From the MySQL docs: --- If the transaction isolation level is REPEATABLE READ (the default level), all consistent reads within the same transaction read the snapshot established by the first such read in that transaction. You can get a fresher snapshot for your queries by committing the current transaction and after that issuing new queries. With READ COMMITTED isolation level, each consistent read within a transaction sets and reads its own fresh snapshot. --- The export script reads rows in 1000 chunks so we cannot use READ COMMITTED as it would be a new snapshot for each SELECT and so the total row count could change.
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From the MySQL docs: --- If the transaction isolation level is REPEATABLE READ (the default level), all consistent reads within the same transaction read the snapshot established by the first such read in that transaction. You can get a fresher snapshot for your queries by committing the current transaction and after that issuing new queries. With READ COMMITTED isolation level, each consistent read within a transaction sets and reads its own fresh snapshot. --- The export script reads rows in 1000 chunks so we cannot use READ COMMITTED as it would be a new snapshot for each SELECT and so the total row count could change.