generate more compact git-annex branch for imports

Especially from borg, where the content identifier logs
all end up being the same identical file!

But also, for other imports, the location tracking logs can,
in some cases, be identical files.

Bonus optimisation: Avoid looking up (and parsing when set)
GIT_ANNEX_VECTOR_CLOCK env var every time a log is written to.
Although the lookup does happen at startup even when no
log will be written now.

Annex.hs

@@ -72,6 +72,8 @@ import Types.IndexFiles
 import Types.CatFileHandles
 import Types.RemoteConfig
 import Types.TransferrerPool
+import Types.VectorClock
+import Annex.VectorClock.Utility
 import qualified Database.Keys.Handle as Keys
 import Utility.InodeCache
 import Utility.Url
@@ -121,6 +123,7 @@ data AnnexState = AnnexState
 	, fast :: Bool
 	, daemon :: Bool
 	, branchstate :: BranchState
+	, getvectorclock :: IO VectorClock
 	, repoqueue :: Maybe (Git.Queue.Queue Annex)
 	, catfilehandles :: CatFileHandles
 	, hashobjecthandle :: Maybe HashObjectHandle
@@ -172,6 +175,7 @@ newState c r = do
 	sc <- newTMVarIO False
 	kh <- Keys.newDbHandle
 	tp <- newTransferrerPool
+	vc <- startVectorClock
 	return $ AnnexState
 		{ repo = r
 		, repoadjustment = return
@@ -187,6 +191,7 @@ newState c r = do
 		, fast = False
 		, daemon = False
 		, branchstate = startBranchState
+		, getvectorclock = vc
 		, repoqueue = Nothing
 		, catfilehandles = catFileHandlesNonConcurrent
 		, hashobjecthandle = Nothing

Annex/Import.hs

@@ -38,6 +38,7 @@ import Annex.RemoteTrackingBranch
 import Annex.HashObject
 import Annex.Transfer
 import Annex.CheckIgnore
+import Annex.VectorClock
 import Command
 import Backend
 import Types.Key
@@ -342,8 +343,17 @@ importKeys remote importtreeconfig importcontent thirdpartypopulated importablec
 		bracket CIDDb.openDb CIDDb.closeDb $ \db -> do
 			CIDDb.needsUpdateFromLog db
 				>>= maybe noop (CIDDb.updateFromLog db)
-			go False cidmap importing importablecontents db
+			(run (go False cidmap importing importablecontents db))
   where
+	-- When not importing content, reuse the same vector
+	-- clock for all state that's recorded. This can save
+	-- a little bit of disk space. Individual file downloads
+	-- while downloading take too long for this optimisation
+	-- to be safe to do.
+	run a
+		| importcontent = a
+		| otherwise = reuseVectorClockWhile a
+
 	go oldversion cidmap importing (ImportableContents l h) db = do
 		largematcher <- largeFilesMatcher
 		jobs <- forM l $ \i ->

Annex/VectorClock.hs

@@ -3,42 +3,54 @@
  - We don't have a way yet to keep true distributed vector clocks.
  - The next best thing is a timestamp.
  -
- - Copyright 2017-2019 Joey Hess <id@joeyh.name>
+ - Copyright 2017-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
 
-module Annex.VectorClock where
+module Annex.VectorClock (
+	module Annex.VectorClock,
+	module Types.VectorClock,
+) where
 
-import Data.Time.Clock.POSIX
-import Data.ByteString.Builder
-import Control.Applicative
-import Prelude
-
-import Utility.Env
+import Types.VectorClock
+import Annex.Common
+import qualified Annex
 import Utility.TimeStamp
-import Utility.QuickCheck
+
+import Data.ByteString.Builder
 import qualified Data.Attoparsec.ByteString.Lazy as A
 
--- | Some very old logs did not have any time stamp at all;
--- Unknown is used for those.
-data VectorClock = Unknown | VectorClock POSIXTime
-	deriving (Eq, Ord, Show)
+currentVectorClock :: Annex VectorClock
+currentVectorClock = liftIO =<< Annex.getState Annex.getvectorclock
 
--- Unknown is oldest.
-prop_VectorClock_sane :: Bool
-prop_VectorClock_sane = Unknown < VectorClock 1
-
-instance Arbitrary  VectorClock where
-	arbitrary = VectorClock <$> arbitrary
-
-currentVectorClock :: IO VectorClock
-currentVectorClock = go =<< getEnv "GIT_ANNEX_VECTOR_CLOCK"
+-- Runs the action and uses the same vector clock throughout.
+--
+-- When the action modifies several files in the git-annex branch,
+-- this can cause less space to be used, since the same vector clock
+-- value is used, which can compress better.
+--
+-- However, this should not be used when running a long-duration action,
+-- because the vector clock is based on the start of the action, and not on 
+-- the later points where it writes changes. For example, if this were
+-- used across downloads of several files, the location log information
+-- would have an earlier vector clock than necessary, which might cause it
+-- to be disregarded in favor of other information that was collected
+-- at an earlier point in time than when the transfers completted and the
+-- log was written.
+reuseVectorClockWhile :: Annex a -> Annex a
+reuseVectorClockWhile = bracket setup cleanup . const
   where
-	go Nothing = VectorClock <$> getPOSIXTime
-	go (Just s) = case parsePOSIXTime s of
-		Just t -> return (VectorClock t)
-		Nothing -> VectorClock <$> getPOSIXTime
+	setup = do
+		origget <- Annex.getState Annex.getvectorclock
+		vc <- liftIO origget
+		use (pure vc)
+		return origget
+
+	cleanup origget = use origget
+
+	use vc = Annex.changeState $ \s ->
+		s { Annex.getvectorclock = vc }
 
 formatVectorClock :: VectorClock -> String
 formatVectorClock Unknown = "0"

Annex/VectorClock/Utility.hs

@@ -0,0 +1,23 @@
+{- git-annex vector clock utilities
+ -
+ - Copyright 2017-2020 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module Annex.VectorClock.Utility where
+
+import Data.Time.Clock.POSIX
+
+import Types.VectorClock
+import Utility.Env
+import Utility.TimeStamp
+
+startVectorClock :: IO (IO VectorClock)
+startVectorClock = go =<< getEnv "GIT_ANNEX_VECTOR_CLOCK"
+  where
+	go Nothing = timebased
+	go (Just s) = case parsePOSIXTime s of
+		Just t -> return (pure (VectorClock t))
+		Nothing -> timebased
+	timebased = return (VectorClock <$> getPOSIXTime)

Command/Forget.hs

@@ -35,7 +35,7 @@ seek = commandAction . start
 
 start :: ForgetOptions -> CommandStart
 start o = starting "forget" ai si $ do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	let basets = addTransition c ForgetGitHistory noTransitions
 	let ts = if dropDead o
 		then addTransition c ForgetDeadRemotes basets

Command/MetaData.hs

@@ -74,7 +74,7 @@ optParser desc = MetaDataOptions
 seek :: MetaDataOptions -> CommandSeek
 seek o = case batchOption o of
 	NoBatch -> do
-		c <- liftIO currentVectorClock
+		c <- currentVectorClock
 		let ww = WarnUnmatchLsFiles
 		let seeker = AnnexedFileSeeker
 			{ startAction = start c o
@@ -188,7 +188,7 @@ startBatch (si, (i, (MetaData m))) = case i of
 			, keyOptions = Nothing
 			, batchOption = NoBatch
 			}
-		t <- liftIO currentVectorClock
+		t <- currentVectorClock
 		-- It would be bad if two batch mode changes used exactly
 		-- the same timestamp, since the order of adds and removals
 		-- of the same metadata value would then be indeterminate.

Logs/Activity.hs

@@ -27,7 +27,7 @@ data Activity
 
 recordActivity :: Activity -> UUID -> Annex ()
 recordActivity act uuid = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change activityLog $
 		buildLogOld buildActivity
 			. changeLog c uuid (Right act)

Logs/Chunk.hs

@@ -35,7 +35,7 @@ import qualified Data.Map as M
 
 chunksStored :: UUID -> Key -> ChunkMethod -> ChunkCount -> Annex ()
 chunksStored u k chunkmethod chunkcount = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	config <- Annex.getGitConfig
 	Annex.Branch.change (chunkLogFile config k) $
 		buildLog . changeMapLog c (u, chunkmethod) chunkcount . parseLog

Logs/Config.hs

@@ -34,7 +34,7 @@ setGlobalConfig name new = do
 
 setGlobalConfig' :: ConfigKey -> ConfigValue -> Annex ()
 setGlobalConfig' name new = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change configLog $ 
 		buildGlobalConfig . changeMapLog c name new . parseGlobalConfig
 

Logs/ContentIdentifier.hs

@@ -30,7 +30,7 @@ import qualified Data.List.NonEmpty as NonEmpty
 -- so ones that were recorded before are preserved.
 recordContentIdentifier :: RemoteStateHandle -> ContentIdentifier -> Key -> Annex ()
 recordContentIdentifier (RemoteStateHandle u) cid k = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	config <- Annex.getGitConfig
 	Annex.Branch.maybeChange (remoteContentIdentifierLogFile config k) $
 		addcid c . parseLog

Logs/Difference.hs

@@ -25,7 +25,7 @@ import Logs.Difference.Pure
 
 recordDifferences :: Differences -> UUID -> Annex ()
 recordDifferences ds@(Differences {}) uuid = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change differenceLog $
 		buildLogOld byteString 
 			. changeLog c uuid (encodeBS $ showDifferences ds) 

Logs/Export.hs

@@ -92,7 +92,7 @@ getExport remoteuuid = nub . mapMaybe get . M.toList . simpleMap
 -- This is called before any changes are made to the remote.
 recordExportBeginning :: UUID -> Git.Ref -> Annex ()
 recordExportBeginning remoteuuid newtree = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	u <- getUUID
 	let ep = ExportParticipants { exportFrom = u, exportTo = remoteuuid }
 	old <- fromMaybe (Exported emptyTree [])
@@ -127,7 +127,7 @@ recordExportTreeish t =
 -- forward in lock-step.
 recordExportUnderway :: UUID -> ExportChange -> Annex ()
 recordExportUnderway remoteuuid ec = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	u <- getUUID
 	let ep = ExportParticipants { exportFrom = u, exportTo = remoteuuid }
 	let exported = Exported (newTreeish ec) []

Logs/Group.hs

@@ -38,7 +38,7 @@ lookupGroups u = (fromMaybe S.empty . M.lookup u) . groupsByUUID <$> groupMap
 groupChange :: UUID -> (S.Set Group -> S.Set Group) -> Annex ()
 groupChange uuid@(UUID _) modifier = do
 	curr <- lookupGroups uuid
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change groupLog $
 		buildLogOld buildGroup . changeLog c uuid (modifier curr) . parseLogOld parseGroup
 	

Logs/MetaData.hs

@@ -103,7 +103,7 @@ addMetaData = addMetaData' metaDataLogFile
 
 addMetaData' :: (GitConfig -> Key -> RawFilePath) -> Key -> MetaData -> Annex ()
 addMetaData' getlogfile k metadata = 
-	addMetaDataClocked' getlogfile k metadata =<< liftIO currentVectorClock
+	addMetaDataClocked' getlogfile k metadata =<< currentVectorClock
 
 {- Reusing the same VectorClock when making changes to the metadata
  - of multiple keys is a nice optimisation. The same metadata lines

Logs/Multicast.hs

@@ -25,7 +25,7 @@ newtype Fingerprint = Fingerprint String
 
 recordFingerprint :: Fingerprint -> UUID -> Annex ()
 recordFingerprint fp uuid = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change multicastLog $
 		buildLogOld buildFindgerPrint
 			. changeLog c uuid fp

Logs/PreferredContent/Raw.hs

@@ -30,7 +30,7 @@ requiredContentSet = setLog requiredContentLog
 
 setLog :: RawFilePath -> UUID -> PreferredContentExpression -> Annex ()
 setLog logfile uuid@(UUID _) val = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change logfile $
 		buildLogOld buildPreferredContentExpression
 		. changeLog c uuid val
@@ -44,7 +44,7 @@ setLog _ NoUUID _ = error "unknown UUID; cannot modify"
 {- Changes the preferred content configuration of a group. -}
 groupPreferredContentSet :: Group -> PreferredContentExpression -> Annex ()
 groupPreferredContentSet g val = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change groupPreferredContentLog $
 		buildGroupPreferredContent
 		. changeMapLog c g val 

Logs/Presence.hs

@@ -51,7 +51,7 @@ readLog = parseLog <$$> Annex.Branch.get
 {- Generates a new LogLine with the current time. -}
 logNow :: LogStatus -> LogInfo -> Annex LogLine
 logNow s i = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	return $ LogLine c s i
 
 {- Reads a log and returns only the info that is still in effect. -}

Logs/Remote.hs

@@ -32,7 +32,7 @@ import qualified Data.Map as M
 {- Adds or updates a remote's config in the log. -}
 configSet :: UUID -> RemoteConfig -> Annex ()
 configSet u cfg = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change remoteLog $
 		buildRemoteConfigLog
 			. changeLog c u (removeSameasInherited cfg)

Logs/RemoteState.hs

@@ -26,7 +26,7 @@ type RemoteState = String
 
 setRemoteState :: RemoteStateHandle -> Key -> RemoteState -> Annex ()
 setRemoteState (RemoteStateHandle u) k s = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	config <- Annex.getGitConfig
 	Annex.Branch.change (remoteStateLogFile config k) $
 		buildRemoteState . changeLog c u s . parseRemoteState

Logs/Schedule.hs

@@ -32,7 +32,7 @@ import Logs.File
 
 scheduleSet :: UUID -> [ScheduledActivity] -> Annex ()
 scheduleSet uuid@(UUID _) activities = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change scheduleLog $
 		buildLogOld byteString 
 			. changeLog c uuid (encodeBS val)

Logs/SingleValue.hs

@@ -33,6 +33,6 @@ getLog = newestValue <$$> readLog
 
 setLog :: (SingleValueSerializable v) => RawFilePath -> v -> Annex ()
 setLog f v = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	let ent = LogEntry c v
 	Annex.Branch.change f $ \_old -> buildLog (S.singleton ent)

Logs/Trust/Basic.hs

@@ -22,7 +22,7 @@ import Logs.Trust.Pure as X
 {- Changes the trust level for a uuid in the trustLog. -}
 trustSet :: UUID -> TrustLevel -> Annex ()
 trustSet uuid@(UUID _) level = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change trustLog $
 		buildLogOld buildTrustLevel .
 			changeLog c uuid level .

Logs/UUID.hs

@@ -31,7 +31,7 @@ import qualified Data.Attoparsec.ByteString.Lazy as A
 {- Records a description for a uuid in the log. -}
 describeUUID :: UUID -> UUIDDesc -> Annex ()
 describeUUID uuid desc = do
-	c <- liftIO currentVectorClock
+	c <- currentVectorClock
 	Annex.Branch.change uuidLog $
 		buildLogOld buildUUIDDesc . changeLog c uuid desc . parseUUIDLog
 

Types/VectorClock.hs

@@ -0,0 +1,29 @@
+{- git-annex vector clocks
+ -
+ - We don't have a way yet to keep true distributed vector clocks.
+ - The next best thing is a timestamp.
+ -
+ - Copyright 2017-2020 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module Types.VectorClock where
+
+import Data.Time.Clock.POSIX
+import Control.Applicative
+import Prelude
+
+import Utility.QuickCheck
+
+-- | Some very old logs did not have any time stamp at all;
+-- Unknown is used for those.
+data VectorClock = Unknown | VectorClock POSIXTime
+	deriving (Eq, Ord, Show)
+
+-- Unknown is oldest.
+prop_VectorClock_sane :: Bool
+prop_VectorClock_sane = Unknown < VectorClock 1
+
+instance Arbitrary  VectorClock where
+	arbitrary = VectorClock <$> arbitrary

doc/todo/use_same_vector_clock_for_content_identifier_updates_in_import.mdwn

@@ -11,3 +11,6 @@ As a bonus, since borg uses the same content identifiers for all keys
 (""), implementing this would make the content of the logs all identical,
 and so avoid any overhead entirely. Well.. perhaps that's my actual
 motivation. ;-) --[[Joey]]
+
+> [[done]], though reuseVectorClockWhile could be used in other places
+> perhaps. --[[Joey]]

git-annex.cabal

@@ -670,6 +670,7 @@ Executable git-annex
     Annex.UUID
     Annex.Url
     Annex.VectorClock
+    Annex.VectorClock.Utility
     Annex.VariantFile
     Annex.Version
     Annex.View
@@ -1035,6 +1036,7 @@ Executable git-annex
     Types.TrustLevel
     Types.UUID
     Types.UrlContents
+    Types.VectorClock
     Types.View
     Types.WorkerPool
     Upgrade