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Gregory Burd
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README.md
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README.md
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EMDB
====
EMDB is a NIF library for the [Memory-Mapped Database](http://highlandsun.com/hyc/mdb/) database, aka. MDB.
The main purpose of this package is to provide a **very fast** Riak [backend](http://wiki.basho.com/Storage-Backends.html).
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EMDB
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====
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But this module could also be used as a general key-value store to replace:
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EMDB is a NIF library for the [Memory-Mapped Database](http://highlandsun.com/hyc/mdb/) database, aka. MDB.
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* [DETS](http://www.erlang.org/doc/man/dets.html)
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* TokyoCabinet: [TCERL](http://code.google.com/p/tcerl/)
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* [QDBM](http://fallabs.com/qdbm/)
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* [Bitcask](https://github.com/basho/bitcask)
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* [eLevelDB](https://github.com/basho/eleveldb)
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* [BerkleyDB](http://www.oracle.com/technetwork/products/berkeleydb/overview/index.html)
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* ...
Requirements
------------
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* Erlang R14B04+
* GCC 4.2+ or MS VisualStudio 2010+
Build
-----
$ make
API
---
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The following functions were implemented:
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The main purpose of this package is to provide an Erlang API for this excellent BTREE implementation. Secondly to build an alternative Riak/KV [backend](http://wiki.basho.com/Storage-Backends.html) and Riak's AAE feature based on this. Finally it'd be nice to build an ETS-compatible API (ala "lets" for LevelDB) to ease adoption in other places where DETS is just not up to the task.
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Requirements
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------------
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* Erlang R14B04+
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* GCC 4.2+ or MS VisualStudio 2010+
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Build
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-----
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$ make
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API
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---
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The following functions were implemented:
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* `open/1`: equivalent to `emdb:open(DirName, 10485760)`.
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* `open/2`: equivalent to `emdb:open(DirName, 10485760, 0)`.
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* `put/2`: inserts Key with value Val into the database. Assumes that the key is not present, 'key_exit' is returned otherwise.
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* `get/1`: retrieves the value stored with Key in the database.
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* `del/1`: Removes the key-value with key Key from database.
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* `update/2`: inserts Key with value Val into the database if the key is not present, otherwise updates Key to value Val.
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* `update/2` or `upd/2`: inserts Key with value Val into the database if the key is not present, otherwise updates Key to value Val.
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* `drop/1`: deletes all key-value pairs in the database.
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Usage
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-----
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```
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$ make
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$ ./start.sh
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%% create a new database
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@ -82,32 +92,32 @@ $ ./start.sh
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...
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17> q().
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```
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#### Note:
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The code below creates a new database with **80GB** MapSize, **avoid fsync**
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after each commit (for max speed) and use the experimental **MDB_FIXEDMAP**.
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The code below creates a new database with **80GB** MapSize, **avoids fsync** after each commit (for an "ACI" but not "D" database we trade durability for speed) and uses the experimental **MDB_FIXEDMAP**.
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```
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{ok, Handle} = emdb:open("/tmp/emdb2", 85899345920, ?MDB_NOSYNC bor ?MDB_FIXEDMAP).
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```
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Performance
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-----------
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For maximum speed, this library use only binaries for both keys and values.
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See the impressive [microbench](http://highlandsun.com/hyc/mdb/microbench/) against:
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See the [microbench](http://highlandsun.com/hyc/mdb/microbench/) against:
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* Google's LevelDB (which is slower and can stall unlike Basho's fork of LevelDB)
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* SQLite3
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* Kyoto TreeDB
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* BerkeleyDB 5.x
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MDB performs better on 64-bit arch.
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MDB performs mmap's the database, so unless your dataset is < 2^32 bytes you'll
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need to run on a 64-bit arch system.
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Supported Operating Systems
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--------------
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Should work on 32/64-bit architectures:
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Should work on:
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* Linux
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* OSX
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@ -124,13 +134,24 @@ TODO
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* basho_bench driver
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* EQC, PULSE testing
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* Key expirey
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* Atomic group commit (for 2i)
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Volunteers are always welcome!
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* renaming
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* emdb -> lmdb
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* emdb.c -> lmdb_nif.c
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* improve stats
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* txn API
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* cursor API
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* config
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* use async_nif affinity
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* riak_kv backend
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* use dups
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* 2i
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* aae alternative
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Status
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------
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Work in progress, not production quality and not supported by Basho Technologies.
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LICENSE
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-------
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