| Lists: | pgsql-hackers |
|---|
| From: | Sergey Konoplev <gray(dot)ru(at)gmail(dot)com> |
|---|---|
| To: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Cc: | Maxim Boguk <maxim(dot)boguk(at)gmail(dot)com> |
| Subject: | System catalog bloat removing safety |
| Date: | 2013-09-18 06:12:24 |
| Message-ID: | CAL_0b1v-QO6CB8quUgc-z1-3sGDB-Eig-ckJZm_qFHj+BSgsXQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hi all,
How safe is it to use the technique described by the link below with
system catalog tables to remove bloat?
(in a couple of words it is about moving tuples to the beginning of
the table with a special way of updating)
http://www.depesz.com/2010/10/17/reduce-bloat-of-table-without-longexclusive-locks/
Are there any caveats?
Thank you.
--
Kind regards,
Sergey Konoplev
PostgreSQL Consultant and DBA
http://www.linkedin.com/in/grayhemp
+1 (415) 867-9984, +7 (901) 903-0499, +7 (988) 888-1979
gray(dot)ru(at)gmail(dot)com
| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Sergey Konoplev <gray(dot)ru(at)gmail(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Maxim Boguk <maxim(dot)boguk(at)gmail(dot)com> |
| Subject: | Re: System catalog bloat removing safety |
| Date: | 2013-09-18 09:06:31 |
| Message-ID: | 20130918090631.GB13925@awork2.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2013-09-17 23:12:24 -0700, Sergey Konoplev wrote:
> How safe is it to use the technique described by the link below with
> system catalog tables to remove bloat?
>
> (in a couple of words it is about moving tuples to the beginning of
> the table with a special way of updating)
>
> http://www.depesz.com/2010/10/17/reduce-bloat-of-table-without-longexclusive-locks/
>
> Are there any caveats?
At least for pg_index it's not safe, we use the xmin of rows when
indcheckxmin = true.
I am not aware of other cases, but I'd be hesitant to do so.
You have bloat because of lots of temporary tables IIRC?
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
| From: | Sergey Konoplev <gray(dot)ru(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Maxim Boguk <maxim(dot)boguk(at)gmail(dot)com> |
| Subject: | Re: System catalog bloat removing safety |
| Date: | 2013-09-18 17:03:26 |
| Message-ID: | CAL_0b1tsce2KQmfhpk52v0qhAp_TRaTwm+Oi7SZY3Q0=LU2OnA@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Lists: | pgsql-hackers |
On Wed, Sep 18, 2013 at 2:06 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> On 2013-09-17 23:12:24 -0700, Sergey Konoplev wrote:
>> How safe is it to use the technique described by the link below with
>> system catalog tables to remove bloat?
>> (in a couple of words it is about moving tuples to the beginning of
>> the table with a special way of updating)
>> http://www.depesz.com/2010/10/17/reduce-bloat-of-table-without-longexclusive-locks/
>
> At least for pg_index it's not safe, we use the xmin of rows when
> indcheckxmin = true.
> I am not aware of other cases, but I'd be hesitant to do so.
Thank you, Andres, I did not know this. Just wondering, why it was
made of type bool and not xid?
> You have bloat because of lots of temporary tables IIRC?
Actually I am developing a bloat removing tool based on the updating technique:
https://code.google.com/p/pgtoolkit/source/browse/trunk/README
Now the --system-catalog feature marked as experimental. About
pg_index - I think the solution is to exclude it from processing
strictly.
Anyone has other ideas of what system tables it might be affected
except pg_index?
--
Kind regards,
Sergey Konoplev
PostgreSQL Consultant and DBA
http://www.linkedin.com/in/grayhemp
+1 (415) 867-9984, +7 (901) 903-0499, +7 (988) 888-1979
gray(dot)ru(at)gmail(dot)com