Manual:$wgDisableSearchUpdate

From Linux Web Expert

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

Details

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.