# 4783 OPTIMIZE TABLE Does Not Use a Covering Lock While Backing Up/Replacing Table Files

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Sometimes (almost every month) we lost data at our clients because during run the "optimize table" from a table another app try to open (more times after a pause) the same table. We got error codes 300, 600 in Eventlog.

It seems there is a moment when the old table file nowhere, and the "open table" creates a good, but empty table, and the optimize table cannot rename the good, optimized temp table to the good filename.