Direct I/O Improvements (UNIX)
Performance improvements were made to Ingres direct I/O capability in UNIX environments, including Linux.
Control of direct I/O is now configured at the system rather than DBMS level. Administrators can select direct I/O independently for tables, the transaction log, and build files (tables being loaded). Direct I/O is beneficial in large data warehouse environments, when the OS file system cache is ineffective (because of large sequential scans). OLTP-oriented installations are likely to perform better with direct I/O off.
New direct I/O configuration parameters were added to Ingres:
ii.$.config.direct_io
Enables direct I/O for tables.
Default: OFF
ii.$.config.direct_io_log
Enables direct I/O for the transaction log.
Default: OFF
ii.$.config.direct_io_load
Enables direct I/O when writing bulk-load files for (bulk-load) COPY FROM, CREATE TABLE AS SELECT, MODIFY, and CREATE INDEX. Typically, direct_io_load ON is recommended only in cases where normal mode floods the operating system file cache.
Default: OFF
Note: If the platform or file system does not support direct I/O, the direct I/O parameters are ignored.
The configuration parameters dbms.*.direct_io and recovery.direct_io are now obsolete. During upgrade, if dbms.*.direct_io is ON in the old version, then config.direct_io and config.direct_io_log are set to ON.
You can set the new direct I/O parameters using the iisetres command.