Re: standby recovery fails (tablespace related) (tentative patch anddiscussion)

Thanks. I updated the patch to v5. It passes install-check testing and recovery testing.

Hi,
Thank you for working on this fix.
The overall design of the latest version looks good to me.
But during the review, I found a bug in the current implementation.
New behavior must apply to crash-recovery only, now it applies to archiveRecovery too.
That can cause a silent loss of a tablespace during regular standby operation
since it never calls CheckRecoveryConsistency().

Steps to reproduce:
1) run master and replica
2) create dir for tablespace:
mkdir  /tmp/tblspc1

3) create tablespace and database on the master:
create tablespace tblspc1 location '/tmp/tblspc1';
create database db1 tablespace tblspc1 ;

4) wait for replica to receive this changes and pause replication:
select pg_wal_replay_pause();

5) move replica's tablespace symlink to some empty directory, i.e. /tmp/tblspc2
mkdir  /tmp/tblspc2
ln -sfn /tmp/tblspc2 postgresql_data_replica/pg_tblspc/16384

6) create another database in tblspc1 on master:
create database db2 tablespace tblspc1 ;

7) resume replication on standby:
select pg_wal_replay_resume();

8) try to connect to db2 on standby

It's expected that dbase_redo() will fail because the directory on standby is not found.
While with the patch it suppresses the error until we attempt to connect db2 on the standby:

2019-08-22 18:34:39.178 MSK [21066] HINT:  Execute pg_wal_replay_resume() to continue.
2019-08-22 18:42:41.656 MSK [21066] WARNING:  Skip creating database directory "pg_tblspc/16384/PG_13_201908012". The dest tablespace may have been removed before abnormal shutdown. If the removal is illegal after later checking we will panic.
2019-08-22 18:42:41.656 MSK [21066] CONTEXT:  WAL redo at 0/3027738 for Database/CREATE: copy dir base/1 to pg_tblspc/16384/PG_13_201908012/16390
2019-08-22 18:42:46.096 MSK [21688] FATAL:  "pg_tblspc/16384/PG_13_201908012/16390" is not a valid data directory
2019-08-22 18:42:46.096 MSK [21688] DETAIL:  File "pg_tblspc/16384/PG_13_201908012/16390/PG_VERSION" is missing.

Also some nitpicking about code style:
1) Please, add comment to forget_missing_directory().

2) +               elog(LOG, "Directory \"%s\" was missing during directory copying "
I think we'd better update this message elevel to WARNING.

3) Shouldn't we also move FlushDatabaseBuffers(xlrec->src_db_id); call under
    if (do_copydir) clause?
I don't see a reason to flush pages that we won't use later.

-- 
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company