Snapshot Materialized Views - GSoC

2010/5/20 Pavel <baros.p@seznam.cz>:

d) what to do when someone use INSERT, UPDATE or DELETE against MV?
  1 - raise error? - I prefer this option

+1, FWIW

  2 - let commands change MV? (no chance to let changes propagate to
source tables, not for this summer :)
  if pg lets user to DML against MV, I expect that triggers should work too

no, if you don't propagate then you don't have a view of the tables
the MV comes from...
error if you'll not implement propagation now

--
Jaime Casanova www.2ndQuadrant.com
Soporte y capacitación de PostgreSQL

2010/5/20 Pavel <baros.p@seznam.cz>:

For this summer I have plan to make patch inplementing snapshot materialized
views (MV). I believe it will not be end of effort to implement more of MV.
But I / we need discuss MV syntax and exact behaviour so I have some
questions about that for all of you:

a) relkind for materialized view in pg_class?
  - I'm voting for char 'm' quite obvious why, but not sure about alias:
    1 - RELKIND_MVIEW
    2 - RELKIND_MATVIEW
       or any other ideas?

I think the prior question is whether we need to create a new relkind
at all. I'm prepared to believe that the answer is yes, but I'd like
to see a clear justification of why we can't use either 'v' or 'r'.
It seems to me that a materialized view is a lot like a regular old
table with a special rewrite rule attached to it somewhere.

b) create MV syntax?
  - CREATE MATERIALIZED VIEW mvname AS ..., I think it is quite
obvious to do so, but I had to ask

I think that's OK.

c) refresh command syntax?
    1 - ALTER MATERIALIZED VIEW mvname REFRESH
    or
    2 - REFRESH MATERIALIZED VIEW mvname

1.

d) what to do when someone use INSERT, UPDATE or DELETE against MV?
  1 - raise error? - I prefer this option
  2 - let commands change MV? (no chance to let changes propagate to
source tables, not for this summer :)
  if pg lets user to DML against MV, I expect that triggers should work too

1.

e) what to do when someone drop table or column?
 - it behave like it was a classic view. Fire error and hint
 - CASCADE option will remove MV

Agree.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company

Pavel,

b) create MV syntax?

- CREATE MATERIALIZED VIEW mvname AS ..., I think it is quite
obvious to do so, but I had to ask

please do not fortget the:

create or replace MATERIALIZED VIEW

option.

And also the

DROP if exists

for the drop-command

Best wishes

Harald

--
GHUM Harald Massa
persuadere et programmare
Harald Armin Massa
Spielberger Straße 49
70435 Stuttgart
0173/9409607
no fx, no carrier pigeon
-
Using PostgreSQL is mostly about sleeping well at night.

"Massa, Harald Armin" <chef@ghum.de> writes:

please do not fortget the:
create or replace MATERIALIZED VIEW
option.

Please do. For something as complex as a table or view, CREATE OR
REPLACE is a lot more complicated than it is for simple objects like
functions. (See flamewar just a couple weeks ago about C.O.R. vs
CREATE IF NOT EXISTS for tables.) Putting this on the to-do list
for the GSOC project will just about guarantee failure. It's most
likely too large a task for a GSOC project already...

regards, tom lane

On May 21, 2010, at 15:59 , Robert Haas wrote:

2010/5/20 Pavel <baros.p@seznam.cz>:

For this summer I have plan to make patch inplementing snapshot materialized
views (MV). I believe it will not be end of effort to implement more of MV.
But I / we need discuss MV syntax and exact behaviour so I have some
questions about that for all of you:

a) relkind for materialized view in pg_class?
- I'm voting for char 'm' quite obvious why, but not sure about alias:
1 - RELKIND_MVIEW
2 - RELKIND_MATVIEW
or any other ideas?

I think the prior question is whether we need to create a new relkind
at all. I'm prepared to believe that the answer is yes, but I'd like
to see a clear justification of why we can't use either 'v' or 'r'.
It seems to me that a materialized view is a lot like a regular old
table with a special rewrite rule attached to it somewhere.

I guess the justification is that with the same argument you could argue that a view should have relkind 'r', since it's just an empty table with a rewrite rule attached. I think relkind is mostly there to make pg_dump's and the information schema's job easier - without it, distinguishing tables with ON SELECT rules from views seem rather AI-complete. The same holds for materialized views vs. tables and materialized views vs. views.

best regards,
Florian Pflug

On fre, 2010-05-21 at 16:31 +0200, Florian Pflug wrote:

I guess the justification is that with the same argument you could
argue that a view should have relkind 'r', since it's just an empty
table with a rewrite rule attached.

It used to be that way, but now a view doesn't have an empty table
attached to it, but no table at all. Hence the different relkind.