| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com> |
| Cc: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Peter van Hardenberg <pvh(at)pvh(dot)ca>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Patch: Implement failover on libpq connect level. |
| Date: | 2016-11-16 13:50:22 |
| Message-ID: | CA+TgmoZVxSoHt_4TJGW7kU9bNad5GX-n9C0-4zsm345665Qm8Q@mail.gmail.com |
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| Lists: | pgsql-hackers pgsql-jdbc |
On Tue, Nov 15, 2016 at 11:31 PM, Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com> wrote:
>> > So I am tempted to just
>> > hold my nose and hard-code the SQL as JDBC is presumably already
>> doing.
>
> JDBC is sending "show transaction_read_only" to find whether it is master or
> not.
> Victor's patch also started with it, but later it was transformed into
> pg_is_in_recovery
> by him as it appeared more appropriate to identify the master / slave.
Hmm, let's go back to the JDBC method, then. "show
transaction_read_only" will return true on a standby, but presumably
also on any other non-writable node. You could even force it to be
true artificially if you wanted to force traffic off of a node, using
ALTER {SYSTEM|USER ...|DATABASE ..} SET default_transaction_read_only
= on
I think that would address Alvaro's concern, and it's nicer anyway if
libpq and JDBC are doing the same thing.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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