[PATCH v2 10/10] wal: trigger checkpoint if there are too many WALs

[Konstantin Osipov]

* Vladimir Davydov <vdavydov.dev at gmail.com> [18/12/09 00:15]:
> Closes #1082
> 
> @TarantoolBot document
> Title: Document box.cfg.checkpoint_wal_threshold
> 
> Tarantool makes checkpoints every box.cfg.checkpoint_interval seconds
> and keeps last box.cfg.checkpoint_count checkpoints. It also keeps all
> intermediate WAL files. Currently, it isn't possible to set a checkpoint
> trigger based on the sum size of WAL files, which makes it difficult to
> estimate the minimal amount of disk space that needs to be allotted to a
> Tarantool instance for storing WALs to eliminate the possibility of
> ENOSPC errors. For example, under normal conditions a Tarantool instance
> may write 1 GB of WAL files every box.cfg.checkpoint_interval seconds
> and so one may assume that 1 GB times box.cfg.checkpoint_count should be
> enough for the WAL partition, but there's no guarantee it won't write 10
> GB between checkpoints when the load is extreme.
> 
> So we've agreed that we must provide users with one more configuration
> option that could be used to impose the limit on the sum size of WAL
> files. The new option is called box.cfg.checkpoint_wal_threshold. Once
> the configured threshold is exceeded, the WAL thread notifies the
> checkpoint daemon that it's time to make a new checkpoint and delete
> old WAL files. Note, the new option only limits the size of WAL files
> created since the last checkpoint, because backup WAL files are not
> needed for recovery and can be deleted in case of emergency ENOSPC, for
> more details see tarantool/tarantool#1082, tarantool/tarantool#3397,
> tarantool/tarantool#3822.
> 
> The default value of the new option is 1 exabyte (10^18 byte), which
> actually means that the feature is disabled.

OK to push.


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Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
http://tarantool.io - www.twitter.com/kostja_osipov