Multiple SELECTs cached by Postgres?

#31

Johannes Bauer <dfnsonfsduifb (AT) gmx (DOT) de> wrote:

Quote:

now() is docmented as the transaction start time, so theres no caching
and inside the same transaction its result should always be the same value.

For resolving performance questions EXPLAIN gives You valuable insight.

Oh yes, I forget to mention: I tried EXPLAIN, but it returns the same
search tree twice. However I do not know if EXPLAIN knows about caching
and would display that. Therefore I think that maybe the queries might
be cached although EXPLAIN states there is a (for example) seq search.

There is no result caching in PostgreSQL.

I think that would be difficult - it could be that some other transaction
has modified the database between the first and the second time the query
is issued.
How should the server determine if a concurrent change to the database has
invalidated the first result?

Yours,
Laurenz Albe

#32

Johannes Bauer <dfnsonfsduifb (AT) gmx (DOT) de> wrote:

Quote:

now() is docmented as the transaction start time, so theres no caching
and inside the same transaction its result should always be the same value.

For resolving performance questions EXPLAIN gives You valuable insight.

Oh yes, I forget to mention: I tried EXPLAIN, but it returns the same
search tree twice. However I do not know if EXPLAIN knows about caching
and would display that. Therefore I think that maybe the queries might
be cached although EXPLAIN states there is a (for example) seq search.

There is no result caching in PostgreSQL.

I think that would be difficult - it could be that some other transaction
has modified the database between the first and the second time the query
is issued.
How should the server determine if a concurrent change to the database has
invalidated the first result?

Yours,
Laurenz Albe

#33

Johannes Bauer <dfnsonfsduifb (AT) gmx (DOT) de> wrote:

Quote:

now() is docmented as the transaction start time, so theres no caching
and inside the same transaction its result should always be the same value.

For resolving performance questions EXPLAIN gives You valuable insight.

Oh yes, I forget to mention: I tried EXPLAIN, but it returns the same
search tree twice. However I do not know if EXPLAIN knows about caching
and would display that. Therefore I think that maybe the queries might
be cached although EXPLAIN states there is a (for example) seq search.

There is no result caching in PostgreSQL.

I think that would be difficult - it could be that some other transaction
has modified the database between the first and the second time the query
is issued.
How should the server determine if a concurrent change to the database has
invalidated the first result?

Yours,
Laurenz Albe

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Multiple SELECTs cached by Postgres?

comp.databases.postgresql comp.databases.postgresql

Re: Multiple SELECTs cached by Postgres? - 09-08-2008 , 02:14 AM

Re: Multiple SELECTs cached by Postgres? - 09-08-2008 , 02:14 AM

Re: Multiple SELECTs cached by Postgres? - 09-08-2008 , 02:14 AM