pg_restore scan
I'm trying to troubleshoot the slowness issue with pg_restore and stumbled
across a recent post about pg_restore scanning the whole file :
"scanning happens in a very inefficient way, with many seek calls and
small block reads. Try strace to see them. This initial phase can take
hours in a huge dump file, before even starting any actual restoration."
see :
/messages/by-id/E48B611D-7D61-4575-A820-B2C3EC2E0551@gmx.net
I'm currently having this same issue.
At the early stage of restoration I can see lots of disk writes activities
but as time goes by, disk writes activities are reduced.
I can see the COPY process in postgres but not using any CPU, and the
process that uses CPU are pg_restores.
I can recreate this issue when restoring a specific table to stdout.
ie :
pg_restore -vvvv -t <some_table_at_the> DB.pgdump -f -
If the table is at the bottom of the TOC it will take hours before I get a
result, but I get an almost immediate result when the table is at the top.
parallel restore suffers with the same issue where each process has to
perform a scan for each table.
What is the best way to speed up the restore ?
More info about my environment :
pg_restore (PostgreSQL) 17.6
Archive :
; Archive created at 2025-09-16 16:08:28 AEST
; dbname: DB
; TOC Entries: 8221
; Compression: none
; Dump Version: 1.14-0
; Format: CUSTOM
; Integer: 4 bytes
; Offset: 8 bytes
; Dumped from database version: 14.15
; Dumped by pg_dump version: 14.19 (Ubuntu 14.19-1.pgdg22.04+1)
On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue with pg_restore and
stumbled across a recent post about pg_restore scanning the whole file :"scanning happens in a very inefficient way, with many seek calls and
small block reads. Try strace to see them. This initial phase can take
hours in a huge dump file, before even starting any actual restoration."
see : /messages/by-id/E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <https://www.postgresql.org/message-id/
E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net>
This was for pg_dump output that was streamed to a Borg archive and as
result had no object offsets in the TOC.
How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>
On Wed, 17 Sept 2025 at 08:36, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:
Show quoted text
On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue with pg_restore and
stumbled across a recent post about pg_restore scanning the whole file :"scanning happens in a very inefficient way, with many seek calls and
small block reads. Try strace to see them. This initial phase can take
hours in a huge dump file, before even starting any actual restoration."
see : /messages/by-id/E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <https://www.postgresql.org/message-id/
E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net>This was for pg_dump output that was streamed to a Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com
So, piping or redirecting to a file? If so, then that's the problem.
pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump 2> ${db}.log
On Tue, Sep 16, 2025 at 8:54 PM R Wahyudi <rwahyudi@gmail.com> wrote:
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue with pg_restore and
stumbled across a recent post about pg_restore scanning the whole file :"scanning happens in a very inefficient way, with many seek calls
and
small block reads. Try strace to see them. This initial phase can take
hours in a huge dump file, before even starting any actual restoration."
see : /messages/by-id/E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <https://www.postgresql.org/message-id/
E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net>This was for pg_dump output that was streamed to a Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
On 9/16/25 17:54, R Wahyudi wrote:
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>
What do you do with the output?
--
Adrian Klaver
adrian.klaver@aklaver.com
Sorry for not including the full command - yes , its piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best > <filenamegoeshere>
I think we found the issue! I'll do further testing and see how it goes !
On Wed, 17 Sept 2025 at 11:02, Ron Johnson <ronljohnsonjr@gmail.com> wrote:
Show quoted text
So, piping or redirecting to a file? If so, then that's the problem.
pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump 2> ${db}.logOn Tue, Sep 16, 2025 at 8:54 PM R Wahyudi <rwahyudi@gmail.com> wrote:
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue with pg_restore and
stumbled across a recent post about pg_restore scanning the whole file:
"scanning happens in a very inefficient way, with many seek calls
and
small block reads. Try strace to see them. This initial phase can take
hours in a huge dump file, before even starting any actualrestoration."
see : /messages/by-id/E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <https://www.postgresql.org/message-id/
E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net>This was for pg_dump output that was streamed to a Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
PG 17 has integrated zstd compression, while --format=directory lets you do
multi-threaded dumps. That's much faster than a single-threaded pg_dump
into a multi-threaded compression program.
(If for _Reasons_ you require a single-file backup, then tar the directory
of compressed files using the --remove-files option.)
On Tue, Sep 16, 2025 at 10:50 PM R Wahyudi <rwahyudi@gmail.com> wrote:
Sorry for not including the full command - yes , its piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best > <filenamegoeshere>I think we found the issue! I'll do further testing and see how it goes !
On Wed, 17 Sept 2025 at 11:02, Ron Johnson <ronljohnsonjr@gmail.com>
wrote:So, piping or redirecting to a file? If so, then that's the problem.
pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump 2> ${db}.logOn Tue, Sep 16, 2025 at 8:54 PM R Wahyudi <rwahyudi@gmail.com> wrote:
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue with pg_restore and
stumbled across a recent post about pg_restore scanning the wholefile :
"scanning happens in a very inefficient way, with many seek calls
and
small block reads. Try strace to see them. This initial phase can
take
hours in a huge dump file, before even starting any actual
restoration."
see : /messages/by-id/E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <https://www.postgresql.org/message-id/
E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net>This was for pg_dump output that was streamed to a Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
Hi All,
Thanks for the quick and accurate response! I never been so happy seeing
IOwait on my system!
I might be blind as I can't find information about 'offset' in pg_dump
documentation.
Where can I find more info about this?
Regards,
Rianto
On Wed, 17 Sept 2025 at 13:48, Ron Johnson <ronljohnsonjr@gmail.com> wrote:
Show quoted text
PG 17 has integrated zstd compression, while --format=directory lets you
do multi-threaded dumps. That's much faster than a single-threaded pg_dump
into a multi-threaded compression program.(If for _Reasons_ you require a single-file backup, then tar the directory
of compressed files using the --remove-files option.)On Tue, Sep 16, 2025 at 10:50 PM R Wahyudi <rwahyudi@gmail.com> wrote:
Sorry for not including the full command - yes , its piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best > <filenamegoeshere>I think we found the issue! I'll do further testing and see how it goes !
On Wed, 17 Sept 2025 at 11:02, Ron Johnson <ronljohnsonjr@gmail.com>
wrote:So, piping or redirecting to a file? If so, then that's the problem.
pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump 2> ${db}.logOn Tue, Sep 16, 2025 at 8:54 PM R Wahyudi <rwahyudi@gmail.com> wrote:
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue with pg_restore and
stumbled across a recent post about pg_restore scanning the wholefile :
"scanning happens in a very inefficient way, with many seek calls
and
small block reads. Try strace to see them. This initial phase can
take
hours in a huge dump file, before even starting any actual
restoration."
see : /messages/by-id/E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <https://www.postgresql.org/message-id/
E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net>This was for pg_dump output that was streamed to a Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
It's towards the end of this long mailing list thread from a couple of
weeks ago.
https://www.postgrespro.com/list/id/s0491qrn-343s-0757-8sn5-120rr8610qqq@tzk.arg
On Thu, Sep 18, 2025 at 8:58 AM R Wahyudi <rwahyudi@gmail.com> wrote:
Hi All,
Thanks for the quick and accurate response! I never been so happy seeing
IOwait on my system!I might be blind as I can't find information about 'offset' in pg_dump
documentation.
Where can I find more info about this?Regards,
RiantoOn Wed, 17 Sept 2025 at 13:48, Ron Johnson <ronljohnsonjr@gmail.com>
wrote:PG 17 has integrated zstd compression, while --format=directory lets you
do multi-threaded dumps. That's much faster than a single-threaded pg_dump
into a multi-threaded compression program.(If for _Reasons_ you require a single-file backup, then tar the
directory of compressed files using the --remove-files option.)On Tue, Sep 16, 2025 at 10:50 PM R Wahyudi <rwahyudi@gmail.com> wrote:
Sorry for not including the full command - yes , its piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best > <filenamegoeshere>I think we found the issue! I'll do further testing and see how it goes !
On Wed, 17 Sept 2025 at 11:02, Ron Johnson <ronljohnsonjr@gmail.com>
wrote:So, piping or redirecting to a file? If so, then that's the problem.
pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump 2> ${db}.logOn Tue, Sep 16, 2025 at 8:54 PM R Wahyudi <rwahyudi@gmail.com> wrote:
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver <
adrian.klaver@aklaver.com> wrote:On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue with pg_restore and
stumbled across a recent post about pg_restore scanning the wholefile :
"scanning happens in a very inefficient way, with many seek
calls and
small block reads. Try strace to see them. This initial phase can
take
hours in a huge dump file, before even starting any actual
restoration."
see :
/messages/by-id/E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <https://www.postgresql.org/message-id/
E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net>This was for pg_dump output that was streamed to a Borg archive and
as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
On 9/18/25 05:58, R Wahyudi wrote:
Hi All,
Thanks for the quick and accurate response! I never been so happy
seeing IOwait on my system!
Because?
What did you find?
I might be blind as I can't find information about 'offset' in pg_dump
documentation.
Where can I find more info about this?
It is not in the user documentation.
From the thread Ron referred to, there is an explanation here:
/messages/by-id/366773.1756749256@sss.pgh.pa.us
I believe the actual code, for the -Fc format, is in pg_backup_custom.c
here:
https://github.com/postgres/postgres/blob/master/src/bin/pg_dump/pg_backup_custom.c#L723
Per comment at line 755:
"
If possible, re-write the TOC in order to update the data offset
information. This is not essential, as pg_restore can cope in most
cases without it; but it can make pg_restore significantly faster
in some situations (especially parallel restore). We can skip this
step if we're not dumping any data; there are no offsets to update
in that case.
"
Regards,
RiantoOn Wed, 17 Sept 2025 at 13:48, Ron Johnson <ronljohnsonjr@gmail.com
<mailto:ronljohnsonjr@gmail.com>> wrote:PG 17 has integrated zstd compression, while --format=directory lets
you do multi-threaded dumps. That's much faster than a single-
threaded pg_dump into a multi-threaded compression program.(If for _Reasons_ you require a single-file backup, then tar the
directory of compressed files using the --remove-files option.)On Tue, Sep 16, 2025 at 10:50 PM R Wahyudi <rwahyudi@gmail.com
<mailto:rwahyudi@gmail.com>> wrote:Sorry for not including the full command - yes , its piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best > <filenamegoeshere>I think we found the issue! I'll do further testing and see how
it goes !On Wed, 17 Sept 2025 at 11:02, Ron Johnson
<ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com>> wrote:So, piping or redirecting to a file? If so, then that's the
problem.pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump
2> ${db}.logOn Tue, Sep 16, 2025 at 8:54 PM R Wahyudi
<rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>> wrote:pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver
<adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>> wrote:On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue
with pg_restore and
stumbled across a recent post about pg_restore
scanning the whole file :
> "scanning happens in a very inefficient way,
with many seek calls and
small block reads. Try strace to see them. This
initial phase can take
hours in a huge dump file, before even starting
any actual restoration."
E48B611D-7D61-4575-A820- <https://
www.postgresql.org/message-id/E48B611D-7D61-4575-A820->B2C3EC2E0551%40gmx.net <http://40gmx.net>
<https://www.postgresql.org/message-id/ <https://
www.postgresql.org/message-id/>E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net
This was for pg_dump output that was streamed to a
Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
--
Adrian Klaver
adrian.klaver@aklaver.com
I've been given a database dump file daily and I've been asked to restore
it.
I tried everything I could to speed up the process, including using -j 40.
I discovered that at the later stage of the restore process, the
following behaviour repeated a few times :
40 x pg_restore process doing 100% CPU
40 x postgres process doing COPY but using 0% CPU
..... and zero disk write activity
I don't see this behaviour when restoring the database that was dumped with
-Fd.
Also with an un-piped backup file, I can restore a specific table without
having to wait for hours.
--
On Fri, 19 Sept 2025 at 01:54, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:
Show quoted text
On 9/18/25 05:58, R Wahyudi wrote:
Hi All,
Thanks for the quick and accurate response! I never been so happy
seeing IOwait on my system!Because?
What did you find?
I might be blind as I can't find information about 'offset' in pg_dump
documentation.
Where can I find more info about this?It is not in the user documentation.
From the thread Ron referred to, there is an explanation here:
/messages/by-id/366773.1756749256@sss.pgh.pa.us
I believe the actual code, for the -Fc format, is in pg_backup_custom.c
here:https://github.com/postgres/postgres/blob/master/src/bin/pg_dump/pg_backup_custom.c#L723
Per comment at line 755:
"
If possible, re-write the TOC in order to update the data offset
information. This is not essential, as pg_restore can cope in most
cases without it; but it can make pg_restore significantly faster
in some situations (especially parallel restore). We can skip this
step if we're not dumping any data; there are no offsets to update
in that case.
"Regards,
RiantoOn Wed, 17 Sept 2025 at 13:48, Ron Johnson <ronljohnsonjr@gmail.com
<mailto:ronljohnsonjr@gmail.com>> wrote:PG 17 has integrated zstd compression, while --format=directory lets
you do multi-threaded dumps. That's much faster than a single-
threaded pg_dump into a multi-threaded compression program.(If for _Reasons_ you require a single-file backup, then tar the
directory of compressed files using the --remove-files option.)On Tue, Sep 16, 2025 at 10:50 PM R Wahyudi <rwahyudi@gmail.com
<mailto:rwahyudi@gmail.com>> wrote:Sorry for not including the full command - yes , its piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best > <filenamegoeshere>I think we found the issue! I'll do further testing and see how
it goes !On Wed, 17 Sept 2025 at 11:02, Ron Johnson
<ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com>>wrote:
So, piping or redirecting to a file? If so, then that's the
problem.pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump
2> ${db}.logOn Tue, Sep 16, 2025 at 8:54 PM R Wahyudi
<rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>> wrote:pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver
<adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>> wrote:On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue
with pg_restore and
stumbled across a recent post about pg_restore
scanning the whole file :
"scanning happens in a very inefficient way,
with many seek calls and
small block reads. Try strace to see them. This
initial phase can take
hours in a huge dump file, before even starting
any actual restoration."
E48B611D-7D61-4575-A820- <https://
www.postgresql.org/message-id/E48B611D-7D61-4575-A820->
B2C3EC2E0551%40gmx.net <http://40gmx.net>
<https://www.postgresql.org/message-id/ <https://
www.postgresql.org/message-id/>E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net
This was for pg_dump output that was streamed to a
Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Adrian Klaver
adrian.klaver@aklaver.com
On 9/18/25 2:36 PM, R Wahyudi wrote:
I've been given a database dump file daily and I've been asked to
restore it.
I tried everything I could to speed up the process, including using -j 40.I discovered that at the later stage of the restore process, the
following behaviour repeated a few times :
40 x pg_restore process doing 100% CPU
40 x postgres process doing COPY but using 0% CPU
..... and zero disk write activityI don't see this behaviour when restoring the database that was dumped
with -Fd.
Also with an un-piped backup file, I can restore a specific table
without having to wait for hours.
From the docs:
https://www.postgresql.org/docs/current/app-pgrestore.html
"
-j number-of-jobs
Only the custom and directory archive formats are supported with this
option. The input must be a regular file or directory (not, for example,
a pipe or standard input). Also, multiple jobs cannot be used together
with the option --single-transaction.
"
--
On Fri, 19 Sept 2025 at 01:54, Adrian Klaver <adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>> wrote:On 9/18/25 05:58, R Wahyudi wrote:
Hi All,
Thanks for the quick and accurate response! I never been so happy
seeing IOwait on my system!Because?
What did you find?
I might be blind as I can't find information about 'offset' in
pg_dump
documentation.
Where can I find more info about this?It is not in the user documentation.
From the thread Ron referred to, there is an explanation here:
https://www.postgresql.org/message-
id/366773.1756749256%40sss.pgh.pa.us <https://www.postgresql.org/
message-id/366773.1756749256%40sss.pgh.pa.us>I believe the actual code, for the -Fc format, is in pg_backup_custom.c
here:https://github.com/postgres/postgres/blob/master/src/bin/pg_dump/
pg_backup_custom.c#L723 <https://github.com/postgres/postgres/blob/
master/src/bin/pg_dump/pg_backup_custom.c#L723>Per comment at line 755:
"
If possible, re-write the TOC in order to update the data offset
information. This is not essential, as pg_restore can cope in most
cases without it; but it can make pg_restore significantly faster
in some situations (especially parallel restore). We can skip this
step if we're not dumping any data; there are no offsets to update
in that case.
"Regards,
RiantoOn Wed, 17 Sept 2025 at 13:48, Ron Johnson
<ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com>
<mailto:ronljohnsonjr@gmail.com
<mailto:ronljohnsonjr@gmail.com>>> wrote:
PG 17 has integrated zstd compression, while --
format=directory lets
you do multi-threaded dumps. That's much faster than a single-
threaded pg_dump into a multi-threaded compression program.(If for _Reasons_ you require a single-file backup, then tar the
directory of compressed files using the --remove-files option.)On Tue, Sep 16, 2025 at 10:50 PM R Wahyudi
<rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>
<mailto:rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>>> wrote:
Sorry for not including the full command - yes , its
piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best ><filenamegoeshere>
I think we found the issue! I'll do further testing and
see how
it goes !
On Wed, 17 Sept 2025 at 11:02, Ron Johnson
<ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com><mailto:ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com>>>
wrote:So, piping or redirecting to a file? If so, then
that's the
problem.
pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump
2> ${db}.logOn Tue, Sep 16, 2025 at 8:54 PM R Wahyudi
<rwahyudi@gmail.com <mailto:rwahyudi@gmail.com><mailto:rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>>> wrote:
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver
<adrian.klaver@aklaver.com<mailto:adrian.klaver@aklaver.com>
<mailto:adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>>> wrote:
On 9/16/25 15:25, R Wahyudi wrote:
>
> I'm trying to troubleshoot the slowness issue
with pg_restore and
> stumbled across a recent post about pg_restore
scanning the whole file :
>
> > "scanning happens in a very inefficientway,
with many seek calls and
> small block reads. Try strace to see them.This
initial phase can take
> hours in a huge dump file, before evenstarting
any actual restoration."
> see : https://www.postgresql.org/message-id/ </messages/by-id/>
E48B611D-7D61-4575-A820- <https://
www.postgresql.org/message-id/E48B611D-7D61-4575-A820- <http://www.postgresql.org/message-id/E48B611D-7D61-4575-A820->>
> B2C3EC2E0551%40gmx.net <http://40gmx.net>
<http://40gmx.net <http://40gmx.net>>
</messages/by-id/> <https://
www.postgresql.org/message-id/ <http://www.postgresql.org/
message-id/>>
> E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <http://40gmx.net>
<http://40gmx.net <http://40gmx.net>>>
This was for pg_dump output that was streamed
to a
Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
<mailto:adrian.klaver@aklaver.com<mailto:adrian.klaver@aklaver.com>>
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
--
Adrian Klaver
adrian.klaver@aklaver.com
The input must be a regular file or directory (not, for example, a pipe
or standard input).
Thanks again for the pointer!
I successfully ran a parallel restore with no warnings presented.
I didn't really pay attention to how the dump was taken until I
accidentally stumbled upon your post.
Regards,
Rianto
On Fri, 19 Sept 2025 at 07:45, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:
Show quoted text
On 9/18/25 2:36 PM, R Wahyudi wrote:
I've been given a database dump file daily and I've been asked to
restore it.
I tried everything I could to speed up the process, including using -j40.
I discovered that at the later stage of the restore process, the
following behaviour repeated a few times :
40 x pg_restore process doing 100% CPU
40 x postgres process doing COPY but using 0% CPU
..... and zero disk write activityI don't see this behaviour when restoring the database that was dumped
with -Fd.
Also with an un-piped backup file, I can restore a specific table
without having to wait for hours.From the docs:
https://www.postgresql.org/docs/current/app-pgrestore.html
"
-j number-of-jobsOnly the custom and directory archive formats are supported with this
option. The input must be a regular file or directory (not, for example,
a pipe or standard input). Also, multiple jobs cannot be used together
with the option --single-transaction.
"--
On Fri, 19 Sept 2025 at 01:54, Adrian Klaver <adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>> wrote:On 9/18/25 05:58, R Wahyudi wrote:
Hi All,
Thanks for the quick and accurate response! I never been so happy
seeing IOwait on my system!Because?
What did you find?
I might be blind as I can't find information about 'offset' in
pg_dump
documentation.
Where can I find more info about this?It is not in the user documentation.
From the thread Ron referred to, there is an explanation here:
https://www.postgresql.org/message-
id/366773.1756749256%40sss.pgh.pa.us <https://www.postgresql.org/
message-id/366773.1756749256%40sss.pgh.pa.us>I believe the actual code, for the -Fc format, is in
pg_backup_custom.c
here:
https://github.com/postgres/postgres/blob/master/src/bin/pg_dump/
pg_backup_custom.c#L723 <https://github.com/postgres/postgres/blob/
master/src/bin/pg_dump/pg_backup_custom.c#L723>Per comment at line 755:
"
If possible, re-write the TOC in order to update the data offset
information. This is not essential, as pg_restore can cope in most
cases without it; but it can make pg_restore significantly faster
in some situations (especially parallel restore). We can skip this
step if we're not dumping any data; there are no offsets to update
in that case.
"Regards,
RiantoOn Wed, 17 Sept 2025 at 13:48, Ron Johnson
<ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com>
<mailto:ronljohnsonjr@gmail.com
<mailto:ronljohnsonjr@gmail.com>>> wrote:
PG 17 has integrated zstd compression, while --
format=directory lets
you do multi-threaded dumps. That's much faster than a
single-
threaded pg_dump into a multi-threaded compression program.
(If for _Reasons_ you require a single-file backup, then tar
the
directory of compressed files using the --remove-files
option.)
On Tue, Sep 16, 2025 at 10:50 PM R Wahyudi
<rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>
<mailto:rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>>>
wrote:
Sorry for not including the full command - yes , its
piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best ><filenamegoeshere>
I think we found the issue! I'll do further testing and
see how
it goes !
On Wed, 17 Sept 2025 at 11:02, Ron Johnson
<ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com><mailto:ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com>>>
wrote:So, piping or redirecting to a file? If so, then
that's the
problem.
pg_dump directly to a file puts file offsets in the
TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f${db}.dump
2> ${db}.log
On Tue, Sep 16, 2025 at 8:54 PM R Wahyudi
<rwahyudi@gmail.com <mailto:rwahyudi@gmail.com><mailto:rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>>> wrote:
pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d<database>
On Wed, 17 Sept 2025 at 08:36, Adrian Klaver
<adrian.klaver@aklaver.com<mailto:adrian.klaver@aklaver.com>
<mailto:adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>>> wrote:
On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness
issue
with pg_restore and
stumbled across a recent post about
pg_restore
scanning the whole file :
"scanning happens in a very inefficient
way,
with many seek calls and
small block reads. Try strace to see them.
This
initial phase can take
hours in a huge dump file, before even
starting
any actual restoration."
id/ </messages/by-id/>
E48B611D-7D61-4575-A820- <https://
www.postgresql.org/message-id/E48B611D-7D61-4575-A820- <http://www.postgresql.org/message-id/E48B611D-7D61-4575-A820->>
B2C3EC2E0551%40gmx.net <http://40gmx.net>
<http://40gmx.net <http://40gmx.net>>
</messages/by-id/> <https://
www.postgresql.org/message-id/ <http://www.postgresql.org/
message-id/>>
E48B611D-7D61-4575-A820-
B2C3EC2E0551%40gmx.net <http://40gmx.net>
<http://40gmx.net <http://40gmx.net>>>
This was for pg_dump output that was streamed
to a
Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>
<mailto:adrian.klaver@aklaver.com<mailto:adrian.klaver@aklaver.com>>
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>--
Adrian Klaver
adrian.klaver@aklaver.com
On Thu, Sep 18, 2025 at 5:37 PM R Wahyudi <rwahyudi@gmail.com> wrote:
I've been given a database dump file daily and I've been asked to restore
it.
I tried everything I could to speed up the process, including using -j 40.I discovered that at the later stage of the restore process, the
following behaviour repeated a few times :
40 x pg_restore process doing 100% CPU
Threads are not magic. IO and memory limitations still exist.
40 x postgres process doing COPY but using 0% CPU
..... and zero disk write activityI don't see this behaviour when restoring the database that was dumped
with -Fd.
Also with an un-piped backup file, I can restore a specific table without
having to wait for hours.
We explained this three days ago. Heck, it's in this very email. Click
on "the three dots", scroll down a bit.
On Fri, 19 Sept 2025 at 01:54, Adrian Klaver <adrian.klaver@aklaver.com>
wrote:On 9/18/25 05:58, R Wahyudi wrote:
Hi All,
Thanks for the quick and accurate response! I never been so happy
seeing IOwait on my system!Because?
What did you find?
I might be blind as I can't find information about 'offset' in pg_dump
documentation.
Where can I find more info about this?It is not in the user documentation.
From the thread Ron referred to, there is an explanation here:
/messages/by-id/366773.1756749256@sss.pgh.pa.us
I believe the actual code, for the -Fc format, is in pg_backup_custom.c
here:https://github.com/postgres/postgres/blob/master/src/bin/pg_dump/pg_backup_custom.c#L723
Per comment at line 755:
"
If possible, re-write the TOC in order to update the data offset
information. This is not essential, as pg_restore can cope in most
cases without it; but it can make pg_restore significantly faster
in some situations (especially parallel restore). We can skip this
step if we're not dumping any data; there are no offsets to update
in that case.
"Regards,
RiantoOn Wed, 17 Sept 2025 at 13:48, Ron Johnson <ronljohnsonjr@gmail.com
<mailto:ronljohnsonjr@gmail.com>> wrote:PG 17 has integrated zstd compression, while --format=directory lets
you do multi-threaded dumps. That's much faster than a single-
threaded pg_dump into a multi-threaded compression program.(If for _Reasons_ you require a single-file backup, then tar the
directory of compressed files using the --remove-files option.)On Tue, Sep 16, 2025 at 10:50 PM R Wahyudi <rwahyudi@gmail.com
<mailto:rwahyudi@gmail.com>> wrote:Sorry for not including the full command - yes , its piping to a
compression command :
| lbzip2 -n <threadsforbzipgoeshere>--best ><filenamegoeshere>
I think we found the issue! I'll do further testing and see how
it goes !On Wed, 17 Sept 2025 at 11:02, Ron Johnson
<ronljohnsonjr@gmail.com <mailto:ronljohnsonjr@gmail.com>>wrote:
So, piping or redirecting to a file? If so, then that's the
problem.pg_dump directly to a file puts file offsets in the TOC.
This how I do custom dumps:
cd $BackupDir
pg_dump -Fc --compress=zstd:long -v -d${db} -f ${db}.dump
2> ${db}.logOn Tue, Sep 16, 2025 at 8:54 PM R Wahyudi
<rwahyudi@gmail.com <mailto:rwahyudi@gmail.com>> wrote:pg_dump was done using the following command :
pg_dump -Fc -Z 0 -h <host> -U <user> -w -d <database>On Wed, 17 Sept 2025 at 08:36, Adrian Klaver
<adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>> wrote:On 9/16/25 15:25, R Wahyudi wrote:
I'm trying to troubleshoot the slowness issue
with pg_restore and
stumbled across a recent post about pg_restore
scanning the whole file :
"scanning happens in a very inefficient way,
with many seek calls and
small block reads. Try strace to see them. This
initial phase can take
hours in a huge dump file, before even starting
any actual restoration."
E48B611D-7D61-4575-A820- <https://
www.postgresql.org/message-id/E48B611D-7D61-4575-A820->
B2C3EC2E0551%40gmx.net <http://40gmx.net>
<https://www.postgresql.org/message-id/ <https://
www.postgresql.org/message-id/>E48B611D-7D61-4575-A820-B2C3EC2E0551%40gmx.net
This was for pg_dump output that was streamed to a
Borg archive and as
result had no object offsets in the TOC.How are you doing your pg_dump?
--
Adrian Klaver
adrian.klaver@aklaver.com
<mailto:adrian.klaver@aklaver.com>--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!--
Adrian Klaver
adrian.klaver@aklaver.com
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!