| From: | Simon Riggs <simon(dot)riggs(at)2ndquadrant(dot)com> |
|---|---|
| To: | Craig Ringer <craig(at)2ndquadrant(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Thom Brown <thom(at)linux(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Logical decoding on standby |
| Date: | 2017-03-29 15:13:35 |
| Message-ID: | CANP8+jLNj_xKgnRJXiHKVOG3f7THkkdJK3a==Fdk1A98aGTbgQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 29 March 2017 at 10:17, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
> On 29 March 2017 at 16:44, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
>
>> * Split oldestCatalogXmin tracking into separate patch
>
> Regarding this, Simon raised concerns about xlog volume here.
>
> It's pretty negligible.
>
> We only write a new record when a vacuum runs after catalog_xmin
> advances on the slot with the currently-lowest catalog_xmin (or, if
> vacuum doesn't run reasonably soon, when the bgworker next looks).
I'd prefer to slow things down a little, not be so eager.
If we hold back update of the catalog_xmin until when we run
GetRunningTransactionData() we wouldn't need to produce any WAL
records at all AND we wouldn't need to have VACUUM do
UpdateOldestCatalogXmin(). Bgwriter wouldn't need to perform an extra
task.
That would also make this patch about half the length it is.
Let me know what you think.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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