On 20.12.2017 16:12, Laurenz Albe wrote:
Konstantin Knizhnik wrote:
I wonder if Postgres community is interested in supporting time travel
queries in PostgreSQL (something like AS OF queries in Oracle:
https://docs.oracle.com/cd/B14117_01/appdev.101/b10795/adfns_fl.htm).
As far as I know something similar is now developed for MariaDB.
I think that would be a good thing to have that could make
the DBA's work easier - all the requests to restore a table
to the state from an hour ago.
Please notice that it is necessary to configure postgres in proper way in order to be able to perform time travels.
If you do not disable autovacuum, then old versions will be just cleaned-up.
If transaction commit timestamps are not tracked, then it is not possible to locate required timeline.
So DBA should make a decision
in advance whether this feature is needed or not.
It is not a proper instrument for restoring/auditing existed database which was not configured to keep all versions.
May be it is better to add special configuration parameter for this feature which should implicitly toggle autovacuum and track_commit_timestamp parameters).
The obvious drawbacks of keeping all versions are
1. Increased size of database.
2. Decreased query execution speed because them need to traverse a lot of not visible versions.
So may be in practice it will be useful to limit lifetime of versions.
I failed to support AS OF clause (as in Oracle) because of shift-reduce
conflicts with aliases,
so I have to introduce new ASOF keyword. May be yacc experts can propose
how to solve this conflict without introducing new keyword...
I think it would be highly desirable to have AS OF, because that's
the way the SQL standard has it.
Completely agree with you: I just give up after few hours of attempts to make bison to resolve this conflicts.
Yours,
Laurenz Albe
--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
