Commit Graph

327 Commits

Author SHA1 Message Date
Igor Canadi 0c26e76b28 Merge pull request #237 from tdfischer/tdfischer/faster-timeout-test
test: db: fix test to have a smaller timeout for when it runs on faster ...
2014-08-28 20:40:10 -04:00
Radheshyam Balasundaram b6fd7811eb Don't do memtable lookup in db_impl_readonly if memtables are empty while opening db.
Summary: In DBImpl::Recover method, while loading memtables, also check if memtables are empty. Use this in DBImplReadonly to determine whether to lookup memtable or not.

Test Plan:
db_test
make check all

Reviewers: sdong, yhchiang, ljin, igor

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22281
2014-08-26 17:19:03 -07:00
Stanislau Hlebik 9dcb75b6d9 Add is-file-deletions-enabled property
Summary:
Add property 'rocksdb.is-file-deletions-enable'
	 which equals disable_delete_obsole_file_

Test Plan: make all check

Reviewers: sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22119
2014-08-26 16:26:29 -07:00
Torrie Fischer 0db6b028e7 Update timeout to 50ms instead of 3. 2014-08-26 09:38:45 -07:00
Lei Jin 384400128f move block based table related options BlockBasedTableOptions
Summary:
I will move compression related options in a separate diff since this
diff is already pretty lengthy.
I guess I will also need to change JNI accordingly :(

Test Plan: make all check

Reviewers: yhchiang, igor, sdong

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21915
2014-08-25 14:22:05 -07:00
Yueh-Hsuan Chiang 63a2215c63 Improve Options sanitization and add MmapReadRequired() to TableFactory
Summary:
Currently, PlainTable must use mmap_reads.  When PlainTable is used but
allow_mmap_reads is not set, rocksdb will fail in flush.

This diff improve Options sanitization and add MmapReadRequired() to
TableFactory.

Test Plan:
export ROCKSDB_TESTS=PlainTableOptionsSanitizeTest
make db_test -j32
./db_test

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: you, leveldb

Differential Revision: https://reviews.facebook.net/D21939
2014-08-20 15:53:39 -07:00
sdong 10720a5587 Revert the unintended change that DestroyDB() doesn't clean up info logs.
Summary: A previous change triggered a change by mistake: DestroyDB() will keep info logs under DB directory. Revert the unintended change.

Test Plan: Add a unit test case to verify it.

Reviewers: ljin, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22209
2014-08-20 12:07:32 -07:00
Torrie Fischer 7c5173d27f test: db: fix test to have a smaller timeout for when it runs on faster hardware 2014-08-19 13:45:12 -07:00
sdong 28b5c76004 WriteBatchWithIndex: a wrapper of WriteBatch, with a searchable index
Summary:
Add WriteBatchWithIndex so that a user can query data out of a WriteBatch, to support MongoDB's read-its-own-write.

WriteBatchWithIndex uses a skiplist to store the binary index. The index stores the offset of the entry in the write batch. When searching for a key, the key for the entry is read by read the entry from the write batch from the offset.

Define a new iterator class for querying data out of WriteBatchWithIndex. A user can create an iterator of the write batch for one column family, seek to a key and keep calling Next() to see next entries.

I will add more unit tests if people are OK about this API.

Test Plan:
make all check
Add unit tests.

Reviewers: yhchiang, igor, MarkCallaghan, ljin

Reviewed By: ljin

Subscribers: dhruba, leveldb, xjin

Differential Revision: https://reviews.facebook.net/D21381
2014-08-18 16:37:38 -07:00
sdong 58b0f9d890 Support purging logs from separate log directory
Summary:
1. Support purging info logs from a separate paths from DB path. Refactor the codes of generating info log prefixes so that it can be called when generating new files and scanning log directory.
2. Fix the bug of not scanning multiple DB paths (should only impact multiple DB paths)

Test Plan:
Add unit test for generating and parsing info log files
Add end-to-end test in db_test

Reviewers: yhchiang, ljin

Reviewed By: ljin

Subscribers: leveldb, igor, dhruba

Differential Revision: https://reviews.facebook.net/D21801
2014-08-14 13:22:50 -07:00
Yueh-Hsuan Chiang 1562653ba0 Fixed a signed-unsigned comparison error in db_test
Summary:
Fixed a signed-unsigned comparison error in db_test

Test Plan:
make db_test
2014-08-12 17:26:47 -07:00
Stanislau Hlebik 06a52bda64 Flush only one column family
Summary:
Currently DBImpl::Flush() triggers flushes in all column families.
Instead we need to trigger just the column family specified.

Test Plan: make all check

Reviewers: igor, ljin, yhchiang, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20841
2014-08-11 22:10:32 -07:00
Stanislau Hlebik 7c88249f51 Fix db_test and DBIter
Summary: Fix old issue with DBTest.Randomized with BlockBasedTableWithWholeKeyHashIndex + added printing in DBTest.Randomized.

Test Plan: make all check

Reviewers: zagfox, igor, ljin, yhchiang, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21003
2014-08-08 09:44:14 -07:00
sdong 1242bfcad7 Add DB property "rocksdb.estimate-table-readers-mem"
Summary:
Add a DB Property "rocksdb.estimate-table-readers-mem" to return estimated memory usage by all loaded table readers, other than allocated from block cache.

Refactor the property codes to allow getting property from a version, with DB mutex not acquired.

Test Plan: Add several checks of this new property in existing codes for various cases.

Reviewers: yhchiang, ljin

Reviewed By: ljin

Subscribers: xjin, igor, leveldb

Differential Revision: https://reviews.facebook.net/D20733
2014-08-06 11:39:46 -07:00
Yueh-Hsuan Chiang 1903aa5cc7 Fixed a warning / error in signed and unsigned comparison
Summary:
Fixed the following compilation error detected in mac:
db/db_test.cc:2524:3: note: in instantiation of function template
  specialization 'rocksdb::test::Tester::IsEq<unsigned long long, int>' requested here
    ASSERT_EQ(int_num, 0);
      ^

Test Plan:
make
2014-07-31 14:48:00 -07:00
sdong f04356e660 Add DB::GetIntProperty() to return integer properties to be returned as integers
Summary: We have quite some properties that are integers and we are adding more. Add a function to directly return them as an integer, instead of a string

Test Plan: Add several unit test checks

Reviewers: yhchiang, igor, dhruba, haobo, ljin

Reviewed By: ljin

Subscribers: yoshinorim, leveldb

Differential Revision: https://reviews.facebook.net/D20637
2014-07-28 16:55:57 -07:00
sdong f6784766db Add DB property estimated number of keys
Summary: Add a DB property of estimated number of live keys, by adding number of entries of all mem tables and all files, subtracted by all deletions in all files.

Test Plan: Add the case in unit tests

Reviewers: hobbymanyp, ljin

Reviewed By: ljin

Subscribers: MarkCallaghan, yoshinorim, leveldb, igor, dhruba

Differential Revision: https://reviews.facebook.net/D20631
2014-07-28 15:27:58 -07:00
Lei Jin d650612c4c expose RateLimiter definition
Summary:
User gets undefinied error since the definition is not exposed.
Also re-enable the db test with only upper bound check

Test Plan: db_test, rate_limit_test

Reviewers: igor, yhchiang, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20403
2014-07-25 15:17:06 -07:00
sdong f6b7e1ed1a Allow user to specify DB path of output file of manual compaction
Summary: Add a parameter path_id to DB::CompactRange(), to indicate where the output file should be placed to.

Test Plan: add a unit test

Reviewers: yhchiang, ljin

Reviewed By: ljin

Subscribers: xjin, igor, dhruba, MarkCallaghan, leveldb

Differential Revision: https://reviews.facebook.net/D20085
2014-07-21 19:06:00 -07:00
Stanislau Hlebik 1c9f190ae3 Fix db_test
Summary: Added deletion of DBIterators in DBIterator's tests

Test Plan: make valgrind_check

Reviewers: igor, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D20043
2014-07-16 14:51:43 -07:00
Stanislau Hlebik d916593ead Add Prev() for merge operator
Summary: Implement Prev() with merge operator for DBIterator. Request from mongoDB. Task 4673663.

Test Plan: make all check

Reviewers: sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19743
2014-07-15 16:10:18 -07:00
sdong 0abaed2e08 Support multiple DB directories in universal compaction style
Summary:
This patch adds a target size parameter in options.db_paths and universal compaction will base it to determine which DB path to place a new file.
Level-style stays the same.

Test Plan: Add new unit tests

Reviewers: ljin, yhchiang

Reviewed By: yhchiang

Subscribers: MarkCallaghan, dhruba, igor, leveldb

Differential Revision: https://reviews.facebook.net/D19869
2014-07-15 12:06:28 -07:00
Tomislav Novak 3b97ee96c4 ForwardIterator seek bugfix
Summary:
If `NeedToSeekImmutable()` returns false, `SeekInternal()` won't reset the
contents of `immutable_min_heap_`. However, since it calls `UpdateCurrent()`
unconditionally, if `current_` is one of immutable iterators (previously popped
from `immutable_min_heap_`), `UpdateCurrent()` will overwrite it. As a result,
if old `current_` in fact pointed to the smallest entry, forward iterator will
skip some records.

Fix implemented in this diff pushes `current_` back to `immutable_min_heap_`
before calling `UpdateCurrent()`.

Test Plan:
New unit test (courtesy of @lovro):
   $ ROCKSDB_TESTS=TailingIteratorSeekToSame ./db_test

Reviewers: igor, dhruba, haobo, ljin

Reviewed By: ljin

Subscribers: lovro, leveldb

Differential Revision: https://reviews.facebook.net/D19653
2014-07-10 16:46:13 -07:00
Tomislav Novak 105c1e099b ForwardIterator::status() checks all child iterators
Summary:
Forward iterator only checked `status_` and `mutable_iter_->status()`, which is
not sufficient. For example, when reading exclusively from cache
(kBlockCacheTier), `mutable_iter_->status()` may return kOk (e.g. there's
nothing in the memtable), but one of immutable iterators could be in
kIncomplete. In this case, `ForwardIterator::status()` ought to return that
status instead of kOk.

This diff changes `status()` to also check `imm_iters_`, `l0_iters_`, and
`level_iters_`.

Test Plan:
  ROCKSDB_TESTS=TailingIteratorIncomplete ./db_test

Reviewers: ljin, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D19581
2014-07-10 12:43:12 -07:00
sdong 36de0e5359 Add a function to return current perf level
Summary: Add a function to return the perf level. It is to allow a wrapper of DB to increase the perf level and restore the original perf level after finishing the function call.

Test Plan: Add a verification in db_test

Reviewers: yhchiang, igor, ljin

Reviewed By: ljin

Subscribers: xjin, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D19551
2014-07-10 11:35:48 -07:00
Lei Jin 8a7d1fe616 disable rate limiter test
Summary:
The test is not stable because it relies on disk and only runs for a
short period of time. So misisng a compaction/flush would greatly affect
the rate. I am disabling it for now. What do you guys think?

Test Plan: make

Reviewers: yhchiang, igor, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19599
2014-07-09 22:46:15 -07:00
Lei Jin 73d7147096 make rate limiter test more reliable
Summary:
Randomize keys so that compaction actually happens.
Change the config so that compaction happens more aggressively.
The test takes longer time, but the results are more stable shown by
iostat

Test Plan: ran it

Reviewers: igor, yhchiang

Reviewed By: yhchiang

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19533
2014-07-08 15:15:00 -07:00
Lei Jin 534357ca3a integrate rate limiter into rocksdb
Summary:
Add option and plugin rate limiter for PosixWritableFile. The rate
limiter only applies to flush and compaction. WAL and MANIFEST are
excluded from this enforcement.

Test Plan: db_test

Reviewers: igor, yhchiang, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19425
2014-07-08 12:31:49 -07:00
Yueh-Hsuan Chiang 7b85c1e900 Improve SimpleWriteTimeoutTest to avoid false alarm.
Summary:
SimpleWriteTimeoutTest has two parts: 1) insert two large key/values
to make memtable full and expect both of them are successful; 2) insert
another key / value and expect it to be timed-out.  Previously we also
set a timeout in the first step, but this might sometimes cause
false alarm.

This diff makes the first two writes run without timeout setting.

Test Plan:
export ROCKSDB_TESTS=Time
make db_test

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19461
2014-07-04 00:02:12 -07:00
Yueh-Hsuan Chiang d4d338de33 Add timeout_hint_us to WriteOptions and introduce Status::TimeOut.
Summary:
This diff adds timeout_hint_us to WriteOptions.  If it's non-zero, then
1) writes associated with this options MAY be aborted when it has been
  waiting for longer than the specified time.  If an abortion happens,
  associated writes will return Status::TimeOut.
2) the stall time of the associated write caused by flush or compaction
  will be limited by timeout_hint_us.

The default value of timeout_hint_us is 0 (i.e., OFF.)

The statistics of timeout writes will be recorded in WRITE_TIMEDOUT.

Test Plan:
export ROCKSDB_TESTS=WriteTimeoutAndDelayTest
make db_test
./db_test

Reviewers: igor, ljin, haobo, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D18837
2014-07-03 15:47:02 -07:00
sdong 2459f7ec4e Support Multiple DB paths (without having an interface to expose to users)
Summary:
In this patch, we allow RocksDB to support multiple DB paths internally.
No user interface is supported yet so this patch is silent to users.

Test Plan: make all check

Reviewers: igor, haobo, ljin, yhchiang

Reviewed By: yhchiang

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D18921
2014-07-02 21:14:44 -07:00
sdong 1d05006740 Re-commit the correct part (WalDir) of the revision:
Commit 6634844dba by sdong
Two small fixes in db_test

Summary:
Two fixes:
(1) WalDir to pick a directory under TmpDir to allow two tests running in parallel without impacting each other
(2) kBlockBasedTableWithWholeKeyHashIndex is disabled by mistake (I assume). Enable it.

Test Plan: ./db_test

Reviewers: yhchiang, ljin

Reviewed By: ljin

Subscribers: nkg-, igor, dhruba, haobo, leveldb

Differential Revision: https://reviews.facebook.net/D19389
2014-07-01 18:54:50 -07:00
sdong 30b20604db Revert "Two small fixes in db_test"
This reverts commit 6634844dba.
2014-07-01 17:41:38 -07:00
sdong 9c332aa11a HashLinkList memtable switches a bucket to a skip list to reduce performance outliers
Summary:
In this patch, we enhance HashLinkList memtable to reduce performance outliers when a bucket contains too many entries. We switch to skip list for this case to enable binary search.

Add threshold_use_skiplist parameter to determine when a bucket needs to switch to skip list.

The new data structure is documented in comments in the codes.

Test Plan:
make all check
set threshold_use_skiplist in several tests

Reviewers: yhchiang, haobo, ljin

Reviewed By: yhchiang, ljin

Subscribers: nkg-, xjin, dhruba, yhchiang, leveldb

Differential Revision: https://reviews.facebook.net/D19299
2014-07-01 17:14:15 -07:00
sdong 6634844dba Two small fixes in db_test
Summary:
Two fixes:
(1) WalDir to pick a directory under TmpDir to allow two tests running in parallel without impacting each other
(2) kBlockBasedTableWithWholeKeyHashIndex is disabled by mistake (I assume). Enable it.

Test Plan: ./db_test

Reviewers: yhchiang, ljin

Reviewed By: ljin

Subscribers: nkg-, igor, dhruba, haobo, leveldb

Differential Revision: https://reviews.facebook.net/D19389
2014-07-01 16:58:03 -07:00
Feng Zhu 5656367416 use arena to allocate memtable's bloomfilter and hashskiplist's buckets_
Summary:
    Bloomfilter and hashskiplist's buckets_ allocated by memtable's arena
    DynamicBloom: pass arena via constructor, allocate space in SetTotalBits
    HashSkipListRep: allocate space of buckets_ using arena.
       do not delete it in deconstructor because arena would take care of it.
    Several test files are changed.

Test Plan:
    make all check

Reviewers: ljin, haobo, yhchiang, sdong

Reviewed By: sdong

Subscribers: igor, dhruba

Differential Revision: https://reviews.facebook.net/D19335
2014-06-30 15:54:31 -07:00
Yueh-Hsuan Chiang e813f5b6d9 Allow compaction to reclaim storage more effectively.
Summary:
This diff allows compaction to reclaim storage more effectively.
In the current design, compactions are mainly triggered based on
the file sizes.  However, since deletion entries does not have
value, files which have many deletion entries are less likely
to be compacted.  As a result, it may took a while to make
deletion entries to be compacted.

This diff address issue by compensating the size of deletion
entries during compaction process: the size of each deletion
entry in the compaction process is augmented by 2x average
value size.  The diff applies to both leveled and universal
compacitons.

Test Plan:
develop CompactionDeletionTrigger
make db_test
./db_test

Reviewers: haobo, igor, ljin, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19029
2014-06-24 16:37:06 -06:00
Igor Canadi d4a8423334 Remove seek compaction
Summary:
As discussed in our internal group, we don't get much use of seek compaction at the moment, while it's making code more complicated and slower in some cases.

This diff removes seek compaction and (hopefully) all code that was introduced to support seek compaction.

There is one test case that relied on didIO information. I'll try to find another way to implement it.

Test Plan: make check

Reviewers: sdong, haobo, yhchiang, ljin, dhruba

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19161
2014-06-20 10:23:02 +02:00
Haobo Xu 7a9dd5f214 [RocksDB] Make block based table hash index more adaptive
Summary: Currently, RocksDB returns error if a db written with prefix hash index, is later opened without providing a prefix extractor. This is uncessarily harsh. Without a prefix extractor, we could always fallback to the normal binary index.

Test Plan: unit test, also manually veried LOG that fallback did occur.

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19191
2014-06-19 16:40:32 -07:00
Lei Jin 77db08f27b fix forward iterator bug
Summary: obvious

Test Plan: db_test

Reviewers: sdong, haobo, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D18987
2014-06-10 09:57:26 -07:00
Igor Canadi 6de6a06631 FIFO compaction style
Summary:
Introducing new compaction style -- FIFO.

FIFO compaction style has write amplification of 1 (+1 for WAL) and it deletes the oldest files when the total DB size exceeds pre-configured values.

FIFO compaction style is suited for storing high-frequency event logs.

Test Plan: Added a unit test

Reviewers: dhruba, haobo, sdong

Reviewed By: dhruba

Subscribers: alberts, leveldb

Differential Revision: https://reviews.facebook.net/D18765
2014-05-21 11:43:35 -07:00
sdong 3e4a9ec241 Arena to inline 2KB of data in it.
Summary:
In order to use arena to a use case that the total allocation size might be small (LogBuffer is already such a case), inline 1KB of data in it, so that it can be mostly in stack or inline in another class.

If always inlining 2KB is a concern, I could make it a template to determine what to inline. However, dependents need to changes. Doesn't go with it for now

Test Plan: make all check.

Reviewers: haobo, igor, yhchiang, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18609
2014-05-14 11:49:01 -07:00
Yueh-Hsuan Chiang 1c7799d8aa Fixed a file-not-found issue when a log file is moved to archive.
Summary:
Fixed a file-not-found issue when a log file is moved to archive
by doing a missing retry.

Test Plan:
make db_test
export ROCKSDB_TEST=TransactionLogIteratorRace
./db_test

Reviewers: sdong, haobo

Reviewed By: sdong

CC: igor, leveldb

Differential Revision: https://reviews.facebook.net/D18669
2014-05-12 17:50:21 -07:00
Igor Canadi 8e37a29bfb Compaction with zero outputs
Summary: We had a hypothesis in https://reviews.facebook.net/D18507 that empty-string internal keys might have been caused by compaction filter deleting all the entries. I added a unit test for that case. Unforutnately, everything works as expected.

Test Plan: this is a test

Reviewers: dhruba, haobo, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18519
2014-05-08 13:48:39 -07:00
Igor Canadi d2569fea47 log_and_apply_bench on a new benchmark framework
Summary:
db_test includes Benchmark for LogAndApply. This diff removes it from db_test and puts it into a separate log_and_apply bench. I just wanted to play around with our new benchmark framework and figure out how it works.

I would also like to show you how great it is! I believe right set of microbenchmarks can speed up our productivity a lot and help catch early regressions.

Test Plan: no

Reviewers: dhruba, haobo, sdong, ljin, yhchiang

Reviewed By: yhchiang

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18261
2014-05-05 11:11:48 -07:00
sdong 4a7c747064 Revert "Revert "Allow allocating dynamic bloom, plain table indexes and hash linked list from huge page TLB""
And make the default 0 for hash linked list memtable

This reverts commit d69dc64be7.
2014-05-04 13:56:29 -07:00
Igor Canadi d69dc64be7 Revert "Allow allocating dynamic bloom, plain table indexes and hash linked list from huge page TLB"
This reverts commit 7dafa3a1d7.
2014-05-04 08:37:09 -07:00
Igor Canadi 0afc8bc29a xxHash
Summary:
Originally: https://github.com/facebook/rocksdb/pull/87/files

I'm taking over to apply some finishing touches

Test Plan: will add tests

Reviewers: dhruba, haobo, sdong, yhchiang, ljin

Reviewed By: yhchiang

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18315
2014-05-01 14:09:32 -04:00
sdong 7dafa3a1d7 Allow allocating dynamic bloom, plain table indexes and hash linked list from huge page TLB
Summary: Add an option to allocate a piece of memory from huge page TLB. Add options to trigger it in dynamic bloom, plain table indexes andhash linked list hash table.

Test Plan: make all check

Reviewers: haobo, ljin

Reviewed By: haobo

CC: nkg-, dhruba, leveldb, igor, yhchiang

Differential Revision: https://reviews.facebook.net/D18357
2014-04-30 11:02:26 -07:00
Yueh-Hsuan Chiang 9d9d2965cb Add a new mem-table representation based on cuckoo hash.
Summary:
= Major Changes =
* Add a new mem-table representation, HashCuckooRep, which is based cuckoo hash.
  Cuckoo hash uses multiple hash functions.  This allows each key to have multiple
  possible locations in the mem-table.

  - Put: When insert a key, it will try to find whether one of its possible
    locations is vacant and store the key.  If none of its possible
    locations are available, then it will kick out a victim key and
    store at that location.  The kicked-out victim key will then be
    stored at a vacant space of its possible locations or kick-out
    another victim.  In this diff, the kick-out path (known as
    cuckoo-path) is found using BFS, which guarantees to be the shortest.

 - Get: Simply tries all possible locations of a key --- this guarantees
   worst-case constant time complexity.

 - Time complexity: O(1) for Get, and average O(1) for Put if the
   fullness of the mem-table is below 80%.

 - Default using two hash functions, the number of hash functions used
   by the cuckoo-hash may dynamically increase if it fails to find a
   short-enough kick-out path.

 - Currently, HashCuckooRep does not support iteration and snapshots,
   as our current main purpose of this is to optimize point access.

= Minor Changes =
* Add IsSnapshotSupported() to DB to indicate whether the current DB
  supports snapshots.  If it returns false, then DB::GetSnapshot() will
  always return nullptr.

Test Plan:
Run existing tests.  Will develop a test specifically for cuckoo hash in
the next diff.

Reviewers: sdong, haobo

Reviewed By: sdong

CC: leveldb, dhruba, igor

Differential Revision: https://reviews.facebook.net/D16155
2014-04-29 17:13:46 -07:00