| From: | Kevin Grittner <kgrittn(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Kevin Grittner <kgrittn(at)postgresql(dot)org>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, "pgsql-committers(at)postgresql(dot)org" <pgsql-committers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold < |
| Date: | 2016-06-15 18:56:39 |
| Message-ID: | CACjxUsNAAA0QiS0vXJLkcaiyXz_4gWf4kThrwHr-iBFZU6F4hg@mail.gmail.com |
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| Lists: | pgsql-committers pgsql-hackers |
On Wed, Jun 15, 2016 at 1:50 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> The expression index case is the one to worry about; if there is a
> problem, that's where it is. What bothers me is that a function used
> in an expression index could do anything at all - it can read any
> table in the database.
It *can*, but then you are lying to the database when you call it
IMMUTABLE. Such an index can easily become corrupted through
normal DML. Without DML the ANALYZE has no problem. So you seem
to be concerned that if someone is lying to the database engine to
force it accept a function as IMMUTABLE when it actually isn't, and
then updating the referenced rows (which is very likely to render
the index corrupted), that statistics might also become stale.
They might.
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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