# HG changeset patch
# User Kim Alvefur <zash@zash.se>
# Date 1686091170 -7200
# Node ID affaf6d08d26998e09c94ab057e3be8c9b74edac
# Parent  b57f45165e1e5831218805cc3b0f037448a0d1aa
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.

diff -r b57f45165e1e -r affaf6d08d26 util/datamanager.lua
--- a/util/datamanager.lua	Wed Jul 12 11:45:12 2023 +0200
+++ b/util/datamanager.lua	Wed Jun 07 00:39:30 2023 +0200
@@ -32,6 +32,7 @@
 
 local prosody = prosody;
 
+local blocksize = 0x1000;
 local raw_mkdir = lfs.mkdir;
 local atomic_append;
 local remove_blocks;
@@ -244,6 +245,12 @@
 	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);