A library that provides an embeddable, persistent key-value store for fast storage.
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Aaron Gao 259a00eaca unbiase readamp bitmap
Summary:
Consider BlockReadAmpBitmap with bytes_per_bit = 32. Suppose bytes [a, b) were used, while bytes [a-32, a)
 and [b+1, b+33) weren't used; more formally, the union of ranges passed to BlockReadAmpBitmap::Mark() contains [a, b) and doesn't intersect with [a-32, a) and [b+1, b+33). Then bits [floor(a/32), ceil(b/32)] will be set, and so the number of useful bytes will be estimated as (ceil(b/32) - floor(a/32)) * 32, which is on average equal to b-a+31.

An extreme example: if we use 1 byte from each block, it'll be counted as 32 bytes from each block.

It's easy to remove this bias by slightly changing the semantics of the bitmap. Currently each bit represents a byte range [i*32, (i+1)*32).

This diff makes each bit represent a single byte: i*32 + X, where X is a random number in [0, 31] generated when bitmap is created. So, e.g., if you read a single byte at random, with probability 31/32 it won't be counted at all, and with probability 1/32 it will be counted as 32 bytes; so, on average it's counted as 1 byte.

*But there is one exception: the last bit will always set with the old way.*

(*) - assuming read_amp_bytes_per_bit = 32.
Closes https://github.com/facebook/rocksdb/pull/2259

Differential Revision: D5035652

Pulled By: lightmark

fbshipit-source-id: bd98b1b9b49fbe61f9e3781d07f624e3cbd92356
2017-05-10 01:49:52 -07:00
arcanist_util Fix arc setting for Facebook internal tools 2017-02-02 13:24:16 -08:00
buckifier internal_repo_rocksdb to build Java and RocksDB LITE 2017-04-12 15:13:41 -07:00
build_tools Set VALGRIND_VER 2017-05-01 16:35:15 -07:00
cache Add GPLv2 as an alternative license. 2017-04-27 18:06:12 -07:00
cmake/modules CMake: more MinGW fixes 2017-04-06 14:09:13 -07:00
coverage Fix coverage script 2014-11-03 14:53:00 -08:00
db unbiase readamp bitmap 2017-05-10 01:49:52 -07:00
docs Add documentation license 2017-04-27 18:06:11 -07:00
env fix memory alignment with logical sector size 2017-05-04 01:30:13 -07:00
examples CMake: more MinGW fixes 2017-04-06 14:09:13 -07:00
hdfs Add GPLv2 as an alternative license. 2017-04-27 18:06:12 -07:00
include/rocksdb Add C API to set max_file_opening_threads option 2017-05-08 22:49:32 -07:00
java Remove orphaned Java classes 2017-05-02 21:13:49 -07:00
memtable Add GPLv2 as an alternative license. 2017-04-27 18:06:12 -07:00
monitoring Add GPLv2 as an alternative license. 2017-04-27 18:06:12 -07:00
options Print compaction_options_universal.stop_style in LOG file 2017-05-09 15:57:44 -07:00
port port: updated PhysicalCoreID() 2017-05-09 19:06:39 -07:00
table unbiase readamp bitmap 2017-05-10 01:49:52 -07:00
third-party Fix build with MinGW 2017-03-30 16:54:52 -07:00
tools Allow IntraL0 compaction in FIFO Compaction 2017-05-04 18:16:13 -07:00
util travis: add Windows cross-compilation 2017-05-05 23:20:01 -07:00
utilities support PopSavePoint for WriteBatch 2017-05-03 10:57:45 -07:00
.clang-format A script that automatically reformat affected lines 2014-01-14 12:21:24 -08:00
.deprecated_arcconfig Update ShipIt to honor TARGETS updates 2017-04-13 16:12:03 -07:00
.gitignore Add buckifier script to github repo 2017-04-04 16:24:26 -07:00
.travis.yml travis: add Windows cross-compilation 2017-05-05 23:20:01 -07:00
appveyor.yml Rework test running script. 2017-04-05 11:39:20 -07:00
AUTHORS Add AUTHORS file. Fix #203 2014-09-29 10:52:18 -07:00
CMakeLists.txt travis: add Windows cross-compilation 2017-05-05 23:20:01 -07:00
CONTRIBUTING.md facebook accounts are not required for CLA signers 2014-07-08 05:57:54 -04:00
COPYING Add GPLv2 as an alternative license. 2017-04-27 18:06:12 -07:00
DEFAULT_OPTIONS_HISTORY.md Change the default of delayed slowdown value to 16MB/s 2017-02-01 20:39:17 -08:00
DUMP_FORMAT.md First version of rocksdb_dump and rocksdb_undump. 2015-06-19 16:24:36 -07:00
HISTORY.md Add bulk create/drop column family API 2017-05-07 23:20:46 -07:00
INSTALL.md AIX and Solaris Sparc Support 2017-04-21 20:48:04 -07:00
LANGUAGE-BINDINGS.md Adding Dlang to the list 2017-02-16 17:24:10 -08:00
LICENSE Updated all copyright headers to the new format. 2016-02-09 15:12:00 -08:00
Makefile Extract statistics tests into separate file 2017-04-26 14:47:23 -07:00
PATENTS Update Patent Grant. 2015-04-13 10:33:43 +01:00
README.md Appveyor badge to show master branch 2016-07-26 13:54:08 -07:00
ROCKSDB_LITE.md Optimistic Transactions 2015-05-29 14:36:35 -07:00
src.mk Extract statistics tests into separate file 2017-04-26 14:47:23 -07:00
TARGETS Extract statistics tests into separate file 2017-04-26 14:47:23 -07:00
thirdparty.inc Introduce XPRESS compresssion on Windows. (#1081) 2016-04-19 22:54:24 -07:00
USERS.md Update USERS.md add user Pika 2017-01-25 10:39:17 -08:00
Vagrantfile Update Vagrant file (test internal phabricator workflow) 2016-10-28 15:39:19 -07:00
WINDOWS_PORT.md Commit both PR and internal code review changes 2015-07-07 16:58:20 -07:00

RocksDB: A Persistent Key-Value Store for Flash and RAM Storage

Build Status Build status

RocksDB is developed and maintained by Facebook Database Engineering Team. It is built on earlier work on LevelDB by Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)

This code is a library that forms the core building block for a fast key value server, especially suited for storing data on flash drives. It has a Log-Structured-Merge-Database (LSM) design with flexible tradeoffs between Write-Amplification-Factor (WAF), Read-Amplification-Factor (RAF) and Space-Amplification-Factor (SAF). It has multi-threaded compactions, making it specially suitable for storing multiple terabytes of data in a single database.

Start with example usage here: https://github.com/facebook/rocksdb/tree/master/examples

See the github wiki for more explanation.

The public interface is in include/. Callers should not include or rely on the details of any other header files in this package. Those internal APIs may be changed without warning.

Design discussions are conducted in https://www.facebook.com/groups/rocksdb.dev/