Hi,
On 2024-04-06 14:34:17 +1300, David Rowley wrote:
> I don't see any issues with v5, so based on the performance numbers
> shown on this thread for the latest patch, it would make sense to push
> it. The problem is, I just can't recreate the performance numbers.
>
> I've tried both on my AMD 3990x machine and an Apple M2 with a script
> similar to the test.sh from above. I mostly just stripped out the
> buffer size stuff and adjusted the timing code to something that would
> work with mac.
I think there are a few issues with the test script leading to not seeing a
gain:
1) I think using the textual protocol, with the text datatype, will make it
harder to spot differences. That's a lot of overhead.
2) Afaict the test is connecting over the unix socket, I think we expect
bigger wins for tcp
3) Particularly the larger string is bottlenecked due to pglz compression in
toast.
Where I had noticed the overhead of the current approach badly, was streaming
out basebackups. Which is all binary, of course.
I added WITH BINARY, SET STORAGE EXTERNAL and tested both unix socket and
localhost. I also reduced row counts and iteration counts, because I am
impatient, and I don't think it matters much here. Attached the modified
version.
On a dual xeon Gold 5215, turbo boost disabled, server pinned to one core,
script pinned to another:
unix:
master:
Run 100 100 1000000: 0.058482377
Run 1024 10240 100000: 0.120909810
Run 1024 1048576 2000: 0.153027916
Run 1048576 1048576 1000: 0.154953512
v5:
Run 100 100 1000000: 0.058760126
Run 1024 10240 100000: 0.118831396
Run 1024 1048576 2000: 0.124282503
Run 1048576 1048576 1000: 0.123894962
localhost:
master:
Run 100 100 1000000: 0.067088000
Run 1024 10240 100000: 0.170894273
Run 1024 1048576 2000: 0.230346632
Run 1048576 1048576 1000: 0.230336078
v5:
Run 100 100 1000000: 0.067144036
Run 1024 10240 100000: 0.167950948
Run 1024 1048576 2000: 0.135167027
Run 1048576 1048576 1000: 0.135347867
The perf difference for 1MB via TCP is really impressive.
The small regression for small results is still kinda visible, I haven't yet
tested the patch downthread.
Greetings,
Andres Freund
#!/bin/bash
set -e
dbname=postgres
port=5440
host=/tmp
host=localhost
test_cases=(
"100 100 1000000" # only 100 bytes
"1024 10240 100000" # 1Kb and 10Kb
"1024 1048576 2000" # 1Kb and 1Mb
"1048576 1048576 1000" # all 1Mb
)
insert_rows(){
psql -d $dbname -p $port -h $host -c "
DO \$\$
DECLARE
counter INT;
BEGIN
FOR counter IN 1..$3 LOOP
IF counter % 2 = 1 THEN
INSERT INTO test_table VALUES (repeat('a', $1)::text);
ELSE
INSERT INTO test_table VALUES (repeat('b', $2)::text);
END IF;
END LOOP;
END \$\$;
" > /dev/null
}
psql -d $dbname -p $port -c "CREATE EXTENSION IF NOT EXISTS pg_prewarm;" >
/dev/null
for case in "${test_cases[@]}"
do
psql -d $dbname -p $port -h $host -c "DROP TABLE IF EXISTS test_table;"
> /dev/null
psql -d $dbname -p $port -h $host -c "CREATE UNLOGGED TABLE
test_table(data text not null);" > /dev/null
psql -d $dbname -p $port -h $host -c "ALTER TABLE test_table ALTER
data SET STORAGE EXTERNAL;" > /dev/null
insert_rows $case
psql -d $dbname -p $port -h $host -c "select
pg_prewarm('test_table');" > /dev/null
echo -n "Run $case: "
elapsed_time=0
for a in {1..5}
do
start_time=$(perl -MTime::HiRes=time -e 'printf "%.9f\n", time')
psql -d $dbname -p $port -h $host -c "COPY test_table TO STDOUT
WITH BINARY;" > /dev/null
end_time=$(perl -MTime::HiRes=time -e 'printf "%.9f\n", time')
elapsed_time=$(perl -e "printf('%.9f', ($end_time -
$start_time) + $elapsed_time)")
done
avg_elapsed_time_in_ms=$(perl -e "printf('%.9f', ($elapsed_time / 30))")
echo $avg_elapsed_time_in_ms
done
