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https://github.com/kentnl/chi-driver-lmdb

use OpenLDAPs LMDB Key-Value store as a cache backend
https://github.com/kentnl/chi-driver-lmdb

perl

Last synced: 26 days ago
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use OpenLDAPs LMDB Key-Value store as a cache backend

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README 

        
# NAME



CHI::Driver::LMDB - use OpenLDAPs LMDB Key-Value store as a cache backend.



# VERSION



version 0.002005



# SYNOPSIS



    use CHI;



    my $cache = CHI->new(

      driver => 'LMDB',

      root_dir => 'some/path',

      namespace => "My::Project",

    );



See [`CHI` documentation](https://metacpan.org/pod/CHI) for more details on usage.



# ATTRIBUTES



## `dir_create_mode`



What mode (if any) to use when creating `root_dir` if it does not exist.



    ->new(

      # Default is 775 = rwxr-xr-x

      dir_create_mode => oct 666,

    );



## `root_dir`



The prefix directory the `LMDB` data store will be installed to.



    ->new(

      root_dir => 'some/path'

    )



Default is:



    OSTEMPDIR/chi-driver-lmdb-$EUID



## `cache_size`



The size in bytes for each database.



This is a convenience wrapper for ["mapsize"](#mapsize) which supports suffixes:



    cache_size => 5  # 5 bytes

    cache_size => 5k # 5 Kilobytes

    cache_size => 5m # 5 Megabytes ( default )



This is also designed for syntax compatibility with [`CHI::Driver::FastMmap`](https://metacpan.org/pod/CHI::Driver::FastMmap)



## `single_txn`



    single_txn => 1



**SPEED**: For performance benefits, have a single transaction

that lives from the creation of the CHI cache till its destruction.



However, **WARNING:** this flag is currently a bit dodgy, and CHI caches being kept alive

till global destruction **WILL** trigger a `SEGV`, and potentially leave your cache broken.



You can avoid this by manually destroying the cache with:



    undef $cache



Prior to global destruction.



## `db_flags`



Flags to pass to `OpenDB`/`LMDB_File->open`.



See [`LMDB_File`'s constructor options](https://metacpan.org/pod/LMDB_File#LMDB_File) for details.



    use LMDB_File qw( MDB_CREATE );



    db_flags => MDB_CREATE # default



## `tx_flags`



Flags to pass to `LMDB::Env->new`



See [`LMDB::Env`'s constructor options](https://metacpan.org/pod/LMDB_File#LMDB::Env) for details.



Default is `0`



    tx_flags => 0 # no flags



## `put_flags`



Flags to pass to `->put(k,v,WRITE_FLAGS)`.



See [LMDB\_File->put options](https://metacpan.org/pod/LMDB_File#LMDB_File) for details.



## `mapsize`



Passes through to `LMDB::Env->new( mapsize => ... )`



Default value is taken from ["cache\_size"](#cache_size) with some `m/k` math if its set.



## `maxreaders`



Passes through to `LMDB::Env->new( maxreaders => ... )`



## `maxdbs`



Passes through to `LMDB::Env->new( maxdbs => ... )`



Defines how many CHI namespaces ( Databases ) a path can contain.



Default is 1024.



## `mode`



Passes through to `LMDB::Env->new( mode => ... )`



Defines the permissions on created DB Objects.



Defaults to `oct 600` == `-rw-------`



## `flags`



Passes through to `LMDB::Env->new( flags => ... )`



# PERFORMANCE



If write performance is a little slow for you ( due to the defaults being a single

transaction per SET/GET operation, and transactions being flushed to disk when written ),

there are two ways you can make performance a little speedy.



## Single Transaction Mode.



If you pass `single_txn => 1` the cache will be given a single transaction

for the life of its existence. However, pay attention to the warnings about cleaning

up properly in ["single\_txn"](#single_txn).



Also, this mode is less ideal if you want to have two processes sharing a cache,

because the data won't be visible on the other one till it exits! ☺



## `NOSYNC` Mode.



You can also tell LMDB **NOT** to call `sync` at the end of every transaction,

and this will greatly improve write performance due to IO being greatly delayed.



This greatly weakens the databases consistency, but that seems like a respectable

compromise for a mere cache backend, where a missing record is a performance hit, not a loss of data.



    use LMDB_File qw( MDB_NOSYNC MDB_NOMETASYNC );

    ...

    my $cache = CHI->new(

      ...

      flags => MDB_NOSYNC | MDB_NOMETASYNC

    );



This for me cuts down an operation that takes 30 seconds worth of writes down to 6 ☺.



# In Depth



For an in-depth comparison of the performance of various options,

and how that compares to [`CHI::Driver::FastMmap`](https://metacpan.org/pod/CHI::Driver::FastMmap),

see [http://kentnl.github.io/CHI-Driver-LMDB](http://kentnl.github.io/CHI-Driver-LMDB)



# AUTHOR



Kent Fredric 



# COPYRIGHT AND LICENSE



This software is copyright (c) 2017 by Kent Fredric .



This is free software; you can redistribute it and/or modify it under

the same terms as the Perl 5 programming language system itself.