util.datamanager: Pad list writes to avoid crossing block boundaries

By padding items so that they do not cross block boundaries, it becomes
eaiser to delete whole blocks with fallocate() without cutting items
in half, improving efficiency of such operations.

Since list stores are used for message archives, where the most common
deletion operation would be of the oldest entires, at the top of the
file. With this, all blocks that contain items to be removed could be
deleted without needing to read, delete and write out the whole file.

1 files changed, 7 insertions, 0 deletions

diff --git a/util/datamanager.lua b/util/datamanager.lua
index 630353a9..6759592a 100644
--- a/util/datamanager.lua
+++ b/util/datamanager.lua
@@ -32,6 +32,7 @@ local path_separator = assert ( package.config:match ( "^([^\n]+)" ) , "package.
 
 local prosody = prosody;
 
+local blocksize = 0x1000;
 local raw_mkdir = lfs.mkdir;
 local atomic_append;
 local remove_blocks;
@@ -244,6 +245,12 @@ local function append(username, host, datastore, ext, data)
 	end
 
 	local pos = f:seek("end");
+	if (blocksize-(pos%blocksize)) < (#data%blocksize) then
+		-- pad to blocksize with newlines so that the next item is both on a new
+		-- block and a new line
+		atomic_append(f, ("\n"):rep(blocksize-(pos%blocksize)));
+		pos = f:seek("end");
+	end
 
 	local ok, msg = atomic_append(f, data);