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We have two MySQL servers set up with simple master-slave replication. We currently use all MyISAM tables, but may move to InnoDB in the future. Our largest tables are more then 2GB.

I would like to use the mk-table-checksum tools to run checksums on the tables, so that I can be sure that replication is working correctly.

The book High Performance MySQL and this mk-table-checksum tutorial both recommend using --sleep and --chunk-size to help avoid database blocking.

My question is in regards to the 'blocking':

  1. What sort of blocking might happen here? Is this simply referring to read locks on a table?
  2. If I don't specify --chunk-size, some of these checksums take 4-5 minutes. Will the table be locked from writes at this time?
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up vote 2 down vote accepted

It just refers to read/write locks on tables. Read locks if you're using the default checksum implementation built into MySQL; shared read locks if you're using --replicate, which does INSERT..SELECT statements.

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And according to the documentation, mk-table-checksum will only INSERT data into the table specified by --replicate. – Stefan Lasiewski Aug 31 '10 at 17:29
Thanks @Baron. Nice to have an answer from the person who wrote the tools! – Stefan Lasiewski Aug 31 '10 at 17:30

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