aeca7c2207
The only price paid is one additional MVar read per write to the journal. Presumably writing a journal file dominiates over a MVar read time by several orders of magnitude. --batch does not get the speedup because then it needs to notice when another process has made a change. Also made the assistant and other damon modes bypass the optimisation, which would not help them anyway.
33 lines
1.5 KiB
Markdown
33 lines
1.5 KiB
Markdown
Often a command will need to read a number of files from the git-annex
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branch, and it uses getJournalFile for each to check for any journalled
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change that has not reached the branch. But typically, the journal is empty
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and in such a case, that's a lot of time spent trying to open journal files
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that DNE.
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Profiling eg, `git annex find --in web` shows things called by getJournalFile
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use around 5% of runtime.
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What if, once at startup, it checked if the journal was entirely empty.
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If so, it can remember that, and avoid reading journal files.
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Perhaps paired with staging the journal if it's not empty.
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When a process writes to the journal, it will need to update its state
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to remember it's no longer empty.
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This could lead to behavior changes in some cases where one command is
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writing changes and another command used to read them from the journal and
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may no longer do so. But any such behavior change is of a behavior that
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used to involve a race; the reader could just as well be ahead of the
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writer and it would have already behaved as it would after the change.
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> Hmm, not so fast. If the user has two --batch processes, one that makes
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> changes and the other that queries, they will expect the querying process
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> to see the changes after they were made. There's no race, the user can
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> control which process runs by feeding batch inputs to them.
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>
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> So, --batch and the assistant, as well as batch-like things that don't
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> use --batch will need to disable this optimisation it seems. --[[Joey]]
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[[!tag confirmed]]
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>> [[done]] speedup was around 5% --[[Joey]]
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