Document true maximum cutover timeout length #904
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When attempting a gh-ost migration, I was observed that gh-ost sets the lock timeout to 6 seconds, not 3 seconds, when attempting to lock tables. This is potentially dangerous, because a user may set this flag to 10 seconds and expect that the max table unavailability is a total of 10 seconds, when it's really 20 seconds. I observed this happening quite clearly, as gh-ost was unable to obtain the first stage lock several times. I didn't realize the docs didn't account for this total lock time. (Now, they do!)
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This is the commit message, soz for formatting in the PR:
When attempting a gh-ost migration, I was observed that gh-ost sets the
lock timeout to 6 seconds, not 3 seconds, when attempting to lock
tables. This is potentially dangerous, because a user may set this flag
to 10 seconds and expect that the max table unavailability is a total of
10 seconds, when it's really 20 seconds. I observed this happening quite
clearly, as gh-ost was unable to obtain the first stage lock several
times. I didn't realize the docs didn't account for this total lock time.
(Now, they do!)
I totally get why you would want issues to accompany PRs, but I feel like this is an easily solved problem. I can make an issue too, but I don't think it will realistically matter too much other than potentially pushing the default value down