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authorGravatar Joey Hess <joey@kitenet.net>2012-03-11 15:19:07 -0400
committerGravatar Joey Hess <joey@kitenet.net>2012-03-11 16:24:07 -0400
commitb086e32c63a4932fc5916bedae7abe0690da4eb0 (patch)
treee3c59401831ef04602151b18e3cfcc10c8887881 /doc/todo
parenta13949bf3794a33248611aca9ef821a6088b1b3a (diff)
unused: Reduce memory usage significantly.
Much of the memory bloat turned out to be due to getKeysReferenced containing a mapM, which is strict and buffered the whole list rather than streaming it. The other half of the bloat was due to building a temporary Set in order to call S.difference. While that is more cpu efficient, I switched to successive S.delete, since with it, I can run a whole git annex unused in less than 8 mb of memory. The whole Set of keys with content available is still stored in memory, so running unused in a repo with a whole lot of file content will still use more memory. In a repo containing 6000 files, it needed 40 mb. Note that the status command still uses the bloatful getKeysReferenced.
Diffstat (limited to 'doc/todo')
-rw-r--r--doc/todo/git-annex_unused_eats_memory.mdwn16
1 files changed, 12 insertions, 4 deletions
diff --git a/doc/todo/git-annex_unused_eats_memory.mdwn b/doc/todo/git-annex_unused_eats_memory.mdwn
index 3e9942e98..91f9a33f7 100644
--- a/doc/todo/git-annex_unused_eats_memory.mdwn
+++ b/doc/todo/git-annex_unused_eats_memory.mdwn
@@ -1,12 +1,20 @@
`git-annex unused` has to compare large sets of data
(all keys with content present in the repository,
with all keys used by files in the repository), and so
-uses more memory than git-annex typically needs; around
-50 mb when run in a repository with 80 thousand files.
+uses more memory than git-annex typically needs.
-(Used to be 80 mb, but implementation improved.)
+It used to be a lot worse (hundreds of megabytes).
-I would like to reduce this. One idea is to use a bloom filter.
+Now it only needs enough memory to store a Set of all Keys that currently
+have content in the annex. On a lightly populated repository, it runs in
+quite low memory use (like 8 mb) even if the git repo has 100 thousand
+files. On a repository with lots of file contents, it will use more.
+
+Still, I would like to reduce this to a purely constant memory use,
+as running in constant memory no matter the repo size is a git-annex design
+goal.
+
+One idea is to use a bloom filter.
For example, construct a bloom filter of all keys used by files in
the repository. Then for each key with content present, check if it's
in the bloom filter. Since there can be false positives, this might