From 812ced024a7edea7dda1634fe926936c20a22f93 Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Thu, 5 Apr 2018 10:31:53 +0900 Subject: [PATCH 2/2] Enforce ordering of data chunks fetched in pg_rewind for libpq transfer This is good for performance, as this gives a sequential behavior to the rewind operation, and also limits the number of files opened and closed when applying data chunks. Author: Christian H. Author: Michael Paquier Discussion: https://postgr.es/m/20180104200633.17004.16377%40wrigleys.postgresql.org --- src/bin/pg_rewind/libpq_fetch.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/src/bin/pg_rewind/libpq_fetch.c b/src/bin/pg_rewind/libpq_fetch.c index 5914b15017..880c6553ea 100644 --- a/src/bin/pg_rewind/libpq_fetch.c +++ b/src/bin/pg_rewind/libpq_fetch.c @@ -501,12 +501,18 @@ libpq_executeFileMap(filemap_t *map) /* * We've now copied the list of file ranges that we need to fetch to the - * temporary table. Now, actually fetch all of those ranges. + * temporary table. Now, actually fetch all of those ranges. The elements + * fetched are ordered to ensure that the set of chunks applying to one + * are processed successively. This gives a sequential behavior to the + * rewind, which is good for performance especially on large files, and + * limites the back-and-forth movements to open and close multiple times + * the same file. */ sql = "SELECT path, begin,\n" " pg_read_binary_file(path, begin, len, true) AS chunk\n" - "FROM fetchchunks\n"; + "FROM fetchchunks\n" + "ORDER BY path, begin\n"; receiveFileChunks(sql); } -- 2.16.3