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by evanelias
2230 days ago
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One annoying wrinkle in MySQL's purge implementation: it won't progress to any old row versions that are newer than the oldest transaction, even if there are no transactions that could ever possibly access those rows. [1] As you noted, this can get painful since purge effectively gets blocked -- if you have a high-volume OLTP workload with heavy emphasis on quick small UPDATEs / DELETEs, and then introduce a single very long-running read transaction (such as a logical dump/backup), purge can't make progress. But this is just due to the current implementation. In theory a smarter system could differentiate between row versions actually needed by old transactions vs ones that are inaccessible to all transactions. [1] https://bugs.mysql.com/bug.php?id=74919 |
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