Small Datum: postgres

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Wednesday, December 10, 2025

The insert benchmark on a small server : Postgres 12.22 through 18.1

This has results for Postgres versions 12.22 through 18.1 with the Insert Benchmark on a small server.

Postgres continues to be boring in a good way. It is hard to find performance regressions.

tl;dr for a cached workload

performance has been stable from Postgres 12 through 18

tl;dr for an IO-bound workload

performance has mostly been stable
create index has been ~10% faster since Postgres 15
throughput for the write-only steps has been ~10% less since Postgres 15
throughput for the point-query steps (qp*) has been ~20% better since Postgres 13

Builds, configuration and hardware

I compiled Postgres from source using -O2 -fno-omit-frame-pointer for versions 12.22, 13.22, 13.23, 14.19, 14.20, 15.14, 15.15, 16.10, 16.11, 17.6, 17.7, 18.0 and 18.1.

The server is an ASUS ExpertCenter PN53 with and AMD Ryzen 7 7735HS CPU, 8 cores, SMT disabled, 32G of RAM. Storage is one NVMe device for the database using ext-4 with discard enabled. The OS is Ubuntu 24.04. More details on it are here.

For versions prior to 18, the config file is named conf.diff.cx10a_c8r32 and they are as similar as possible and here for versions 12, 13, 14, 15, 16 and 17.

For Postgres 18 I used 3 variations, which are here:

conf.diff.cx10b_c8r32

uses io_method='sync' to match Postgres 17 behavior

conf.diff.cx10c_c8r32

uses io_method='worker' and io_workers=16 to do async IO via a thread pool. I eventually learned that 16 is too large.

conf.diff.cx10d_c8r32

uses io_method='io_uring' to do async IO via io_uring

The Benchmark

The benchmark is explained here and is run with 1 client and 1 table. I repeated it with two workloads:

cached - the values for X, Y, Z are 30M, 40M, 10M
IO-bound - the values for X, Y, Z are 800M, 4M, 1M

The point query (qp100, qp500, qp1000) and range query (qr100, qr500, qr1000) steps are run for 1800 seconds each.

The benchmark steps are:

l.i0

insert X rows per table in PK order. The table has a PK index but no secondary indexes. There is one connection per client.

create 3 secondary indexes per table. There is one connection per client.

l.i1

use 2 connections/client. One inserts Y rows per table and the other does deletes at the same rate as the inserts. Each transaction modifies 50 rows (big transactions). This step is run for a fixed number of inserts, so the run time varies depending on the insert rate.

l.i2

like l.i1 but each transaction modifies 5 rows (small transactions) and Z rows are inserted and deleted per table.
Wait for S seconds after the step finishes to reduce variance during the read-write benchmark steps that follow. The value of S is a function of the table size.

qr100

use 3 connections/client. One does range queries and performance is reported for this. The second does does 100 inserts/s and the third does 100 deletes/s. The second and third are less busy than the first. The range queries use covering secondary indexes. If the target insert rate is not sustained then that is considered to be an SLA failure. If the target insert rate is sustained then the step does the same number of inserts for all systems tested. This step is frequently not IO-bound for the IO-bound workload.

qp100

like qr100 except uses point queries on the PK index

qr500

like qr100 but the insert and delete rates are increased from 100/s to 500/s

qp500

like qp100 but the insert and delete rates are increased from 100/s to 500/s

qr1000

like qr100 but the insert and delete rates are increased from 100/s to 1000/s

qp1000

like qp100 but the insert and delete rates are increased from 100/s to 1000/s

Results: overview

The performance reports are here for:

Cached

IO-bound

The summary sections from the performances report have 3 tables. The first shows absolute throughput by DBMS tested X benchmark step. The second has throughput relative to the version from the first row of the table. The third shows the background insert rate for benchmark steps with background inserts. The second table makes it easy to see how performance changes over time. The third table makes it easy to see which DBMS+configs failed to meet the SLA.

Below I use relative QPS to explain how performance changes. It is: (QPS for $me / QPS for $base) where $me is the result for some version $base is the result from Postgres 12.22.

When relative QPS is > 1.0 then performance improved over time. When it is < 1.0 then there are regressions. The Q in relative QPS measures:

insert/s for l.i0, l.i1, l.i2
indexed rows/s for l.x
range queries/s for qr100, qr500, qr1000
point queries/s for qp100, qp500, qp1000

This statement doesn't apply to this blog post, but I keep it here for copy/paste into future posts. Below I use colors to highlight the relative QPS values with red for <= 0.95, green for >= 1.05 and grey for values between 0.95 and 1.05.

Results: cached

The performance summaries are here for all versions and latest versions.

I focus on the latest versions. Throughput for 18.1 is within 2% of 12.22, with the exception of the l.i2 benchmark step. This is great news because it means that Postgres has avoided introducing new CPU overhead as they improve the DBMS. There is some noise from the l.i2 benchmark step and that doesn't surprise me because it is likely variance from two issues -- vacuum and get_actual_variable_range.

Results: IO-bound

The performance summaries are here for all versions and latest versions.

I focus on the latest versions.

throughput for the load step (l.i0) is 1% less in 18.1 vs 12.22
throughput for the index step (l.x) is 13% better in 18.1 vs 12.22
throughput for the write-only steps (l.i1, l.i2) is 11% and 12% less in 18.1 vs 12.22
throughput for the range-query steps (qr*) is 2%, 3% and 3% less in 18.1 vs 12.22
throughput for the point-query steps (qp*) is 22%, 23% and 23% better in 18.1 vs 12.22

The improvements for the index step arrived in Postgres 15.

The regressions for the write-only steps arrived in Postgres 15 and are likely from two issues -- vacuum and get_actual_variable_range.

The improvements for the point-query steps arrived in Postgres 13.

Saturday, November 29, 2025

Using sysbench to measure how Postgres performance changes over time, November 2025 edition

This has results for the sysbench benchmark on a small and big server for Postgres versions 12 through 18. Once again, Postgres is boring because I search for perf regressions and can't find any here. Results from MySQL are here and MySQL is not boring.

While I don't show the results here, I don't see regressions when comparing the latest point releases with their predecessors -- 13.22 vs 13.23, 14.19 vs 14.20, 15.14 vs 15.15, 16.10 vs 16.11, 17.6 vs 17.7 and 18.0 vs 18.1.

tl;dr

a few small regressions
many more small improvements
for write-heavy tests at high-concurrency there are many large improvements starting in PG 17

Builds, configuration and hardware

I compiled Postgres from source for versions 12.22, 13.22, 13.23, 14.19, 14.20, 15.14, 15.15, 16.10, 16.11, 17.6, 17.7, 18.0 and 18.1.

I used two servers:

small

an ASUS ExpertCenter PN53 with AMD Ryzen 7735HS CPU, 32G of RAM, 8 cores with AMD SMT disabled, Ubuntu 24.04 and an NVMe device with ext4 and discard enabled.

an ax162s from Hetzner with an AMD EPYC 9454P 48-Core Processor with SMT disabled
2 Intel D7-P5520 NVMe storage devices with RAID 1 (3.8T each) using ext4
128G RAM
Ubuntu 22.04 running the non-HWE kernel (5.5.0-118-generic)

Configuration files for the small server

Configuration files are here for Postgres versions 12, 13, 14, 15, 16 and 17.
For Postgres 18 I used io_method=sync and the configuration file is here.

Configuration files for the big server

Configuration files are here for Postgres versions 12, 13, 14, 15, 16 and 17.
For Postgres 18 I used io_method=sync and the configuration file is here.

Benchmark

I used sysbench and my usage is explained here. I now run 32 of the 42 microbenchmarks listed in that blog post. Most test only one type of SQL statement. Benchmarks are run with the database cached by InnoDB.

The read-heavy microbenchmarks are run for 600 seconds and the write-heavy for 900 seconds. On the small server the benchmark is run with 1 client and 1 table with 50M rows. On the big server the benchmark is run with 12 clients and 8 tables with 10M rows per table.

The purpose is to search for regressions from new CPU overhead and mutex contention. I use the small server with low concurrency to find regressions from new CPU overheads and then larger servers with high concurrency to find regressions from new CPU overheads and mutex contention.

Results

The microbenchmarks are split into 4 groups -- 1 for point queries, 2 for range queries, 1 for writes. For the range query microbenchmarks, part 1 has queries that don't do aggregation while part 2 has queries that do aggregation.

I provide charts below with relative QPS. The relative QPS is the following:

(QPS for some version) / (QPS for Postgres 12.22)

When the relative QPS is > 1 then some version is faster than Postgres 12.12. When it is < 1 then there might be a regression. When the relative QPS is 1.2 then some version is about 20% faster than Postgres 12.22.

Values from iostat and vmstat divided by QPS are here for the small server and the big server. These can help to explain why something is faster or slower because it shows how much HW is used per request, including CPU overhead per operation (cpu/o) and context switches per operation (cs/o) which are often a proxy for mutex contention.

The spreadsheet and charts are here and in some cases are easier to read than the charts below. Converting the Google Sheets charts to PNG files does the wrong thing for some of the test names listed at the bottom of the charts below.

Results: point queries

This is from the small server.

a large improvement arrived in Postgres 17 for the hot-points test
otherwise results have been stable from 12.22 through 18.1

This is from the big server.

a large improvement arrived in Postgres 17 for the hot-points test
otherwise results have been stable from 12.22 through 18.1

Results: range queries without aggregation

This is from the small server.

there are small improvements for the scan test
otherwise results have been stable from 12.22 through 18.1

This is from the big server.

there are small improvements for the scan test
otherwise results have been stable from 12.22 through 18.1

Results: range queries with aggregation

This is from the small server.

there are small improvements for a few tests
otherwise results have been stable from 12.22 through 18.1

This is from the big server.

there might be small regressions for a few tests
otherwise results have been stable from 12.22 through 18.1

Results: writes

This is from the small server.

there are small improvements for most tests
otherwise results have been stable from 12.22 through 18.1

This is from the big server.

there are large improvements for half of the tests
otherwise results have been stable from 12.22 through 18.1

From vmstat results for update-index the per-operation CPU overhead and context switch rate are much smaller starting in Postgres 17.7. The CPU overhead is about 70% of what it was in 16.11 and the context switch rate is about 50% of the rate for 16.11. Note that context switch rates are often a proxy for mutex contention.

Saturday, November 22, 2025

Challenges compiling old C++ code on modern Linux

I often compile old versions of MySQL, MariaDB, Postgres and RocksDB in my search for performance regressions. Compiling is easy with Postgres as they do a great job at avoiding compilation warnings and I never encounter broken builds. Certainly the community gets the credit for this, but I suspect their task is easier because they use C. This started as a LinkedIn post.

I expect people to disagree, and I am far from a C++ expert, but here goes ...

tl;dr - if you maintain widely used header files (widely used by C++ projects) consider not removing that include that you don't really need (like <cstdint>) because such removal is likely to break builds for older releases of projects that use your include.

I have more trouble compiling older releases of C++ projects. For MySQL I have a directory in github that includes patches that must be applied. And for MySQL I have to patch all 5.6 versions, 5.7 versions up to 5.7.33 and 8.0 versions up to 8.0.23. The most common reason for the patch is missing C++ includes (like <cstdint>).

For RocksDB with gcc I don't have to patch files but I need to use gcc-11 for RocksDB 6.x and gcc-12 for RocksDB 7.x.

For RocksDB with clang I don't have to patch files for RocksDB 8.x, 9.x and 10.x while I do have to patch 6.x and 7.x. For RocksDB 7.10 I need to edit two files to add <cstdint>. The files are:

table/block_based/data_block_hash_index.h
util/string_util.h

All of this is true for Ubuntu 24.04 with clang 18.1.3 and gcc 13.3.0.

One more detail, for my future self, the command line I use to compile RocksDB with clang is one of the following:

Rather than remember which of V= and VERBOSE= that I need, I just use both
I get errors if I don't define AR and RANLIB when using clang
While clang-18 installs clang and clang++ binaries, to get the llvm variants of ar and ranlib I need to use llvm-ar-18 and llvm-ranlib-18 rather than llvm-ar and llvm-ranlib

# without link-time optimization
AR=llvm-ar-18 RANLIB=llvm-ranlib-18 \
CC=clang CXX=clang++ \
make \
DISABLE_WARNING_AS_ERROR=1 DEBUG_LEVEL=0 V=1 VERBOSE=1 -j... \

static_lib db_bench

# with link-time optimization

AR=llvm-ar-18 RANLIB=llvm-ranlib-18 \
CC=clang CXX=clang++ \
make USE_LTO=1 \
DISABLE_WARNING_AS_ERROR=1 DEBUG_LEVEL=0 V=1 VERBOSE=1 -j... \
static_lib db_bench

Monday, October 13, 2025

Postgres 18.0 vs sysbench on a 32-core server

This is yet another great result for Postgres 18.0 vs sysbench. This time I used a 32-core server. Results for a 24-core server are here. The goal for this benchmark is to check for regressions from new CPU overhead and mutex contention.

I repeated the benchmark twice because I had some uncertainty about platform variance (HW and SW) on the first run.

tl;dr, from Postgres 17.6 to 18.0

There might be regressions from 17.6 to 18.0 but they are small (usually <= 3%)

tl;dr, from Postgres 12.22 through 18.0

the hot-points test is almost 2X faster starting in 17.6
scan is ~1.2X faster starting in 14.19
all write tests are much faster staring in 17.6

Builds, configuration and hardware

I compiled Postgres from source for versions 12.22, 13.22, 14.19, 15.14, 16.10, 17.6, and 18.0.

The server is a Dell Precision 7865 Tower Workstation with 1 socket, 128G RAM and an AMD Ryzen Threadripper PRO 5975WX with 32-Cores. The OS is Ubuntu 24.04 and storage is a 2TB m.2 SSD with ext-4 and discard enabled.

Prior to 18.0, the configuration file was named conf.diff.cx10a_c32r128 and is here for 12.22, 13.22, 14.19, 15.14, 16.10 and 17.6.

For 18.0 I tried 3 configuration files:

conf.diff.cx10b_c32r128 (x10b) - uses io_method=sync
conf.diff.cx10c_c32r128 (x10c) - uses io_method=worker
conf.diff.cx10d_c32r128 (x10d) - uses io_method=io_uring

Benchmark

I used sysbench and my usage is explained here. To save time I only run 32 of the 42 microbenchmarks

and most test only 1 type of SQL statement. Benchmarks are run with the database cached by Postgres.

The read-heavy microbenchmarks run for 600 seconds and the write-heavy for 900 seconds.

The benchmark is run with 24 clients and 8 tables with 10M rows per table. The purpose is to search for regressions from new CPU overhead and mutex contention.

I ran the benchmark twice. In the first run, there was several weeks between getting results for the older Postgres releases and Postgres 18.0 so I am less certain about variance from the hardware and softare. One concern is changes in daily temperature because I don't have a climate-controlled server room. Another concern is changes from updating my OS install.

In the second run, all results were collected within 7 days and I am less concerned about variance there.

Results

I provide charts below with relative QPS. The relative QPS is the following:

(QPS for some version) / (QPS for base version)

When the relative QPS is > 1 then some version is faster than base version. When it is < 1 then there might be a regression. Values from iostat and vmstat divided by QPS are also provided here. These can help to explain why something is faster or slower because it shows how much HW is used per request.

I present results for:

versions 12 through 18 using 12.22 as the base version
versions 17.6 and 18.0 using 17.6 as the base version

Results: Postgres 17.6 and 18.0

All files are here.

Results per microbenchmark from vmstat and iostat are here for the first and second run.

Some comments:

18.0 looks better relative to 17.6 in the second run and I explain my uncertainty about the first run above
But I am skeptical about the great result for 18.0 on the full scan test (scan_range=100) in the second run. That might be variance induced by vacuum.
There might be regressions from 17.6 to 18.0 but they are small (usually <= 3%)
The small regression in read-only_range=10 might be from new optimizer overhead, because it doesn't reproduce when the length of the range query is increased -- see read-only_range=100 and read-only_range=10000.

Relative to: 17.6

col-1 : 18.0 with the x10b config that uses io_method=sync

col-2 : 18.0 with the x10c config that uses io_method=worker

col-3 : 18.0 with the x10d config that uses io_method=io_uring

col-1 col-2 col-3 point queries, first run

0.97 0.99 0.94 hot-points_range=100

0.97 0.98 0.96 point-query_range=100

1.00 0.99 0.99 points-covered-pk_range=100

0.99 1.00 1.00 points-covered-si_range=100

0.98 0.99 0.98 points-notcovered-pk_range=100

0.99 0.99 0.99 points-notcovered-si_range=100

1.00 1.00 0.99 random-points_range=1000

0.98 0.98 0.98 random-points_range=100

0.99 0.98 0.99 random-points_range=10

col-1 col-2 col-3 point queries, second run

0.98 1.00 0.99 hot-points_range=100

1.00 1.00 0.99 point-query_range=100

1.01 1.01 1.01 points-covered-pk_range=100

1.00 1.01 1.00 points-covered-si_range=100

1.00 0.98 1.00 points-notcovered-pk_range=100

1.00 1.00 1.01 points-notcovered-si_range=100

1.00 1.01 1.01 random-points_range=1000

1.00 0.99 1.01 random-points_range=100

0.99 0.99 1.00 random-points_range=10

col-1 col-2 col-3 range queries without aggregation, first run

0.97 0.98 0.95 range-covered-pk_range=100

0.97 0.97 0.94 range-covered-si_range=100

0.98 0.98 0.97 range-notcovered-pk_range=100

0.99 0.99 0.98 range-notcovered-si_range=100

0.97 0.99 0.96 scan_range=100

col-1 col-2 col-3 range queries without aggregation, second run

0.99 0.99 0.98 range-covered-pk_range=100

0.99 0.99 0.99 range-covered-si_range=100

0.98 0.99 0.98 range-notcovered-pk_range=100

0.99 1.00 1.00 range-notcovered-si_range=100

1.24 1.24 1.22 scan_range=100

col-1 col-2 col-3 range queries with aggregation, first run

0.99 1.00 1.00 read-only-count_range=1000

1.01 1.01 1.01 read-only-distinct_range=1000

1.01 1.01 1.00 read-only-order_range=1000

1.04 1.04 1.04 read-only_range=10000

0.99 0.99 0.98 read-only_range=100

0.97 0.98 0.97 read-only_range=10

0.99 0.98 0.98 read-only-simple_range=1000

0.99 0.99 0.99 read-only-sum_range=1000

col-1 col-2 col-3 range queries with aggregation, second run

0.99 1.00 1.00 read-only-count_range=1000

1.01 1.01 1.00 read-only-distinct_range=1000

0.99 0.99 1.00 read-only-order_range=1000

1.02 1.03 1.03 read-only_range=10000

0.99 0.99 0.99 read-only_range=100

0.99 0.99 0.98 read-only_range=10

0.99 1.00 1.01 read-only-simple_range=1000

1.00 1.00 1.00 read-only-sum_range=1000

col-1 col-2 col-3 writes, first run

0.99 0.98 0.96 delete_range=100

0.99 0.96 0.98 insert_range=100

1.00 0.99 0.98 read-write_range=100

0.99 0.98 0.98 read-write_range=10

1.00 0.99 1.00 update-index_range=100

1.03 0.95 1.01 update-inlist_range=100

0.99 0.99 1.00 update-nonindex_range=100

1.00 1.00 1.01 update-one_range=100

0.98 0.99 1.00 update-zipf_range=100

0.97 0.97 0.99 write-only_range=10000

col-1 col-2 col-3 writes, second run

0.97 0.97 0.98 delete_range=100

0.99 0.99 1.00 insert_range=100

0.99 0.99 0.98 read-write_range=100

0.98 0.98 0.98 read-write_range=10

0.97 0.98 0.97 update-index_range=100

0.98 0.99 1.04 update-inlist_range=100

0.98 0.99 0.98 update-nonindex_range=100

0.99 0.99 0.98 update-one_range=100

0.98 0.99 0.98 update-zipf_range=100

0.99 0.97 0.95 write-only_range=10000

Results: Postgres 12 to 18

All files are here.

Results per microbenchmark from vmstat and iostat are here for the first and second run.

The data below with a larger font is here.

Some comments:

the hot-points test is almost 2X faster starting in 17.6
scan is ~1.2X faster starting in 14.19
all write tests are much faster staring in 17.6

Relative to: 12.22

col-1 : 13.22

col-2 : 14.19

col-3 : 15.14

col-4 : 16.10

col-5 : 17.6

col-6 : 18.0 with the x10b config

col-7 : 18.0 with the x10c config

col-8 : 18.0 with the x10d config

col-1 col-2 col-3 col-4 col-5 col-6 col-7 col-8 point queries, first run

1.02 1.00 1.01 1.00 1.94 1.87 1.91 1.82 hot-points_range=100

1.01 1.02 1.02 1.00 1.02 0.99 1.00 0.98 point-query_range=100

1.02 1.02 1.01 1.03 1.01 1.01 1.00 1.00 points-covered-pk_range=100

1.01 1.04 1.03 1.05 1.03 1.02 1.03 1.03 points-covered-si_range=100

1.01 1.01 1.01 1.02 1.02 1.00 1.00 1.00 points-notcovered-pk_range=100

1.00 1.03 1.02 1.03 1.02 1.01 1.01 1.02 points-notcovered-si_range=100

1.01 1.02 1.02 1.03 1.00 1.00 1.00 0.99 random-points_range=1000

1.01 1.02 1.02 1.02 1.02 1.00 1.00 1.00 random-points_range=100

1.02 1.03 1.02 1.02 1.01 1.00 1.00 1.00 random-points_range=10

col-1 col-2 col-3 col-4 col-5 col-6 col-7 col-8 point queries, second run

1.00 0.98 0.99 1.00 1.94 1.90 1.93 1.92 hot-points_range=100

1.00 1.01 1.02 1.03 1.03 1.02 1.02 1.02 point-query_range=100

1.02 1.01 1.00 1.04 0.99 1.00 1.00 0.99 points-covered-pk_range=100

1.01 1.04 1.03 1.07 1.03 1.03 1.05 1.04 points-covered-si_range=100

1.01 1.02 1.03 1.04 1.01 1.00 0.99 1.01 points-notcovered-pk_range=100

1.02 1.05 1.05 1.05 1.03 1.03 1.03 1.04 points-notcovered-si_range=100

1.01 1.02 1.03 1.03 0.99 0.99 1.00 1.00 random-points_range=1000

1.02 1.02 1.03 1.04 1.01 1.01 1.00 1.01 random-points_range=100

1.02 1.02 1.02 1.03 1.02 1.01 1.01 1.02 random-points_range=10

col-1 col-2 col-3 col-4 col-5 col-6 col-7 col-8 range queries without aggregation, first run

1.00 1.02 1.02 1.01 1.00 0.97 0.98 0.95 range-covered-pk_range=100

1.00 1.02 1.02 1.01 1.00 0.97 0.97 0.94 range-covered-si_range=100

1.01 1.00 1.00 1.00 0.99 0.97 0.97 0.97 range-notcovered-pk_range=100

0.99 1.00 1.00 0.99 1.01 1.00 1.00 0.99 range-notcovered-si_range=100

0.98 1.24 1.11 1.13 1.16 1.12 1.14 1.11 scan_range=100

col-1 col-2 col-3 col-4 col-5 col-6 col-7 col-8 range queries without aggregation, second run

1.01 1.02 1.02 1.02 1.01 1.00 1.00 0.99 range-covered-pk_range=100

1.01 1.03 1.02 1.02 1.01 1.00 1.01 1.00 range-covered-si_range=100

1.00 0.99 1.00 1.00 0.99 0.97 0.98 0.98 range-notcovered-pk_range=100

1.00 1.00 1.00 0.98 1.01 1.00 1.01 1.01 range-notcovered-si_range=100

1.00 1.27 1.15 1.15 0.97 1.20 1.20 1.18 scan_range=100

col-1 col-2 col-3 col-4 col-5 col-6 col-7 col-8 range queries with aggregation, first run

1.02 1.00 1.00 1.01 0.97 0.96 0.97 0.97 read-only-count_range=1000

1.00 1.00 1.02 1.02 0.98 0.99 0.99 0.99 read-only-distinct_range=1000

1.01 1.00 1.03 1.03 1.00 1.01 1.01 1.01 read-only-order_range=1000

1.00 0.98 1.00 1.06 0.95 0.99 0.99 0.99 read-only_range=10000

1.00 1.00 1.00 1.00 1.00 0.98 0.98 0.98 read-only_range=100

1.00 1.01 1.01 1.00 1.01 0.98 0.99 0.98 read-only_range=10

1.01 1.00 1.02 1.01 1.00 0.99 0.98 0.98 read-only-simple_range=1000

1.00 1.00 1.01 1.00 0.99 0.98 0.98 0.98 read-only-sum_range=1000

col-1 col-2 col-3 col-4 col-5 col-6 col-7 col-8 range queries with aggregation, second run

1.03 1.02 1.02 1.03 0.97 0.97 0.97 0.98 read-only-count_range=1000

1.00 0.99 1.02 1.02 0.98 0.99 0.99 0.99 read-only-distinct_range=1000

1.00 0.99 1.02 1.04 1.02 1.01 1.01 1.02 read-only-order_range=1000

1.01 1.03 1.03 1.06 0.97 0.99 0.99 0.99 read-only_range=10000

0.99 1.00 1.00 1.01 1.00 0.99 0.99 0.99 read-only_range=100

0.99 1.00 1.00 1.00 1.01 0.99 1.00 0.99 read-only_range=10

1.00 0.99 1.01 1.00 0.99 0.98 0.98 0.99 read-only-simple_range=1000

1.00 1.00 1.01 1.01 0.99 0.98 0.98 0.98 read-only-sum_range=1000

col-1 col-2 col-3 col-4 col-5 col-6 col-7 col-8 writes, first run

1.00 1.08 1.08 1.05 1.25 1.24 1.23 1.20 delete_range=100

1.01 1.05 1.04 1.03 1.07 1.06 1.02 1.05 insert_range=100

1.00 1.06 1.07 1.07 1.10 1.09 1.08 1.07 read-write_range=100

1.00 1.07 1.08 1.07 1.13 1.13 1.11 1.11 read-write_range=10

0.99 1.04 1.04 0.90 1.43 1.43 1.41 1.43 update-index_range=100

1.00 1.09 1.08 1.08 1.11 1.15 1.06 1.12 update-inlist_range=100

1.00 1.05 1.05 1.04 1.35 1.34 1.34 1.35 update-nonindex_range=100

1.02 0.95 0.96 0.93 1.19 1.19 1.19 1.20 update-one_range=100

1.00 1.05 1.08 1.07 1.23 1.21 1.22 1.23 update-zipf_range=100

1.01 1.06 1.05 1.01 1.25 1.22 1.20 1.24 write-only_range=10000

col-1 col-2 col-3 col-4 col-5 col-6 col-7 col-8 writes, second run

1.00 1.06 1.07 1.07 1.26 1.23 1.23 1.24 delete_range=100

1.03 1.07 1.05 1.05 1.09 1.07 1.08 1.09 insert_range=100

1.01 1.07 1.08 1.07 1.11 1.10 1.10 1.09 read-write_range=100

0.99 1.04 1.06 1.07 1.13 1.11 1.11 1.12 read-write_range=10

0.99 1.02 1.04 0.87 1.44 1.40 1.41 1.40 update-index_range=100

1.00 1.11 1.12 1.09 1.17 1.14 1.16 1.22 update-inlist_range=100

1.01 1.04 1.06 1.03 1.36 1.33 1.35 1.34 update-nonindex_range=100

1.01 0.95 0.98 0.94 1.22 1.21 1.21 1.20 update-one_range=100

0.99 1.05 1.07 1.07 1.24 1.21 1.22 1.21 update-zipf_range=100

1.02 1.06 1.06 1.02 1.27 1.25 1.23 1.21 write-only_range=10000

Sunday, October 5, 2025

Measuring scaleup for Postgres 18.0 with sysbench

This post has results to measure scaleup for Postgres 18.0 on a 48-core server.

tl;dr

Postgres continues to be boring (in a good way)
Results are mostly excellent
A few of the range query tests have a scaleup that is less than great but I need time to debug

Builds, Configuration & Hardware

The server has an AMD EPYC 9454P 48-Core Processor with AMD SMT disabled, 128G of RAM and SW RAID 0 with 2 NVMe devices. The OS is Ubuntu 22.04.

I compiled Postgres 18.0 from source and the configuration file is here.

Benchmark

I used sysbench and my usage is explained here. To save time I only run 32 of the 42 microbenchmarks

and most test only 1 type of SQL statement. Benchmarks are run with the database cached by Postgres. Each microbenchmark is run for 300 seconds.

The benchmark is run with 1, 2, 4, 8, 12, 16, 20, 24, 32, 40 and 48 clients. The purpose is to determine how well Postgres scales up. All tests use 8 tables with 10M rows per table.

Results

I still use relative QPS here, but in a different way. The relative QPS here is:

(QPS at X clients) / (QPS at 1 client)

The goal is to determine scaleup efficiency for Postgres. When the relative QPS at X clients is a value near X, then things are great. But sometimes things aren't great and the relative QPS is much less than X. One issue is data contention for some of the write-heavy microbenchmarks. Another issue is mutex and rw-lock contention.

Perf debugging via vmstat and iostat

I use normalized results from vmstat and iostat to help explain why things aren't as fast as expected. By normalized I mean I divide the average values from vmstat and iostat by QPS to see things like how much CPU is used per query or how many context switches occur per write. And note that a high context switch rate is often a sign of mutex contention.

Those results are here but can be difficult to read.

Charts: point queries

The spreadsheet with all of the results is here.

While results aren't perfect, they are excellent. Perfect results would be to get a scaleup of 48 at 48 clients and here the result is between 40 and 42 in most tests. The worst-case is for hot-points where the scaleup is 32.57 at 48 clients. Note that the hot-points test has the most data contention of the point-query tests, as all queries fetch the same rows.

From the vmstat metrics (see here) I don't see an increase in mutex contention (more context switches, see the cs/o column) but I do see an increase in CPU (cpu/o). When compared to a test that has better scaleup, like points-covered-pk, there I also don't see an increase in mutex contention and do see an increase in CPU overhead (see cpu/o) but the CPU increase is smaller (see here).

Charts: range queries without aggregation

The spreadsheet with all of the results is here.

The results again are great, but not perfect. The worst case is for range-notcovered-pk where the scaleup is 32.92 at 48 clients. The base case is for scan where the scaleup is 46.56 at 48 clients.

From the vmstat metrics for range-notcovered-pk I don't see any obvious problems. The CPU overhead (cpu/o, CPU per query) increases by 1.08 (about 8%) from 1 to 48 clients while the context switches per query (cs/o) decreases (see here).

Charts: range queries with aggregation

The spreadsheet with all of the results is here.

Results for range queries with aggregation are worse than for range queries without aggregation. I hope to try and explain that later. A perfect result is scaleup equal to 48. Here, 3 of 8 tests have scaleup less than 3, 4 have scaleup between 30 and 40, and the best case is read-only_range=10 with a scaleup of 43.35.

The worst-case was read-only-count with a scaleup of 21.38. From the vmstat metrics I see that at CPU overhead (cpu/o, CPU per query) increases by 2.08 at 48 clients vs 1 client while context switches per query (cs/o) decrease (see here). I am curious about that CPU increase as isn't as bad for the other range query tests, for example see here where it is no larger than 1.54. The query for read-only-count is here.

Later I hope to explain why read-only-count, read-only-simple and read-only-sum don't do better.

Charts: writes

The spreadsheet with all of the results is here.

The worst-case is update-one where scaleup is 2.86 at 48 clients. The bad result is expected as having many concurrent clients update the same row is an anti-pattern with Postgres. The scaleup for Postgres on that test is a lot worse than for MySQL where it was ~8 with InnoDB. But I am not here for Postgres vs InnoDB arguments.

Excluding the tests that mix reads and writes (read-write-*) the scaleup is between 13 and 21. This is far from great but isn't horrible. I run with fsync-on-commit disabled which highlights problems but is less realistic. So for now I am happy with this results.

Monday, September 29, 2025

Postgres 18.0 vs sysbench on a 24-core, 2-socket server

This post has results from sysbench run at higher concurrency for Postgres versions 12 through 18 on a server with 24 cores and 2 sockets. My previous post had results for sysbench run with low concurrency. The goal is to search for regressions from new CPU overhead and mutex contention.

tl;dr, from Postgres 17.6 to 18.0

For most microbenchmarks Postgres 18.0 is between 1% and 3% slower than 17.6
The root cause might be new CPU overhead. It will take more time to gain confidence in results like this. On other servers with sysbench run at low concurrency I only see regressions for some of the range-query microbenchmarks. Here I see them for point-query and writes.

tl;dr, from Postgres 12.22 through 18.0

For point queries Postgres 18.0 is usually about 5% faster than 12.22
For range queries Postgres 18.0 is usually as fast as 12.22
For writes Postgres 18.0 is much faster than 12.22

Builds, configuration and hardware

I compiled Postgres from source for versions 12.22, 13.22, 14.19, 15.14, 16.10, 17.6, and 18.0.

The server is a SuperMicro SuperWorkstation 7049A-T with 2 sockets, 12 cores/socket, 64G RAM. The CPU is Intel Xeon Silver 4214R CPU @ 2.40GHz. It runs Ubuntu 24.04. Storage is a 1TB m.2 NVMe device with ext-4 and discard enabled.

Prior to 18.0, the configuration file was named conf.diff.cx10a_c24r64 and is here for 12.22, 13.22, 14.19, 15.14, 16.10 and 17.6.

For 18.0 I tried 3 configuration files:

conf.diff.cx10b_c24r64 (x10b) - uses io_method=sync
conf.diff.cx10c_c24r64 (x10c) - uses io_method=worker
conf.diff.cx10d_c24r64 (x10d) - uses io_method=io_uring

Benchmark

I used sysbench and my usage is explained here. To save time I only run 32 of the 42 microbenchmarks

and most test only 1 type of SQL statement. Benchmarks are run with the database cached by Postgres.

The read-heavy microbenchmarks run for 600 seconds and the write-heavy for 900 seconds.

The benchmark is run with 16 clients and 8 tables with 10M rows per table. The purpose is to search for regressions from new CPU overhead and mutex contention.

Results

I provide charts below with relative QPS. The relative QPS is the following:

(QPS for some version) / (QPS for base version)

versions 12 through 18 using 12.22 as the base version
versions 17.6 and 18.0 using 17.6 as the base version

Results: Postgres 17.6 and 18.0

Results per microbenchmark from vmstat and iostat are here.

For point queries, 18.0 often gets between 1% and 3% less QPS than 17.6 and the root cause might be new CPU overhead. See the cpu/o column (CPU per query) in the vmstat metrics here for the random-points microbenchmarks.

For range queries, 18.0 often gets between 1% and 3% less QPS than 17.6 and the root cause might be new CPU overhead. See the cpu/o column (CPU per query) in the vmstat metrics here for the read-only_range=X microbenchmarks.

For writes queries, 18.0 often gets between 1% and 2% less QPS than 17.6 and the root cause might be new CPU overhead. I ignore the write-heavy microbenchmarks that also do queries as the regressions for them might be from the queries. See the cpu/o column (CPU per query) in the vmstat metrics here for the update-index microbenchmark.

Relative to: 17.6

col-1 : 18.0 with the x10b config

col-2 : 18.0 with the x10c config

col-3 : 18.0 with the x10d config

col-1 col-2 col-3 point queries

1.00 0.99 1.00 hot-points_range=100

0.99 0.98 1.00 point-query_range=100

0.98 0.99 0.99 points-covered-pk_range=100

0.99 0.99 0.98 points-covered-si_range=100

0.97 0.99 0.98 points-notcovered-pk_range=100

0.98 0.99 0.97 points-notcovered-si_range=100

0.98 0.99 0.98 random-points_range=1000

0.97 0.99 0.98 random-points_range=100

0.99 0.99 0.98 random-points_range=10

col-1 col-2 col-3 range queries without aggregation

0.98 0.98 0.99 range-covered-pk_range=100

0.98 0.98 0.98 range-covered-si_range=100

0.98 0.99 0.98 range-notcovered-pk_range=100

1.00 1.02 0.99 range-notcovered-si_range=100

1.01 1.01 1.01 scan_range=100

col-1 col-2 col-3 range queries with aggregation

0.99 1.00 0.98 read-only-count_range=1000

0.98 0.98 0.98 read-only-distinct_range=1000

0.97 0.97 0.96 read-only-order_range=1000

0.97 0.98 0.97 read-only_range=10000

0.98 0.99 0.98 read-only_range=100

0.99 0.99 0.99 read-only_range=10

0.98 0.99 0.99 read-only-simple_range=1000

0.98 1.00 0.98 read-only-sum_range=1000

col-1 col-2 col-3 writes

0.99 0.99 0.99 delete_range=100

0.99 0.99 0.99 insert_range=100

0.98 0.98 0.98 read-write_range=100

0.99 1.00 0.99 read-write_range=10

0.99 0.98 0.97 update-index_range=100

0.99 0.99 1.00 update-inlist_range=100

1.00 0.97 0.99 update-nonindex_range=100

0.97 1.00 0.98 update-one_range=100

1.00 0.99 1.01 update-zipf_range=100

0.98 0.98 0.97 write-only_range=10000

Results: Postgres 12 to 18

For the Postgres 18.0 results in col-6, the result is in green when relative QPS is >= 1.05 and in yellow when relative QPS is <= 0.98. Yellow indicates a possible regression.

Results per microbenchmark from vmstat and iostat are here.

Relative to: 12.22

col-1 : 13.22

col-2 : 14.19

col-3 : 15.14

col-4 : 16.10

col-5 : 17.6

col-6 : 18.0 with the x10b config

col-1 col-2 col-3 col-4 col-5 col-6 point queries

0.98 0.96 0.99 0.98 2.13 2.13 hot-points_range=100

1.00 1.02 1.01 1.02 1.03 1.01 point-query_range=100

0.99 1.05 1.05 1.08 1.07 1.05 points-covered-pk_range=100

0.99 1.08 1.05 1.07 1.07 1.05 points-covered-si_range=100

0.99 1.04 1.05 1.06 1.07 1.05 points-notcovered-pk_range=100

0.99 1.05 1.04 1.05 1.06 1.04 points-notcovered-si_range=100

0.98 1.03 1.04 1.06 1.06 1.04 random-points_range=1000

0.98 1.04 1.05 1.07 1.07 1.05 random-points_range=100

0.99 1.02 1.03 1.05 1.05 1.04 random-points_range=10

col-1 col-2 col-3 col-4 col-5 col-6 range queries without aggregation

1.02 1.04 1.03 1.04 1.03 1.01 range-covered-pk_range=100

1.05 1.07 1.06 1.06 1.06 1.05 range-covered-si_range=100

0.99 1.00 1.00 1.00 1.01 0.98 range-notcovered-pk_range=100

0.97 0.99 1.00 1.01 1.01 1.01 range-notcovered-si_range=100

0.86 1.06 1.08 1.17 1.18 1.20 scan_range=100

col-1 col-2 col-3 col-4 col-5 col-6 range queries with aggregation

0.98 0.97 0.97 1.00 0.98 0.97 read-only-count_range=1000

0.99 0.99 1.02 1.02 1.01 0.99 read-only-distinct_range=1000

1.00 0.99 1.02 1.05 1.05 1.02 read-only-order_range=1000

0.99 0.99 1.04 1.07 1.09 1.06 read-only_range=10000

0.99 1.00 1.00 1.01 1.02 0.99 read-only_range=100

1.00 1.00 1.00 1.01 1.01 1.00 read-only_range=10

0.99 0.99 1.00 1.01 1.01 0.99 read-only-simple_range=1000

0.98 0.99 0.99 1.00 1.00 0.98 read-only-sum_range=1000

col-1 col-2 col-3 col-4 col-5 col-6 writes

0.98 1.09 1.09 1.04 1.29 1.27 delete_range=100

0.99 1.03 1.02 1.03 1.08 1.07 insert_range=100

1.00 1.03 1.04 1.05 1.07 1.05 read-write_range=100

1.01 1.09 1.09 1.09 1.15 1.14 read-write_range=10

1.00 1.04 1.03 0.86 1.44 1.42 update-index_range=100

1.01 1.11 1.11 1.12 1.13 1.12 update-inlist_range=100

0.99 1.04 1.06 1.05 1.25 1.25 update-nonindex_range=100

1.05 0.92 0.90 0.84 1.18 1.15 update-one_range=100

0.98 1.04 1.03 1.01 1.26 1.26 update-zipf_range=100

1.02 1.05 1.10 1.09 1.21 1.18 write-only_range=10000