Next steps:
[] Merge the schema change patch: https://gerrit.wikimedia.org/r/#/q/If5c137f6
[] Deploy the schema change to all wikis: //(task not filed yet)//
[] Merge the "populate field" patch: https://gerrit.wikimedia.org/r/#/q/I971edf01
[] Wait for the "populate field" patch to be deployed to all wikis.
[] (optional) Schema change to drop the default on the `el_index_60` column: //(task not filed yet)//
[] Run maintenance/populateExternallinksIndex60.php: //(task not filed yet)//
[] Merge the "start using field" patch: https://gerrit.wikimedia.org/r/#/q/I84d224ef
[] Announce in tech news that Special:LinkSearch results might be incomplete in between when the above patch is deployed to the wiki and the maintenance script below is run on the wiki.
[] Run maintenance/refreshExternallinksIndex.php: //(task not filed yet)//
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Crazy limit offsets like this are showing up in slow query logs for enwiki:
SELECT /* ApiQueryExtLinksUsage::run */ page_id,page_namespace,page_title,el_to FROM `page`,`externallinks` WHERE (page_id=el_from) AND (el_index LIKE 'http://gov.nih.nlm.ncbi.%' ) LIMIT 768500,501;
By itself it's not too bad, < 10 seconds, but they're appearing in spikes presumably from something automated and causing concurrency issues.
Suggest disallowing such page offsets or redesigning the pagination method.
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**Version**: 1.23.0
**Severity**: major