docs: note wider impact of --checkers=N on parallelism #6280

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mirekphd 2022-06-27 20:33:07 +02:00 committed by GitHub
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@ -639,12 +639,22 @@ objects to transfer is held in memory before the transfers start.
### --checkers=N ###
The number of checkers to run in parallel. Checkers do the equality
checking of files during a sync. For some storage systems (e.g. S3,
Swift, Dropbox) this can take a significant amount of time so they are
run in parallel.
Originally controlling just the number of file checkers to run in parallel,
e.g. by `rclone copy`. Now a fairly universal parallelism control
used by `rclone` in several places.
The default is to run 8 checkers in parallel.
Note: checkers do the equality checking of files during a sync.
For some storage systems (e.g. S3, Swift, Dropbox) this can take
a significant amount of time so they are run in parallel.
The default is to run 8 checkers in parallel. However, in case
of slow-reacting backends you may need to lower (rather than increase)
this default by setting `--checkers` to 4 or less threads. This is
especially advised if you are experiencing backend server crashes
during file checking phase (e.g. on subsequent or top-up backups
where little or no file copying is done and checking takes up
most of the time). Increase this setting only with utmost care,
while monitoring your server health and file checking throughput.
### -c, --checksum ###