Re: crash-recovery replay of CREATE TABLESPACE is broken in HEAD

On 18/07/10 08:22, Bruce Momjian wrote:
> The bug is that we can't replay mkdir()/symlink() and assume those will
> always succeed. I looked at the createdb redo code and it basically
> drops the directory before creating it.
>
> The tablespace directory/symlink setup is more complex, so I just wrote
> the attached patch to trigger a redo-'delete' tablespace operation
> before the create tablespace redo operation.

Redoing a drop talespace assumes the tablespace directory is empty,
which it necessarily isn't when redoing a create tablespace command:

postgres=# CREATE TABLESPACE t LOCATION '/tmp/t';
CREATE TABLESPACE
postgres=# CREATE TABLE tfoo (id int4) TABLESPACE t;
CREATE TABLE
postgres=# \q
$ killall -9 postmaster
$ bin/postmaster -D data
LOG: database system was interrupted; last known up at 2010-07-18
08:48:32 EEST
LOG: database system was not properly shut down; automatic recovery in
progress
LOG: consistent recovery state reached at 0/5E889C
LOG: redo starts at 0/5E889C
FATAL: tablespace 16402 is not empty
CONTEXT: xlog redo create ts: 16402 "/tmp/t"
LOG: startup process (PID 5987) exited with exit code 1
LOG: aborting startup due to startup process failure

Also, casting the xl_tblspc_create_rec as xl_tblspc_drop_rec is a bit
questionable. It works because both structs begin with the tablespace
Oid, but it doesn't look right, and can break in hard-to-notice ways in
the future if the structure of those structs change in the future.

> Ignoring mkdir/symlink creation failure is not an option because the
> symlink might point to some wrong location or something.

Maybe you should check that it points to the right location? Or drop and
recreate the symlink, and ignore failure at mkdir.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com