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(mysql.info.gz) InnoDB checkpoints

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 15.9.2 Checkpoints
 ------------------
 
 `InnoDB' implements a checkpoint mechanism called a "fuzzy checkpoint."
 `InnoDB' will flush modified database pages from the buffer pool in
 small batches. There is no need to flush the buffer pool in one single
 batch, which would in practice stop processing of user SQL statements
 for a while.
 
 In crash recovery, `InnoDB' looks for a checkpoint label written to the
 log files. It knows that all modifications to the database before the
 label are present in the disk image of the database.  Then `InnoDB'
 scans the log files forward from the place of the checkpoint, applying
 the logged modifications to the database.
 
 `InnoDB' writes to the log files in a circular fashion.  All committed
 modifications that make the database pages in the buffer pool different
 from the images on disk must be available in the log files in case
 `InnoDB' has to do a recovery. This means that when `InnoDB' starts to
 reuse a log file in the circular fashion, it has to make sure that the
 database page images on disk contain the modifications logged in the
 log file `InnoDB' is going to reuse. In other words, `InnoDB' has to
 make a checkpoint and often this involves flushing of modified database
 pages to disk.
 
 The preceding description explains why making your log files very big
 may save disk I/O in checkpointing. It can make sense to set the total
 size of the log files as big as the buffer pool or even bigger.  The
 drawback of big log files is that crash recovery can take longer
 because there will be more logged information to apply to the database.
 
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