https://bugzilla.wikimedia.org/show_bug.cgi?id=51254
--- Comment #5 from Sean Pringle <[email protected]> --- Firstly, we've determined this problem occurred due to an (apparent) bug in pt-online-schema-change when using a combination of: - A table without primary key - A table with unique indexes that all include nullable columns - An unfortunately timed REPLACE statement in normal db traffic Posc does online table alteration by: - Creating a copy of the table with altered schema - Setting triggers on the original table to keep the copy updated - Copying data across using a batch process In this case, posc set a DELETE trigger on tag_summary using a poor UNIQUE index (ts_log_id) with low cardinality and a nullable field. Then during the batching process, an external REPLACE statement with ts_log_id=NULL caused many too many rows to be deleted in the temporary table being altered. Given that many rows in tag_summary have ts_log_id=NULL, the table was massively reduced in size. Now to the fix: We've checked the other wikis and found no problems; only enwiki was affected. Furthermore, only enwiki.tag_summary was affected. We've verified that enwiki.change_tag is complete and did not suffer the same problem. This was based on: - Index cardinality and table size information collected before running the schema migration - An investigation of the events in the binary log surrounding the migration period Currently we are rebuilding tag_summary based on change_tag data. That will complete within 30 mins at the time of writing this comment. -- You are receiving this mail because: You are on the CC list for the bug. _______________________________________________ Wikibugs-l mailing list [email protected] https://lists.wikimedia.org/mailman/listinfo/wikibugs-l
