| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
| Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, "Ideriha, Takeshi" <ideriha(dot)takeshi(at)jp(dot)fujitsu(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com> |
| Subject: | Re: GUC for cleanup indexes threshold. |
| Date: | 2017-03-22 11:33:41 |
| Message-ID: | CA+Tgmob9=T8eDcLAJUPbTbfidfs-nc-NSH41fX_rm5bdEPHKpA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Mar 21, 2017 at 8:18 PM, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
>> Not only might that be unnecessary, but if we don't have a test
>> demonstrating the problem, we also don't have a test demonstrating
>> that a given approach fixes it.
>
> Preventing recycling from happening until we feel like it is probably
> fine. It is not fine to break it forever, though. The specific problem
> is that there is an XID stored in dead B-Tree + SP-GiST pages that is
> used in the subsequent RecentGlobalXmin interlock that determines if
> recycling is safe (if there is no possible index scan that could land
> on the dead page). You know, the _bt_page_recyclable() check.
Oh. OK, so this is not just about bloat -- it's about whether this
can be safely done at all. Somehow, I missed that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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