When calling UpdateAttributes() to update document attributes in real-time, changes are first written to the in-memory copy of attributes (docinfo must be set to extern). Then, once searchd shuts down normally (via SIGTERM being sent), the changes are written to disk. Introduced in version 0.9.9-rc1.

Starting with 0.9.9-rc1, it is possible to tell searchd to periodically write these changes back to disk, to avoid them being lost. The time between those intervals is set with attr_flush_period, in seconds.

It defaults to 0, which disables the periodic flushing, but flushing will still occur at normal shut-down.

Example:

attr_flush_period = 900 # persist updates to disk every 15 minutes