Enable BUFFERS with EXPLAIN ANALYZE by default

The topic of turning EXPLAIN's BUFFERS option on with the ANALYZE option
has come up a few times over the past few years.  In many ways, doing this
seems like a good idea as it may be more obvious to users why a given
query is running more slowly than they might expect.  Also, from my own
(David's) personal experience, I've seen users posting to the mailing
lists with two identical plans, one slow and one fast asking why their
query is sometimes slow.  In many cases, this is due to additional reads.
Having BUFFERS on by default may help reduce some of these questions, and
if not, make it more obvious to the user before they post, or save a
round-trip to the mailing list when additional I/O effort is the cause of
the slowness.

The general consensus is that we want BUFFERS on by default with
ANALYZE.  However, there were more than zero concerns raised with doing
so.  The primary reason against is the additional verbosity, making it
harder to read large plans.  Another concern was that buffer information
isn't always useful so may not make sense to have it on by default.

It's currently December, so let's commit this to see if anyone comes
forward with a strong objection against making this change.  We have over
half a year remaining in the v18 cycle where we could still easily consider
reverting this if someone were to come forward with a convincing enough
reason as to why doing this is a bad idea.

There were two patches independently submitted to achieve this goal, one
by me and the other by Guillaume.  This commit is a mix of both of these
patches with some additional work done by me to adjust various
additional places in the documentation which include EXPLAIN ANALYZE
output.

Author: Guillaume Lelarge, David Rowley
Reviewed-by: Robert Haas, Greg Sabino Mullane, Michael Christofides
Discussion: https://postgr.es/m/CANNMO++W7MM8T0KyXN3ZheXXt-uLVM3aEtZd+WNfZ=obxffUiA@mail.gmail.com

1 files changed, 4 insertions, 4 deletions

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 372fe6dad15..3900522ccb5 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -3904,7 +3904,7 @@ ALTER FOREIGN TABLE async_p2 OPTIONS (use_remote_estimate 'true');
 
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT * FROM local_tbl, async_pt WHERE local_tbl.a = async_pt.a AND local_tbl.c = 'bar';
-EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
 SELECT * FROM local_tbl, async_pt WHERE local_tbl.a = async_pt.a AND local_tbl.c = 'bar';
 SELECT * FROM local_tbl, async_pt WHERE local_tbl.a = async_pt.a AND local_tbl.c = 'bar';
 
@@ -3979,13 +3979,13 @@ ANALYZE local_tbl;
 
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT * FROM local_tbl t1 LEFT JOIN (SELECT *, (SELECT count(*) FROM async_pt WHERE a < 3000) FROM async_pt WHERE a < 3000) t2 ON t1.a = t2.a;
-EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
 SELECT * FROM local_tbl t1 LEFT JOIN (SELECT *, (SELECT count(*) FROM async_pt WHERE a < 3000) FROM async_pt WHERE a < 3000) t2 ON t1.a = t2.a;
 SELECT * FROM local_tbl t1 LEFT JOIN (SELECT *, (SELECT count(*) FROM async_pt WHERE a < 3000) FROM async_pt WHERE a < 3000) t2 ON t1.a = t2.a;
 
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT * FROM async_pt t1 WHERE t1.b === 505 LIMIT 1;
-EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
 SELECT * FROM async_pt t1 WHERE t1.b === 505 LIMIT 1;
 SELECT * FROM async_pt t1 WHERE t1.b === 505 LIMIT 1;
 
@@ -4037,7 +4037,7 @@ DELETE FROM async_p1;
 DELETE FROM async_p2;
 DELETE FROM async_p3;
 
-EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
+EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
 SELECT * FROM async_pt;
 
 -- Clean up