From a5b9c2ca699228e82a99b672cb2796d449dcdf92 Mon Sep 17 00:00:00 2001
From: Joey Hess <joeyh@joeyh.name>
Date: Tue, 2 Jan 2024 13:56:50 -0400
Subject: [PATCH] import: Sped up import from special remote when the imported
 tree is unchanged

I saw a nearly 2 minute speed up from this, in a repo with 56000 files some
of which are preferred content of the special remote and others not. In
such a case, addBackExportExcluded has to do a lot of work, which is
unncessary when the tree is unchanged.

When using sync --content, preferred content checking of that many files
takes about 1 minute. So this speeds up sync --content by 3x.
When using git-annex import, the speed up is much larger.

Sponsored-by: Nicholas Golder-Manning on Patreon
---
 Annex/Import.hs | 31 +++++++++++++++++++------------
 CHANGELOG       |  2 ++
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/Annex/Import.hs b/Annex/Import.hs
index 023d7df1a9..5c9ac2eaaf 100644
--- a/Annex/Import.hs
+++ b/Annex/Import.hs
@@ -223,20 +223,27 @@ buildImportCommit' remote importcommitconfig mtrackingcommit imported@(History t
 		-- nothing new needs to be committed.
 		-- (This is unlikely to happen.)
 		| sametodepth h' = return Nothing
-		| otherwise = do
-			importedcommit <- case getRemoteTrackingBranchImportHistory h of
-				Nothing -> mkcommitsunconnected imported
-				Just oldimported@(History oldhc _)
-					| importeddepth == 1 ->
-						mkcommitconnected imported oldimported
-					| otherwise -> do
-						let oldimportedtrees = mapHistory historyCommitTree oldimported
-						mknewcommits oldhc oldimportedtrees imported
-			ti' <- addBackExportExcluded remote ti
-			Just <$> makeRemoteTrackingBranchMergeCommit'
-				trackingcommit importedcommit ti'
+		-- If the imported tree is unchanged,
+		-- nothing new needs to be committed.
+		| otherwise = getLastImportedTree remote >>= \case
+			Just (LastImportedTree lasttree)
+				| lasttree == ti -> return Nothing
+			_ -> gencommit trackingcommit h
 	  where
 		h'@(History t s) = mapHistory historyCommitTree h
+	
+	gencommit trackingcommit h = do
+		importedcommit <- case getRemoteTrackingBranchImportHistory h of
+			Nothing -> mkcommitsunconnected imported
+			Just oldimported@(History oldhc _)
+				| importeddepth == 1 ->
+					mkcommitconnected imported oldimported
+				| otherwise -> do
+					let oldimportedtrees = mapHistory historyCommitTree oldimported
+					mknewcommits oldhc oldimportedtrees imported
+		ti' <- addBackExportExcluded remote ti
+		Just <$> makeRemoteTrackingBranchMergeCommit'
+			trackingcommit importedcommit ti'
 
 	importeddepth = historyDepth imported
 
diff --git a/CHANGELOG b/CHANGELOG
index bb874441e5..c632bef4fb 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,8 @@
 git-annex (10.20231228) UNRELEASED; urgency=medium
 
   * info: Added "annex sizes of repositories" table to the overall display.
+  * import: Sped up import from special remote when the imported tree is
+    unchanged.
 
  -- Joey Hess <id@joeyh.name>  Fri, 29 Dec 2023 11:52:06 -0400