On 03/05/2015 07:37 AM, inspector morse wrote:
I'm confused with what Igor said. He said to create the temporary table
with "on commit preseve rows" but in the documentation it states that
when a session ends (like after each request in a web application when
not using persistent connections), the temporary table would
automatically be dropped.
Just to test it, I created the following in a new session:
CREATE TEMPORARY TABLE http_querystring_values (key TEXT NOT NULL
PRIMARY KEY, value TEXT NOT NULL) ON COMMIT DELETE ROWS;
However, none of the other sessions can find this table. This is correct
according to the documentation.
Is there any reason why Postgresql does not implement the SQL standard's
version of GLOBAL temporary tables?
I also don't like the idea of passing the "state" around to functions.
I'd rather just query a table OR read some global variable. The JSON
/HSTORE syntax looks horrible, I just like to stick with the simplicity
of a table.
So create a permanent session table and assign session keys. Strangely
enough that is one of the ways Django(web framework does it):) I know
you want to build your set up, but this is a solved problem. It is
solved because people ran into the issues you already have encountered
and are yet to encounter and realized that common problems led to common
solutions. Given that you want to reinvent the wheel I would suggest
spending time looking at the other wheels out there and borrow from them.
On Thu, Mar 5, 2015 at 10:18 AM, Adrian Klaver
<adrian.kla...@aklaver.com <mailto:adrian.kla...@aklaver.com>> wrote:
On 03/05/2015 07:10 AM, Merlin Moncure wrote:
On Thu, Mar 5, 2015 at 8:58 AM, Igor Neyman
<iney...@perceptron.com <mailto:iney...@perceptron.com>> wrote:
From: pgsql-general-owner@__postgresql.org
<mailto:pgsql-general-ow...@postgresql.org>
[mailto:pgsql-general-owner@__postgresql.org
<mailto:pgsql-general-ow...@postgresql.org>] On Behalf Of
inspector morse
Sent: Thursday, March 05, 2015 9:21 AM
To: pgsql-general@postgresql.org
<mailto:pgsql-general@postgresql.org>
Subject: [GENERAL] Sharing data between stored functions?
I have written a simple web application using pure pl/pgsql
and so far it is
working really well (I find it quite easy to maintain as
well especially in
terms of form validation).
Basically, apache/php passes receives the incoming web
request and calls a
"serve_page" function in postgresql passing the querystring
and post values.
The serve_page declares 5 temporary tables to store
querystring values, post
values, validation messages, and general data that is going
to be shared
between the functions.
Then it parses the page url and calls the appropriate "page
render" stored
function.
Throughout the "building" the web page, several of the
temporary tables are
written too (about 20-30 rows total would be add to the
temporary table).
Once the page "html" is built, the temporary tables are
dropped and the HTML
is sent back to php to write to the response stream.
I read in the documentation that temporary tables can cause
catalog bloat or
performance issues.....in my context (where only 20-30 rows
are written
every request and the table is dropped after rending), could
it cause an
issue for many incoming requests?
You’d be better off not creating/dropping temp tables every
time.
Just create global temp tables once with “ON COMMIT PRESERVE
ROWS“ option,
and when any session uses them their contents will be
private to this
session.
maybe 'ON COMMIT DELETE ROWS' would be a better choice, depending on
the scenario: if the state is only valid for a requst, then you'd
clear the state at the end of the transaction.
GLOBAL temp tables are deprecated. I'm curious why, because
they are
so useful for this particular task.
Because they never existed:
http://www.postgresql.org/__docs/9.3/interactive/sql-__createtable.html#SQL-__CREATETABLE-COMPATIBILITY
<http://www.postgresql.org/docs/9.3/interactive/sql-createtable.html#SQL-CREATETABLE-COMPATIBILITY>
Compatibility
"The SQL standard also distinguishes between global and local
temporary tables, where a local temporary table has a separate set
of contents for each SQL module within each session, though its
definition is still shared across sessions. Since PostgreSQL does
not support SQL modules, this distinction is not relevant in PostgreSQL.
For compatibility's sake, PostgreSQL will accept the GLOBAL and
LOCAL keywords in a temporary table declaration, but they currently
have no effect. Use of these keywords is discouraged, since future
versions of PostgreSQL might adopt a more standard-compliant
interpretation of their meaning.
"
In plpgsql, it's also possible to maintain state by keeping it in
things like arrays of records that you pass around. In the
future we
might use jsonb for this I think.
merlin
--
Adrian Klaver
adrian.kla...@aklaver.com <mailto:adrian.kla...@aklaver.com>
--
Adrian Klaver
adrian.kla...@aklaver.com
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