Re: Overhead cost of Serializable Snapshot Isolation

On Wed, Oct 12, 2011 at 6:34 AM, Heikki Linnakangas
<heikki.linnakangas@enterprisedb.com> wrote:
> On 11.10.2011 23:21, Simon Riggs wrote:
>>
>> If the normal default_transaction_isolation = read committed and all
>> transactions that require serializable are explicitly marked in the
>> application then there is no way to turn off SSI without altering the
>> application. That is not acceptable, since it causes changes in
>> application behaviour and possibly also performance issues.
>
> I don't get that. If all the transactions that require serializability are
> marked as such, why would you disable SSI for them? That would just break
> the application, since the transactions would no longer be serializable.
>
> If they don't actually need serializability, but repeatable read is enough,
> then mark them that way.

Obviously, if apps require serializability then turning
serializability off would break them. That is not what I have said,
nor clearly not what I would mean by "turning off SSI".

The type of serializability we had in the past is now the same as
repeatable read. So the request is for a parameter that changes a
request for serializable into a request for repeatable read, so that
applications are provided with exactly what they had before, in 9.0
and earlier.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services