Manual:$wgDisableSearchUpdate

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Search: $wgDisableSearchUpdate
If you've disabled search semi-permanently, this also disables updates to the table.
Introduced in version:pre 1.1.0
Removed in version:still in use
Allowed values:(boolean)
Default value:false

Details[edit]

If you've disabled search semi-permanently, this also disables updates to the table. If you ever re-enable, be sure to rebuild the search table using rebuildtextindex.php .

The searchindex table gets populated when edits are saved. This may slow down your wiki if it gets a high rate of edits. You can disable search updates with this setting, and periodically run updateSearchIndex.php to update it during off-peak hours.