created 100000 autovectors:
  	each was inserted with 1 elements
  	total time elapsed: 5008000 (ns)
  created 100000 VectorWithReserveSizes:
  	each was inserted with 1 elements
  	total time elapsed: 24271000 (ns)
  -----------------------------------
  created 100000 vectors:
  	each was inserted with 4 elements
  	total time elapsed: 39369000 (ns)
  created 100000 autovectors:
  	each was inserted with 4 elements
  	total time elapsed: 10121000 (ns)
  created 100000 VectorWithReserveSizes:
  	each was inserted with 4 elements
  	total time elapsed: 28473000 (ns)
  -----------------------------------
  created 100000 vectors:
  	each was inserted with 8 elements
  	total time elapsed: 75013000 (ns)
  created 100000 autovectors:
  	each was inserted with 8 elements
  	total time elapsed: 18237000 (ns)
  created 100000 VectorWithReserveSizes:
  	each was inserted with 8 elements
  	total time elapsed: 42464000 (ns)
  -----------------------------------
  created 100000 vectors:
  	each was inserted with 16 elements
  	total time elapsed: 102319000 (ns)
  created 100000 autovectors:
  	each was inserted with 16 elements
  	total time elapsed: 76724000 (ns)
  created 100000 VectorWithReserveSizes:
  	each was inserted with 16 elements
  	total time elapsed: 68285000 (ns)
  -----------------------------------
  =====================================================
  Sequence Access Test
  =====================================================
  performed 100000 sequence access against vector
  	size: 4
  	total time elapsed: 198000 (ns)
  performed 100000 sequence access against autovector
  	size: 4
  	total time elapsed: 306000 (ns)
  -----------------------------------
  performed 100000 sequence access against vector
  	size: 8
  	total time elapsed: 565000 (ns)
  performed 100000 sequence access against autovector
  	size: 8
  	total time elapsed: 512000 (ns)
  -----------------------------------
  performed 100000 sequence access against vector
  	size: 16
  	total time elapsed: 1076000 (ns)
  performed 100000 sequence access against autovector
  	size: 16
  	total time elapsed: 1070000 (ns)
  -----------------------------------

Reviewers: dhruba, haobo, sdong, chip

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14655

Only try to use fallocate if it's actually present on the system.

Summary:
Add a pointer to the engineering design discussion forum.

Test Plan:

Reviewers:

CC:

Task ID: #

Blame Rev:

Summary:
Instead of locking and saving a DB state, we can cache a DB state and update it only when it changes. This change reduces lock contention and speeds up read operations on the DB.

Performance improvements are substantial, although there is some cost in no-read workloads. I ran the regression tests on my devserver and here are the numbers:

  overwrite                    56345  ->   63001
  fillseq                      193730 ->  185296
  readrandom                   771301 -> 1219803 (58% improvement!)
  readrandom_smallblockcache   677609 ->  862850
  readrandom_memtable_sst      710440 -> 1109223
  readrandom_fillunique_random 221589 ->  247869
  memtablefillrandom           105286 ->   92643
  memtablereadrandom           763033 -> 1288862

Test Plan:
make asan_check
I am also running db_stress

Reviewers: dhruba, haobo, sdong, kailiu

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14679

fix missing gflags library

Summary:
For some tests I want to cache the database prior to running other tests on the same invocation
of db_bench. The readtocache test ignores --threads and --reads so those can be used by other tests
and it will still do a full read of --num rows with one thread. It might be invoked like:
  db_bench --benchmarks=readtocache,readrandom --reads 100 --num 10000 --threads 8

Task ID: #

Blame Rev:

Test Plan:
run db_bench

Revert Plan:

Database Impact:

Memcache Impact:

Other Notes:

EImportant:

- begin *PUBLIC* platform impact section -
Bugzilla: #
- end platform impact -

Reviewers: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14739

Summary:
db_test should be the first to execute because it finds the most bugs.

Also, when third parties report issues, we don't want ldb error message, we prefer to have db_test error message. For example, see thread: https://github.com/facebook/rocksdb/issues/25

Test Plan: make check

Reviewers: dhruba, haobo, kailiu

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14715

Remove utilities/.DS_Store file.

C bindings: add a bunch of the newer options

Summary: I realized that "D14409 Avoid sorting in Version::Get() by presorting them in VersionSet::Builder::SaveTo()" is not done in an optimized place. SaveTo() is usually inside mutex. Move it to Finalize(), which is called out of mutex.

Test Plan: make all check

Reviewers: dhruba, haobo, kailiu

Reviewed By: dhruba

CC: igor, leveldb

Differential Revision: https://reviews.facebook.net/D14607

Summary: It seems to be a decision tradeoff in current codes: we make a malloc for every Get() to reduce one malloc for a flush inside mutex. It takes about 5% of CPU time in readrandom tests. We might consider the tradeoff to be the other way around.

Test Plan: make all check

Reviewers: dhruba, haobo, igor

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14697

Summary:
I realized that manifest will get deleted by PurgeObsoleteFiles in DBImpl, but it is sill cleaner to delete
files before we restore the backup

Test Plan: backupable_db_test

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14619

Summary:
Adds these counters
{ WAL_FILE_SYNCED, "rocksdb.wal.synced" }
  number of writes that request a WAL sync
{ WAL_FILE_BYTES, "rocksdb.wal.bytes" },
  number of bytes written to the WAL
{ WRITE_DONE_BY_SELF, "rocksdb.write.self" },
  number of writes processed by the calling thread
{ WRITE_DONE_BY_OTHER, "rocksdb.write.other" },
  number of writes not processed by the calling thread. Instead these were
  processed by the current holder of the write lock
{ WRITE_WITH_WAL, "rocksdb.write.wal" },
  number of writes that request WAL logging
{ COMPACT_READ_BYTES, "rocksdb.compact.read.bytes" },
  number of bytes read during compaction
{ COMPACT_WRITE_BYTES, "rocksdb.compact.write.bytes" },
  number of bytes written during compaction

Per-interval stats output was updated with WAL stats and correct stats for universal compaction
including a correct value for write-amplification. It now looks like:
                               Compactions
Level  Files Size(MB) Score Time(sec)  Read(MB) Write(MB)    Rn(MB)  Rnp1(MB)  Wnew(MB) RW-Amplify Read(MB/s) Write(MB/s)      Rn     Rnp1     Wnp1     NewW    Count  Ln-stall Stall-cnt
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  0        7      464  46.4       281      3411      3875      3411         0      3875        2.1      12.1        13.8      621        0      240      240      628       0.0         0
Uptime(secs): 310.8 total, 2.0 interval
Writes cumulative: 9999999 total, 9999999 batches, 1.0 per batch, 1.22 ingest GB
WAL cumulative: 9999999 WAL writes, 9999999 WAL syncs, 1.00 writes per sync, 1.22 GB written
Compaction IO cumulative (GB): 1.22 new, 3.33 read, 3.78 write, 7.12 read+write
Compaction IO cumulative (MB/sec): 4.0 new, 11.0 read, 12.5 write, 23.4 read+write
Amplification cumulative: 4.1 write, 6.8 compaction
Writes interval: 100000 total, 100000 batches, 1.0 per batch, 12.5 ingest MB
WAL interval: 100000 WAL writes, 100000 WAL syncs, 1.00 writes per sync, 0.01 MB written
Compaction IO interval (MB): 12.49 new, 14.98 read, 21.50 write, 36.48 read+write
Compaction IO interval (MB/sec): 6.4 new, 7.6 read, 11.0 write, 18.6 read+write
Amplification interval: 101.7 write, 102.9 compaction
Stalls(secs): 142.924 level0_slowdown, 0.000 level0_numfiles, 0.805 memtable_compaction, 0.000 leveln_slowdown
Stalls(count): 132461 level0_slowdown, 0 level0_numfiles, 3 memtable_compaction, 0 leveln_slowdown

Task ID: #3329644, #3301695

Blame Rev:

Test Plan:
Revert Plan:

Database Impact:

Memcache Impact:

Other Notes:

EImportant:

- begin *PUBLIC* platform impact section -
Bugzilla: #
- end platform impact -

Reviewers: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14583

Summary: @MarkCallaghan's tests indicate that performance with 8k rows in memtable is much worse than empty memtable. I wanted to add a regression tests that measures this effect, so we could optimize it. However, current config shows 634461 QPS on my devbox. Mark, any idea why this is so much faster than your measurements?

Test Plan: Ran the regression test.

Reviewers: MarkCallaghan, dhruba, haobo

Reviewed By: MarkCallaghan

CC: leveldb, MarkCallaghan

Differential Revision: https://reviews.facebook.net/D14511

Summary: In get operations, merge_operands is only used in few cases. Lazily initialize it can reduce average latency in some cases

Test Plan: make all check

Reviewers: haobo, kailiu, dhruba

Reviewed By: haobo

CC: igor, nkg-, leveldb

Differential Revision: https://reviews.facebook.net/D14415

Conflicts:
	db/db_impl.cc
	db/memtable.cc

[RocksDB Performance Branch] Avoid sorting in Version::Get() by presorting them in VersionSet::Builder::SaveTo()

Summary: Pre-sort files in VersionSet::Builder::SaveTo() so that when getting the value, no need to sort them. It can avoid the costs of vector operations and sorting in Version::Get().

Test Plan: make all check

Reviewers: haobo, kailiu, dhruba

Reviewed By: dhruba

CC: nkg-, igor, leveldb

Differential Revision: https://reviews.facebook.net/D14409

Summary:
creating new iterators of mem tables can be expensive. Move them out of mutex.
DBImpl::WriteLevel0Table()'s mems seems to be a local vector and is only used by flushing. memtables to flush are also immutable, so it should be safe to do so.

Test Plan: make all check

Reviewers: haobo, dhruba, kailiu

Reviewed By: dhruba

CC: igor, leveldb

Differential Revision: https://reviews.facebook.net/D14577

Conflicts:
	db/db_impl.cc

Summary:
I have ran a get benchmark where all the data is in the cache and observed that most of the time is spent on waiting for lock in LRUCache.

This is an effort to optimize LRUCache.

Test Plan:
The data was loaded with fillseq. Then, I ran a benchmark:

    /db_bench --db=/tmp/rocksdb_stat_bench --num=1000000 --benchmarks=readrandom --statistics=1 --use_existing_db=1 --threads=16 --disable_seek_compaction=1 --cache_size=20000000000 --cache_numshardbits=8 --table_cache_numshardbits=8

I ran the benchmark three times. Here are the results:
AFTER THE PATCH: 798072, 803998, 811807
BEFORE THE PATCH: 782008, 815593, 763017

Reviewers: dhruba, haobo, kailiu

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14571

Summary: We now delete backups with newer sequence number, so the clients don't have to handle confusing situations when they restore from backup.

Test Plan: added a unit test

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14547

Summary: So fflush() takes a lock which is heavyweight. I added flush_pending_, but more importantly, I removed LogFlush() from foreground threads.

Test Plan: ./db_test

Reviewers: dhruba, haobo

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14535

Summary: Valgrind complained about BackupableDB. This fixes valgrind errors. Also, I cleaned up some code.

Test Plan: valgrind does not complain anymore

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14529

Build shared lib and put linker flags to the end

Rename leveldb to rocksdb in C api

Summary:
In this diff I present you BackupableDB v1. You can easily use it to backup your DB and it will do incremental snapshots for you.
Let's first describe how you would use BackupableDB. It's inheriting StackableDB interface so you can easily construct it with your DB object -- it will add a method RollTheSnapshot() to the DB object. When you call RollTheSnapshot(), current snapshot of the DB will be stored in the backup dir. To restore, you can just call RestoreDBFromBackup() on a BackupableDB (which is a static method) and it will restore all files from the backup dir. In the next version, it will even support automatic backuping every X minutes.

There are multiple things you can configure:
1. backup_env and db_env can be different, which is awesome because then you can easily backup to HDFS or wherever you feel like.
2. sync - if true, it *guarantees* backup consistency on machine reboot
3. number of snapshots to keep - this will keep last N snapshots around if you want, for some reason, be able to restore from an earlier snapshot. All the backuping is done in incremental fashion - if we already have 00010.sst, we will not copy it again. *IMPORTANT* -- This is based on assumption that 00010.sst never changes - two files named 00010.sst from the same DB will always be exactly the same. Is this true? I always copy manifest, current and log files.
4. You can decide if you want to flush the memtables before you backup, or you're fine with backing up the log files -- either way, you get a complete and consistent view of the database at a time of backup.
5. More things you can find in BackupableDBOptions

Here is the directory structure I use:

   backup_dir/CURRENT_SNAPSHOT - just 4 bytes holding the latest snapshot
               0, 1, 2, ... - files containing serialized version of each snapshot - containing a list of files
               files/*.sst - sst files shared between snapshots - if one snapshot references 00010.sst and another one needs to backup it from the DB, it will just reference the same file
               files/ 0/, 1/, 2/, ... - snapshot directories containing private snapshot files - current, manifest and log files

All the files are ref counted and deleted immediatelly when they get out of scope.

Some other stuff in this diff:
1. Added GetEnv() method to the DB. Discussed with @haobo and we agreed that it seems right thing to do.
2. Fixed StackableDB interface. The way it was set up before, I was not able to implement BackupableDB.

Test Plan:
I have a unittest, but please don't look at this yet. I just hacked it up to help me with debugging. I will write a lot of good tests and update the diff.

Also, `make asan_check`

Reviewers: dhruba, haobo, emayanke

Reviewed By: dhruba

CC: leveldb, haobo

Differential Revision: https://reviews.facebook.net/D14295

Branch detection did not work in Jenkins. I realized that it set
GIT_BRANCH env variable to point to the current branch, so let's try
using this for branch detection.

Summary:
This will help me a lot! When we hit an assertion in unittest, we get the whole stack trace now.

Also, changed stack trace a bit, we now include actual demangled C++ class::function symbols!

Test Plan: Added ASSERT_TRUE(false) to a test, observed a stack trace

Reviewers: haobo, dhruba, kailiu

Reviewed By: kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14499

Summary: When running regression tests on other branches, this will push values to entity rocksdb_build.$git_branch

Test Plan: Ran regression test on regression branch, observed values send to ODS in entity rocksdb_build.regression

Reviewers: kailiu

Reviewed By: kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14493

Summary: Now DBWithTTL takes DB* and can behave more like StackableDB. This saves us a lot of duplicate work by defining interfaces

Test Plan: ttl_test with ASAN - OK

Reviewers: emayanke

Reviewed By: emayanke

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14481