Re: [HACKERS] max_worker_processes on the standby

On Sat, Dec 5, 2015 at 12:56 AM, Alvaro Herrera
<alvherre(at)2ndquadrant(dot)com> wrote:
> Fujii Masao wrote:
>
>> Sorry for not reviewing the patch before you push it...
>>
>> In HEAD, I ran very simple test case:
>>
>> 1. enable track_commit_timestamp
>> 2. start the server
>> 3. run some transactions
>> 4. execute pg_last_committed_xact() -- returns non-null values
>> 5. shutdown the server with immdiate mode
>> 6. restart the server -- crash recovery happens
>> 7. execute pg_last_committed_xact()
>>
>> The last call of pg_last_committed_xact() returns NULL values, which means
>> that the xid and timestamp information of the last committed transaction
>> disappeared by crash recovery. Isn't this a bug?
>
> Hm, not really, because the status of the "last" transaction is kept in
> shared memory as a cache and not expected to live across a restart.
> However, I tested the equivalent scenario:
>
> alvherre=# create table fg();
> CREATE TABLE
>
> alvherre=# select ts.* from pg_class,pg_xact_commit_timestamp(xmin) ts where relname = 'fg';
> ts
> -------------------------------
> 2015-12-04 12:41:48.017976-03
> (1 fila)
>
> then crash the server, and after recovery the data is gone:
>
> alvherre=# select ts.*, xmin, c.relname from pg_class c,pg_xact_commit_timestamp(xmin) ts where relname = 'fg';
> ts | xmin | relname
> ----+------+---------
> | 630 | fg
> (1 fila)
>
> Not sure what is going on; my reading of the code certainly says that
> the data should be there. I'm looking into it.
>
> I also noticed that I didn't actually push the whole of the patch
> yesterday -- I neglected to "git add" the latest changes, the ones that
> fix the promotion scenario :-( so the commit messages is misleading
> because it describes something that's not there.

So firstly you will push those "latest" changes soon?

Regards,

--
Fujii Masao