| From: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Thom Brown <thom(at)linux(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Proposal: "Causal reads" mode for load balancing reads without stale data |
| Date: | 2016-03-25 00:28:18 |
| Message-ID: | CAB7nPqR-mcswK38h6ce4Ezy36VhtEDV3uix74MJf_yaMiy7UBA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Mar 24, 2016 at 11:20 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Mar 24, 2016 at 2:11 AM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com> wrote:
>> - SyncRepWaitForLSN(gxact->prepare_end_lsn);
>> + SyncRepWaitForLSN(gxact->prepare_end_lsn, false);
>> Isn't it important to ensure that a PREPARE LSN is applied as well on
>> the standby with remote_apply? Say if an application prepares a
>> transaction, it would commit locally but its LSN may not be applied on
>> the standby with this patch. That would be a surprising behavior for
>> the user.
>
> You need to wait for COMMIT PREPARED, but I don't see why you need to
> wait for PREPARE itself.
Multi-master conflict resolution. Knowing in-time that a prepared
transaction has been applied is useful on another node for lock
conflicts resolution. Say a PRIMARY KEY insert is prepared, and we
want to know at application level that its prepared state is visible
everywhere.
--
Michael
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