Re: [HACKERS] Logical Replication WIP

On 17/12/16 18:34, Steve Singer wrote:
> On 12/16/2016 07:49 AM, Petr Jelinek wrote:
>> Hi,
>>
>> attached is version 13 of the patch.
>>
>> I merged in changes from PeterE. And did following changes:
>> - fixed the ownership error messages for both provider and subscriber
>> - added ability to send invalidation message to invalidate whole
>> relcache and use it in publication code
>> - added the post creation/alter/drop hooks
>> - removed parts of docs that refer to initial sync (which does not exist
>> yet)
>> - added timeout handling/retry, etc to apply/launcher based on the GUCs
>> that exist for wal receiver (they could use renaming though)
>> - improved feedback behavior
>> - apply worker now uses owner of the subscription as connection user
>> - more tests
>> - check for max_replication_slots in launcher
>> - clarify the update 'K' sub-message description in protocol
> 
> A few things I've noticed so far
> 
> If I shutdown the publisher I see the following in the log
> 
> 2016-12-17 11:33:49.548 EST [1891] LOG:  worker process: ?)G? (PID 1987)
> exited with exit code 1
> 
> but then if I shutdown the subscriber postmaster and restart it switches to
> 2016-12-17 11:43:09.628 EST [2373] LOG:  worker process: ???? (PID 2393)
> exited with exit code 1
> 
> Not sure where the 'G' was coming from (other times I have seen an 'I'
> here or other random characters)
> 

Uninitialized bgw_name for apply worker. Rather silly bug. Fixed.

> 
> I don't think we are cleaning up subscriptions on a drop database
> 
> If I do the following
> 
> 1) Create a subscription in a new database
> 2) Stop the publisher
> 3) Drop the database on the subscriber
> 
> test=# create subscription mysuba connection 'host=localhost dbname=test
> port=5440' publication mypub;
> test=# \c b
> b=# drop database test;
> DROP DATABASE
> b=# select * FROM pg_subscription ;
>  subdbid | subname | subowner | subenabled | subconninfo              |
> subslotname | subpublications
> ---------+---------+----------+------------+--------------------------------------+-------------+-----------------
> 
>    16384 | mysuba  |       10 | t          | host=localhost dbname=test
> port=5440 | mysuba      | {mypub}
> 

Good one. I added check that prevents dropping database when there is
subscription defined for it. I think we can't cascade here as
subscription may or may not hold resources (slot) in another
instance/database so preventing the drop is best we can do.

> 
> Also I don't think I can now drop mysuba
> b=# drop subscription mysuba;
> ERROR:  subscription "mysuba" does not exist
> 

Yeah subscriptions are per database.

I don't want to make v14 just for these 2 changes as that would make
life harder for anybody code-reviewing the v13 so attached is diff with
above fixes that applies on top of v13.

-- 
  Petr Jelinek                  http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services

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