sync: use log to track adjusted branch needs updating

Speeds up sync in an adjusted branch by avoiding re-adjusting the branch
unncessarily, particularly when it is adjusted with --hide-missing or
--unlock-present.

When there are a lot of files, that was the majority of the time of a
--no-content sync.

Uses a log file, which is updated when content presence changes. This
adds a little bit of overhead to every file get/drop when on such an
adjusted branch. The overhead is minimal for get of any size of file,
but might be noticable for drop in some cases. It seems like a reasonable
trade-off. It would be possible to update the log file only at the end, but
then it would not happen if the command is interrupted.

When not in an adjusted branch, there should be no additional overhead.
(getCurrentBranch is an MVar read, and it avoids the MVar read of
getGitConfig.)

Note that this does not deal with situations such as:
git checkout master, git-annex get, git checkout adjusted branch,
git-annex sync. The sync won't know that the adjusted branch needs to be
updated. Dealing with that would add overhead to operation in non-adjusted
branches, which I don't like. Also, there are other situations like having
two adjusted branches that both need to be updated like this, and switching
between them and sync not updating.

This does mean a behavior change to sync, since it did previously deal
with those situations. But, the documentation did not say that it did.
The man pages only talk about sync updating the adjusted branch after
it transfers content.

I did consider making sync keep track of content it transferred (and
dropped) and only update the adjusted branch then, not to catch up to other
changes made previously. That would perform better. But it seemed rather
hard to implement, and also it would have problems with races with a
concurrent get/drop, which this implementation avoids.

And it seemed pretty likely someone had gotten used to get/drop followed by
sync updating the branch. It seems much less likely someone is switching
branches, doing get/drop, and then switching back and expecting sync to update
the branch.

Re-running git-annex adjust still does a full re-adjusting of the branch,
for anyone who needs that.

Sponsored-by: Leon Schuermann on Patreon

Annex/AdjustedBranch.hs

@@ -67,7 +67,9 @@ import Types.CleanupActions
 import qualified Database.Keys
 import Config
 import Logs.View (is_branchView)
+import Logs.AdjustedBranchUpdate
 
+import Data.Time.Clock.POSIX
 import qualified Data.Map as M
 
 class AdjustTreeItem t where
@@ -223,9 +225,13 @@ enterAdjustedBranch adj = inRepo Git.Branch.current >>= \case
 					]
 				return False
 			, do
+				starttime <- liftIO getPOSIXTime
 				b <- preventCommits $ const $ 
 					adjustBranch adj origbranch
-				checkoutAdjustedBranch b False
+				ok <- checkoutAdjustedBranch b False
+				when ok $
+					recordAdjustedBranchUpdateFinished starttime
+				return ok
 			)
 
 checkoutAdjustedBranch :: AdjBranch -> Bool -> Annex Bool
@@ -304,18 +310,22 @@ updateAdjustedBranch adj (AdjBranch currbranch) origbranch
 adjustedBranchRefresh :: AssociatedFile -> Annex a -> Annex a
 adjustedBranchRefresh _af a = do
 	r <- a
-	annexAdjustedBranchRefresh <$> Annex.getGitConfig >>= \case
-		0 -> return ()
-		n -> go n
+	go
 	return r
   where
-	go n = getCurrentBranch >>= \case
+	go = getCurrentBranch >>= \case
 		(Just origbranch, Just adj) ->
-			unless (adjustmentIsStable adj) $
-				ifM (checkcounter n)
-					( update adj origbranch
+			unless (adjustmentIsStable adj) $ do
+				recordAdjustedBranchUpdateNeeded
+				n <- annexAdjustedBranchRefresh <$> Annex.getGitConfig
+				unless (n == 0) $ ifM (checkcounter n)
+					-- This is slow, it would be better to incrementally
+					-- adjust the AssociatedFile, and only call this once
+					-- at shutdown to handle cases where not all
+					-- AssociatedFiles are known.
+					( adjustedBranchRefreshFull' adj origbranch
 					, Annex.addCleanupAction AdjustedBranchUpdate $
-						adjustedBranchRefreshFull adj origbranch
+						adjustedBranchRefreshFull' adj origbranch
 					)
 		_ -> return ()
 	
@@ -329,23 +339,24 @@ adjustedBranchRefresh _af a = do
 			    !s' = s { Annex.adjustedbranchrefreshcounter = c' }
 			    in pure (s', enough)
 
-	-- This is slow, it would be better to incrementally
-	-- adjust the AssociatedFile, and only call this once
-	-- at shutdown to handle cases where not all
-	-- AssociatedFiles are known.
-	update adj origbranch =
-		adjustedBranchRefreshFull adj origbranch
-
 {- Slow, but more dependable version of adjustedBranchRefresh that
  - does not rely on all AssociatedFiles being known. -}
 adjustedBranchRefreshFull :: Adjustment -> OrigBranch -> Annex ()
-adjustedBranchRefreshFull adj origbranch = do
+adjustedBranchRefreshFull adj origbranch =
+	whenM isAdjustedBranchUpdateNeeded $ do
+		adjustedBranchRefreshFull' adj origbranch
+
+adjustedBranchRefreshFull' :: Adjustment -> OrigBranch -> Annex ()
+adjustedBranchRefreshFull' adj origbranch = do
 	-- Restage pointer files so modifications to them due to get/drop
 	-- do not prevent checking out the updated adjusted branch.
 	restagePointerFiles =<< Annex.gitRepo
+	starttime <- liftIO getPOSIXTime
 	let adjbranch = originalToAdjusted origbranch adj
-	unlessM (updateAdjustedBranch adj adjbranch origbranch) $
-		warning "Updating adjusted branch failed."
+	ifM (updateAdjustedBranch adj adjbranch origbranch)
+		( recordAdjustedBranchUpdateFinished starttime
+		, warning "Updating adjusted branch failed."
+		)
 
 adjustToCrippledFileSystem :: Annex ()
 adjustToCrippledFileSystem = do

Annex/Locations.hs

@@ -52,6 +52,8 @@ module Annex.Locations (
 	gitAnnexRestageLog,
 	gitAnnexRestageLogOld,
 	gitAnnexRestageLock,
+	gitAnnexAdjustedBranchUpdateLog,
+	gitAnnexAdjustedBranchUpdateLock,
 	gitAnnexMoveLog,
 	gitAnnexMoveLock,
 	gitAnnexExportDir,
@@ -395,6 +397,14 @@ gitAnnexRestageLogOld r = gitAnnexDir r P.</> "restage.old"
 gitAnnexRestageLock :: Git.Repo -> RawFilePath
 gitAnnexRestageLock r = gitAnnexDir r P.</> "restage.lck"
 
+{- .git/annex/adjust.log is used to log when the adjusted branch needs to
+ - be updated. -}
+gitAnnexAdjustedBranchUpdateLog :: Git.Repo -> RawFilePath
+gitAnnexAdjustedBranchUpdateLog r = gitAnnexDir r P.</> "adjust.log"
+
+gitAnnexAdjustedBranchUpdateLock :: Git.Repo -> RawFilePath
+gitAnnexAdjustedBranchUpdateLock r = gitAnnexDir r P.</> "adjust.lck"
+
 {- .git/annex/move.log is used to log moves that are in progress,
  - to better support resuming an interrupted move. -}
 gitAnnexMoveLog :: Git.Repo -> RawFilePath

CHANGELOG

@@ -81,6 +81,9 @@ git-annex (10.20230408) UNRELEASED; urgency=medium
   * Some other speedups to importing trees from special remotes.
   * Cache negative lookups of global numcopies and mincopies. 
     Speeds up eg git-annex sync --content by up to 50%.
+  * Speed up sync in an adjusted branch by avoiding re-adjusting the branch
+    unncessarily, particularly when it is adjusted with --hide-missing
+    or --unlock-present.
 
  -- Joey Hess <id@joeyh.name>  Sat, 08 Apr 2023 13:57:18 -0400
 

Logs/AdjustedBranchUpdate.hs

@@ -0,0 +1,84 @@
+{- git-annex log file that indicates when the adjusted branch needs to be
+ - updated due to changes in content availability.
+ -
+ - Copyright 2023 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+{-# LANGUAGE OverloadedStrings #-}
+
+module Logs.AdjustedBranchUpdate (
+	recordAdjustedBranchUpdateNeeded,
+	recordAdjustedBranchUpdateFinished,
+	isAdjustedBranchUpdateNeeded,
+) where
+
+import Annex.Common
+import Logs.File
+import Utility.TimeStamp
+
+import qualified Data.ByteString.Lazy as L
+import Data.Time.Clock.POSIX
+
+-- | Updates the log to indicate that an update is needed.
+recordAdjustedBranchUpdateNeeded :: Annex ()
+recordAdjustedBranchUpdateNeeded = do
+	now <- liftIO getPOSIXTime
+	logf <- fromRepo gitAnnexAdjustedBranchUpdateLog
+	lckf <- fromRepo gitAnnexAdjustedBranchUpdateLock
+	-- Replace any other log entries, because an update is needed now,
+	-- so an entry that says an update finished must be in the past.
+	-- And, if there were clock skew, an entry that says an update is
+	-- needed in the future would be wrong information.
+	modifyLogFile logf lckf (const [formatAdjustLog True now])
+
+-- | Called after an update has finished. The time is when the update
+-- started. If recordAdjustedBranchUpdateNeeded was called during the
+-- update, the log is left indicating that an update is still needed.
+recordAdjustedBranchUpdateFinished :: POSIXTime -> Annex ()
+recordAdjustedBranchUpdateFinished starttime = do
+	now <- liftIO getPOSIXTime
+	logf <- fromRepo gitAnnexAdjustedBranchUpdateLog
+	lckf <- fromRepo gitAnnexAdjustedBranchUpdateLock
+	modifyLogFile logf lckf (go now)
+  where
+	go now logged
+		| null $ filter (isnewer now) $ mapMaybe parseAdjustLog logged =
+			[formatAdjustLog False starttime]
+		| otherwise = logged
+	
+	-- If the logged time is in the future, there was clock skew,
+	-- so disregard that log entry.
+	isnewer now (_, loggedtime) = 
+		loggedtime >= starttime && loggedtime <= now
+
+isAdjustedBranchUpdateNeeded :: Annex Bool
+isAdjustedBranchUpdateNeeded = do
+	logf <- fromRepo gitAnnexAdjustedBranchUpdateLog
+	lckf <- fromRepo gitAnnexAdjustedBranchUpdateLock
+	calcLogFile logf lckf Nothing go >>= return . \case
+		Just b -> b
+		-- No log, so assume an update is needed.
+		-- This handles upgrades from before this log was written.
+		Nothing -> True
+  where
+ 	go l p = case parseAdjustLog l of
+		Nothing -> p
+		Just (b, _t) -> case p of
+			Nothing -> Just b
+			Just b' -> Just (b' || b)
+
+formatAdjustLog :: Bool -> POSIXTime -> L.ByteString
+formatAdjustLog b t = encodeBL (show t) <> " " <> if b then "1" else "0"
+
+parseAdjustLog :: L.ByteString -> Maybe (Bool, POSIXTime)
+parseAdjustLog l = 
+	let (ts, bs) = separate (== ' ') (decodeBL l)
+	in do
+		b <- case bs of
+			"1" -> Just True
+			"0" -> Just False
+			_ -> Nothing
+		t <- parsePOSIXTime ts
+		return (b, t)

git-annex.cabal

@@ -898,6 +898,7 @@ Executable git-annex
     Limit.Wanted
     Logs
     Logs.Activity
+    Logs.AdjustedBranchUpdate
     Logs.Chunk
     Logs.Chunk.Pure
     Logs.Config