Re: Transaction Snapshots and Hot Standby

Simon Riggs <simon@2ndQuadrant.com> writes:

> 3. Ignore problem
> Effects:
> * Long running queries on standby...
>    Have no effect on primary
>    Do not delay apply of WAL records on standby
> * Queries on standby give inconsistent answers in some cases, though
> doesn't generate any messages to show inconsistency occurred. Acceptable
> for read-only and insert only tables only.

This seems like a non-starter. 

Your comment about read-only and insert-only tuples only seems to make sense
if you assume there are other tables being updated simultaneously. Otherwise
of course there would be no WAL records for tuple removals.

In that case the problem is dealing with different usage patterns on different
tables. There might be a way to solve just that use case such as deferring WAL
records for those tables. That doesn't guarantee inter-table data consistency
if there were other queries which read from those tables and updated other
tables based on that data though. Perhaps there's a solution for that too
though.

--  Gregory Stark EnterpriseDB          http://www.enterprisedb.com Ask me about EnterpriseDB's RemoteDBA services!