The Ultimate Guide to High Availability with MariaDB

Disk Based Joins

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Joins are performed in-memory on the UM node. When a join operation exceeds the memory allocated on the UM for query joins, the query is aborted with an error code IDB-2003. Disk based joins enable such queries to use disk for intermediate join data in case when the memory needed for join exceeds the memory limit on the UM. All though slower in performance as compared to a fully in-memory join, and bound by the temporary space on disk, it does allow such queries to complete. Disk based joins does not include aggregation and DML joins.

The following variables in HashJoin element in the Calpont.xml configuration file relate to disk based joins. Calpont.xml resides in the etc directory for your installation(/usr/local/mariadb/columnstore/etc).

  • AllowDiskBasedJoin – Option to use disk Based joins. Valid values are Y (enabled) or N (disabled). Default is disabled.
  • TempFileCompression – Option to use compression for disk join files. Valid values are Y (use compressed files) or N (use non-compressed files).
  • TempFilePath – The directory path used for the disk joins. By default, this path is the tmp directory for your installation (i.e., /usr/local/mariadb/columnstore/tmp). Files (named infinidb-join-data*) in this directory will be created and cleaned on an as needed basis. The entire directory is removed and recreated by ExeMgr at startup.)

Note: When using disk based joins, it is strongly recommended that the TempFilePath reside on its own partition as the partition may fill up as queries are executed.

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