Hello Dilip,
While testing the v7 patches, I am observing a crash with the below test case.
Test case:
create tablespace tab location '<dir_path>/test_dir';
create tablespace tab1 location '<dir_path>/test_dir1';
create database test tablespace tab;
\c test
create table t( a int PRIMARY KEY,b text);
CREATE OR REPLACE FUNCTION large_val() RETURNS TEXT LANGUAGE SQL AS 'select array_agg(md5(g::text))::text from generate_series(1, 256) g';
insert into t values (generate_series(1,2000000), large_val());
alter table t set tablespace tab1 ;
\c postgres
create database test1 template test;
alter database test set tablespace pg_default;
alter database test set tablespace tab;
\c test1
alter table t set tablespace tab;
Logfile says:
2021-12-08 23:31:58.855 +04 [134252] PANIC: could not fsync file "base/16386/4152": No such file or directory
2021-12-08 23:31:59.398 +04 [134251] LOG: checkpointer process (PID 134252) was terminated by signal 6: Aborted
Thanks.
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Regards,
Neha Sharma
On Mon, Dec 6, 2021 at 7:53 PM Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
>
> Thank you, Dilip for the quick response. I am okay with the changes done in the v7 patch.
>
> One last point - If we try to clone a huge database, as expected CREATE DATABASE emits a lot of WALs, causing a lot of intermediate checkpoints which seems to be affecting the performance slightly.
Yeah, that is a valid point because instead of just one WAL for
createdb we will generate WAL for each page in the database, so I
agree that if the max_wal_size is not enough for those WALs then we
might have to pay the cost of multiple checkpoints. However, if we
compare it with the current mechanism then now it is a forced
checkpoint and there is no way to avoid it whereas with the new
approach user can set enough max_wal_size and they can avoid it. So
in other words now the checkpoint is driven by the amount of resource
which is true for any other operation e.g. ALTER TABLE SET TABLESPACE
so now it is in more sync with the rest of the system, but without the
patch, it was a special purpose forced checkpoint only for the
createdb.
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Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com