On 7/13/23 02:41, Boris Sagadin wrote:
Hi,
restoring a 1.5TB database with about 800k tables on i3.4xlarge AWS
instace, PgSQL V12.15 on Ubuntu.
Running pg_restore with -j 16, I noticed the pg_restore is busy for an
hour or so with IO at 80%+ and then most of processes start idling and
only a few doing some work, disk IO at 1-2%, pg_stat_activity is mostly
idle, same goes for CPU, and this state proceeds for further 6 hours, disk
space increases very slowly.
I thought because of a lot of small tables, number of workers should be
increased to increase parallel efficiency, so I tried with -j 128. The
situation was somewhat better, but most of the workers start idling, again
disk IO lowers to about 4% util, CPU util goes to about 4%, too.
Stracing workers produces the perpetual read call on most pg_restore workers:
# strace -p 59567
strace: Process 59567 attached
read(3,
With only about 10 or so (out of 128) workers doing some actual work:
strace -p 59367 -e sendto
strace: Process 59367 attached
sendto(4, "Q\0\0\0\263ALTER TABLE ONLY raw.space0"..., 180, MSG_NOSIGNAL,
NULL, 0) = 180
sendto(4, "Q\0\0\0.TRUNCATE TABLE ONLY raw.spa"..., 47, MSG_NOSIGNAL,
NULL, 0) = 47
sendto(4, "Q\0\0\0\205COPY raw.space000448117 (da"..., 134, MSG_NOSIGNAL,
NULL, 0) = sendto(4, "Q\0\0\0\vCOMMIT\0", 12, MSG_NOSIGNAL, NULL, 0) = 12
sendto(4, "Q\0\0\0pCREATE INDEX idx_space00044"..., 113, MSG_NOSIGNAL,
NULL, 0) = 113
sendto(4, "Q\0\0\0\263ALTER TABLE ONLY raw.space0"..., 180, MSG_NOSIGNAL,
NULL, 0) = 180
...
.. some lines omitted
I would think that all workers would proceed with creating indexes and
doing some useful work until the restore is finished completely?
Most of the tables are very small, 2 indexes per table and without any
foreign references etc., we have a multi tenant environment.
I always run pg_dump and pg_restore with "--verbose", and redirect stdout &
stderr to a log file. Then I "tail -f" that log file. It'll tell you what's
happening.
Also, iotop is quite useful.
--
Born in Arizona, moved to Babylonia.
