Sped up query commands that read the git-annex branch by around 5%

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.
This commit is contained in:
Joey Hess 2020-04-09 13:54:43 -04:00
parent aba905152a
commit aeca7c2207
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14 changed files with 101 additions and 25 deletions

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@ -2,7 +2,7 @@
-
- Runtime state about the git-annex branch.
-
- Copyright 2011-2012 Joey Hess <id@joeyh.name>
- Copyright 2011-2020 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU AGPL version 3 or higher.
-}
@ -29,13 +29,56 @@ checkIndexOnce a = unlessM (indexChecked <$> getState) $ do
{- Runs an action to update the branch, if it's not been updated before
- in this run of git-annex. -}
runUpdateOnce :: Annex () -> Annex ()
runUpdateOnce a = unlessM (branchUpdated <$> getState) $ do
a
disableUpdate
runUpdateOnce :: Annex () -> Annex BranchState
runUpdateOnce a = do
st <- getState
if branchUpdated st
then return st
else do
a
let stf = \st' -> st'
{ branchUpdated = True
-- The update staged anything that was
-- journalled before, so the journal
-- does not need to be checked going
-- forward, unless new information
-- gets written to it, or unless
-- this run of git-annex needs to notice
-- changes journalled by other processes
-- while it's running.
, journalIgnorable = not $
journalNeverIgnorable st'
}
changeState stf
return (stf st)
{- Avoids updating the branch. A useful optimisation when the branch
- is known to have not changed, or git-annex won't be relying on info
- from it. -}
disableUpdate :: Annex ()
disableUpdate = changeState $ \s -> s { branchUpdated = True }
{- Called when a change is made to the journal. -}
journalChanged :: Annex ()
journalChanged = do
-- Optimisation: Typically journalIgnorable will already be True
-- (when one thing gets journalled, often other things do to),
-- so avoid an unnecessary write to the MVar that changeState
-- would do.
--
-- This assumes that another thread is not changing journalIgnorable
-- at the same time, but since runUpdateOnce is the only
-- thing that changes it, and it only runs once, that
-- should not happen.
st <- getState
when (journalIgnorable st) $
changeState $ \st' -> st' { journalIgnorable = False }
{- When git-annex is somehow interactive, eg in --batch mode,
- and needs to always notice changes made to the journal by other
- processes, this disables optimisations that avoid normally reading the
- journal.
-}
enableInteractiveJournalAccess :: Annex ()
enableInteractiveJournalAccess = changeState $
\s -> s { journalNeverIgnorable = True }