Hi all:
I am trying to understand when the bgwriter is written.
I thought that the bgwriter.c's calling turn is:
BackgroundWriterMain ->BgBufferSync-> SyncOneBuffer
And In my postgresql.conf , the bgwriter_delay=200ms.
I did the following:
postgres=# select * from testtab;
id | val
----+-------
1 | 12345
(1 row)
postgres=# update testtab set val='54321' where id=1;
UPDATE 1
postgres=# select * from testtab;
id | val
----+-------
1 | 54321
(1 row)
postgres=#
Now I can say the buffer is dirty ,right?
I wait for a few minutes, I can found bgwriter's BackgroundWriterMain called BgBufferSync many times.
But I can't find BgBufferSync really call SyncOneBuffer to put the dirty data todisk.
Untill I close the postgres process, I can find the SyncOneBuffer is called for many times.
My question is:
Why even there are dirty buffer(s), the SyncOneBuffer is still not called?
Is it violating the background writer's purpose?
Or the flushing to disk will be done untill the amount of block/buffer is satisfied? If so , what is it?
Thanks in advance for any help