Product Documentation

Database Administrator's Guide

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Defer Backup I/O for Improved Performance

When a dynamic dump runs, the disk read and write operations of the backup process can slow the performance of other database operations. FairCom DB supports an option that allows an administrator to reduce the performance impact of the dynamic dump.

The FairCom DB configuration option:

  • DYNAMIC_DUMP_DEFER <milliseconds>

This option sets a time in milliseconds that the dynamic dump thread will sleep after each write of a 64KB block of data to the dump backup file.

An application developer can also use the c-tree ctSETCFG() API function to set the DYNAMIC_DUMP_DEFER value. For example, the following call specifies a 10-millisecond DYNAMIC_DUMP_DEFER time:

  • ctSETCFG( setcfgDYNAMIC_DUMP_DEFER, "10" );

The DYNAMIC_DUMP_DEFER value set by a call to ctSETCFG() takes effect immediately, so this API call can be used by administrators to adjust the speed of a running dynamic dump depending on the amount of other database activity.

Note: The maximum allowed DYNAMIC_DUMP_DEFER time is 5000 milliseconds, set at compile-time. If a value is specified that exceeds this limit, the DYNAMIC_DUMP_DEFER time is set to DYNAMIC_DUMP_DEFER_MAX.

The FairCom DB Administrator utility, ctadmn, was also updated to support the dump sleep time option to change this value at run time. The "Change Server Settings" menu is available from the main menu of the ctadmn utility.

Defer Interval

The DYNAMIC_DUMP_DEFER option causes the dynamic dump to pause for the specified number of milliseconds each time it writes 64 KB of data to the dynamic dump stream file. For large backups, even the smallest DYNAMIC_DUMP_DEFER value of 1 millisecond adds significant time to the dynamic dump. For example, 100 GB = 1600000 * 1 ms. = 1600 seconds of additional time.

An additional keyword, DYNAMIC_DUMP_DEFER_INTERVAL, specifies the number of 64 KB blocks that are written before the DYNAMIC_DUMP_DEFER sleep is performed. For example, DYNAMIC_DUMP_DEFER_INTERVAL 16 would cause the DYNAMIC_DUMP_DEFER sleep to occur after every 64 KB * 16 = 1 MB of data written to the dump stream file.

Note: If a value greater than 5000 is specified for DYNAMIC_DUMP_DEFER_INTERVAL, the value is set to 5000. If a value less than 1 is specified, the value is set to 1.

This option can be set by the ctSETCFG() API function:


A new menu option to set this value has been added to option 10 of the FairCom DB Server Administration (ctadmn) menu.