Possible performance regression in version 10.1 with pgbench read-write tests.

Hi all,

When I was trying to do read-write pgbench bench-marking of PostgreSQL
9.6.6 vs 10.1 I found PostgreSQL 10.1 regresses against 9.6.6 in some
cases.

Non Default settings and test
======================
Server:
./postgres -c shared_buffers=8GB -N 200 -c min_wal_size=15GB -c
max_wal_size=20GB -c checkpoint_timeout=900 -c
maintenance_work_mem=1GB -c checkpoint_completion_target=0.9 &

Pgbench:
CASE 1: when data fits shared buffers.
./pgbench -i -s 1000 postgres

CASE 2: when data exceeds shared buffers.
./pgbench -i -s 1000 postgres

./pgbench -c $threads -j $threads -T 1800 -M prepared postgres

Script "perf_buff_mgmt_write-2.sh" which is added below can be used to run same.

Machine : "cthulhu" 8 node numa machine with 128 hyper threads.
===================================================
>numactl --hardware
available: 8 nodes (0-7)
node 0 cpus: 0 65 66 67 68 69 70 71 96 97 98 99 100 101 102 103
node 0 size: 65498 MB
node 0 free: 37885 MB
node 1 cpus: 72 73 74 75 76 77 78 79 104 105 106 107 108 109 110 111
node 1 size: 65536 MB
node 1 free: 31215 MB
node 2 cpus: 80 81 82 83 84 85 86 87 112 113 114 115 116 117 118 119
node 2 size: 65536 MB
node 2 free: 15331 MB
node 3 cpus: 88 89 90 91 92 93 94 95 120 121 122 123 124 125 126 127
node 3 size: 65536 MB
node 3 free: 36774 MB
node 4 cpus: 1 2 3 4 5 6 7 8 33 34 35 36 37 38 39 40
node 4 size: 65536 MB
node 4 free: 62 MB
node 5 cpus: 9 10 11 12 13 14 15 16 41 42 43 44 45 46 47 48
node 5 size: 65536 MB
node 5 free: 9653 MB
node 6 cpus: 17 18 19 20 21 22 23 24 49 50 51 52 53 54 55 56
node 6 size: 65536 MB
node 6 free: 50209 MB
node 7 cpus: 25 26 27 28 29 30 31 32 57 58 59 60 61 62 63 64
node 7 size: 65536 MB
node 7 free: 43966 MB

CASE 1:
In 9.6.6 peak performance is achieved at 72 concurrent cleints TPS :
35554.573858 and in 10.1 at 72 clients TPS dips to 26882.828133 so
nearly 23% decrease in TPS.

CASE 2:
In 9.6.6 peak performance is achieved at 72 concurrent cleints TPS :
24861.074079 and in 10.1 at 72 clients TPS dips to 18372.565663 so
nearly 26% decrease in TPS.

Added "Postgresql_benchmarking_9.6vs10.ods" which gives more detailed
TPS numbers. And, TPS is median of 3 runs result.

I have not run bisect yet to find what has caused the issue.

--
Thanks and Regards
Mithun C Y
EnterpriseDB: http://www.enterprisedb.com