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Date: Mon, 7 Dec 2015 22:33:43 +0900
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Subject: Re: [HACKERS] max_worker_processes on the standby
From: Fujii Masao <masao.fujii@gmail.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Petr Jelinek <petr@2ndquadrant.com>,
 oonishitk@nttdata.co.jp, pgsql-docs <pgsql-docs@postgresql.org>,
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On Sat, Dec 5, 2015 at 12:56 AM, Alvaro Herrera
<alvherre@2ndquadrant.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


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