Re: Clarification on a Time travel feature

[Hans-Juergen Schoenig <postgres(at)cybertec(dot)at>]

hello ...

i guess there is no formal proposal yet but there are some ideas around and some major challenges have been discussed already.

i think simon riggs was planning to work on it in the future.

the basic idea here is to have the option to create a "snapshot" which then stays in the database. the main challenge is that PostgreSQL

should not keep all version of a row since the snapshot but VACUUM should be able to clean out all rows which are not seen by any snapshot or any ongoing transaction.

this should be a quite fancy solution which is quite space efficient.

internally we had the idea of tweaking VACUUM a little:

VACUUM BEFORE timestamp;

and ...

SET current_snapshot TO '2007-10-10 ...';

this would allow a queries to use any snapshot after the timestamp defined by VACUUM (if data is around).

the downside here: you might potentially eat up more space.

flashback data should be read only, of course.

best regards,

hans

On Oct 31, 2007, at 11:31 AM, Gokulakannan Somasundaram wrote:

Hi,
   I went through the mailing list and couldn't get answer to the question.

a) Is there a proposal in place for going back in time within a transaction?



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Thanks,
Gokul.
CertoSQL Project,
Allied Solution Groups.
(www.alliedgroups.com)

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