MariaDB starting with 10.1.0

InnoDB/XtraDB Page Compression was added in MariaDB 10.1.0

Overview

Page compression is alternative way to compress you tables. In page compression, only uncompressed pages are stored on buffer pool. This approach differs significantly from legacy InnoDB compressed tables using row_format=compressed, where both uncompressed and compressed pages can be in buffer pool. In page compression, page is actually compressed just before page is written to filespace. Similarly, page is uncompressed when it is read from tablespace before it is placed on buffer pool. Additionally, page compression supports different compression algorithms, not only zlib. For the moment, the only engines that fully support page compression are XtraDB and InnoDB. Page compression is available only if innodb-file-format=Barracuda and innodb-file-per-table=1.

Page compression can be used on any file system but most beneficial it is on SSDs and Non-Volatile Memory (NVM) devices like FusionIO atomic-series http://www.fusionio.com/products/atomic-series/. Page compression design works also with double-write enabled, but for best performance is reached if double-write is disabled (i.e. innodb-doublewrite=0) and atomic writes are enabled (innodb-use-atomic-writes=1). This naturally requires that used file system and storage device supports atomic writes (https://blog.mariadb.org/mariadb-introduces-atomic-writes/).

Choosing compression algorithm

You specify which compression method to use with the --innodb-compression-algorithm= startup option for MariaDB. The options are:

OptionDescription
noneDefault. Data is not compressed.
zlibPages are compressed with bundled zlib compression method.
lz4Pages are compressed using https://code.google.com/p/lz4/ compression method.
lzoPages are compressed using http://www.oberhumer.com/opensource/lzo/ compression method.
lzmaPages are compressed using http://tukaani.org/xz/ compression method.
bzip2Pages are compressed using http://www.bzip.org/ compression method.
snappyPages are compressed using https://code.google.com/p/snappy/.
MariaDB starting with 10.1.3

Support for snappy compression method was added in MariaDB 10.1.3

Because all of these compression methods are not available by default on all distributions and MariaDB server does not bundle them, you may need to download the desired compression method package from the above links, install the package and finally recompile MariaDB server from the source distribution with:

cmake .
make
make install

After the first command above, please check that cmake has found the desired compression method from your system.

The compression method can be changed whenever needed. Currently the compression method is global (i.e. you can't specify compression method/table).

set global innodb_compression_method=lz4;

From this point on page compressed tables will use the lz4 compression method. This setting does not change already compressed pages that were compressed with a different compression method. This is because MariaDB supports pages that are uncompressed, compressed with e.g. lzo and compressed with e.g. lz4 in same tablespace. This is possible because every page on InnoDB tablespace contains compression method information on page header metadata.

Choosing compression level

You specify the default compression level to use with the --innodb-compression-level= startup option for MariaDB. Values are 0-9. Note that not all compression methods allow choosing the compression level and in those cases the compression level value is ignored.

Creating compressed tables

Only tables that are specified to be compressed are actually compressed,. You can create a page compressed table with:

create table users(user_id int not null, b name varchar(200), primary key(user_id)) 
  engine=innodb page_compressed=1;

Persistent TRIM

Normally InnoDB always writes the full page i.e. by default 16K (innodb-page-size). However, when compression is used you may use a different approach. On file systems that support fallocate() and creating sparse files (e.g. ext3/4, xfs, nvmfs, etc) by using FALLOC_FL_PUNCH_HOLE, InnoDB will only write the actual compressed page size aligned to sector size. The rest of the page is trimmed using fallocate(file_handle, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, file_offset, remainder_len);. This is needed because InnoDB always reads the full page size (default 16K).

This feature can be configured by using innodb_use_trim and innodb_use_fallocate:

innodb_use_trim=ON
innodb_use_fallocate=ON

Multi-threaded flush

Normally MariaDB uses a single thread to flush dirty pages out of the buffer pool. However, when compression is used and the system has multiple-cores/CPUs and a fast I/O device (like an NVM device), you may benefit by using the multi-threaded flush mechanism. This feature has two configuration variables at startup time:

--innodb-use-mtflush= startup option for MariaDB to enable multi-threaded flush. By default this is 8. You may configure the number of used threads by --innodb-mtflush-threads. The maximum is currently 64. In multi-core systems a value similar to innodb-buffer-pool-instances that is close to the number of cores have shown to be effective. Naturally, you should benchmark the suitable value using your own application as a workload.

Monitoring compression

SHOW STATUS contains new status variables that can be used to monitor compression

Status variable nameValuesDescription
Innodb_page_compression_saved0Bytes saved by compression
Innodb_page_compression_trim_sect5120Number of 512 sectors trimmed
Innodb_page_compression_trim_sect10240Number of 1024 sectors trimmed
Innodb_page_compression_trim_sect20480Number of 2048 sectors trimmed
Innodb_page_compression_trim_sect40960Number of 4096 sectors trimmed
Innodb_page_compression_trim_sect81920Number of 8192 sectors trimmed
Innodb_page_compression_trim_sect163840Number of 16384 sectors trimmed
Innodb_page_compression_trim_sect327680Number of 32768 sectors trimmed
Innodb_num_pages_page_compressed0Number of pages compressed
Innodb_num_page_compressed_trim_op0Number of trim operations
Innodb_num_page_compressed_trim_op_saved0Number of trim operations saved
Innodb_num_pages_page_decompressed0Number of pages decompressed
Innodb_num_pages_page_compression_error0Number of compression errors
Innodb_have_lz4ONDoes system have lz4 compression method available
Innodb_have_lzoONDoes system have lzo compression method available
Innodb_have_lzmaONDoes system have lzma compression method available
Innodb_have_bzip2ONDoes system have bzip2 compression method available
Innodb_have_snappyONDoes system have snappy compression method available

Thanks

  • Table compression was developed with cooperation by Fusion-io http://fusionio.com and especially Dhananjoy Das and Torben Mathiasen.

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