Compression and the InnoDB Redo Log Files

Compression and the InnoDB Redo Log Files
Before a compressed page is written to a data file, MySQL writes a copy of the page to the redo
log (if it has been recompressed since the last time it was written to the database). This is done to
ensure that redo logs are usable for crash recovery, even in the unlikely case that the zlib library is
upgraded and that change introduces a compatibility problem with the compressed data. Therefore,
some increase in the size of log files, or a need for more frequent checkpoints, can be expected when
using compression. The amount of increase in the log file size or checkpoint frequency depends
on the number of times compressed pages are modified in a way that requires reorganization and
recompression.
Note that compressed tables use a different file format for the redo log and the per-table tablespaces
than in MySQL 5.1 and earlier. The MySQL Enterprise Backup product supports this latest Barracuda
file format for compressed InnoDB tables. The older InnoDB Hot Backup product can only back up
tables using the file format Antelope, and thus does not support compressed InnoDB tables.
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