Comments on: update account set password = ‘new_password’; oops?!

By: </depesz> » Blog Archive » rownum anyone? cumulative sum in one query?

Fri, 17 Aug 2007 08:40:41 +0000

[...] as you can see it’s pretty simple. one important thing is that i use custom variable class – you have to define it in your postgresql.conf. as for how – check my previous posting. [...]

By: depesz

depesz — Wed, 01 Aug 2007 04:55:13 +0000

@Xavier:
that’s why there is before statement trigger.

i really think it would be good if you just tried the code. the problem you’re describing doesn’t exist.

By: Xavier

Xavier — Tue, 31 Jul 2007 18:36:12 +0000

No, I don’t _want_ to do that, I’m just saying that $_SHARED{‘count’} will reference to the same variable across all three tables’ UPDATE statements, and so it could be a problem.

By: depesz

depesz — Tue, 31 Jul 2007 18:00:54 +0000

@Xavier:
no, it doesn’t block the transaction. nor it was ever supposed to do so.
it is to block multi-row-updates. not multi-row-updateing-transactions.

if you want to block something like this, it’s doable – let me know, i’ll write it. on the other hand – i don’t really see the point of blocking such transactions.

By: Xavier

Xavier — Tue, 31 Jul 2007 16:43:39 +0000

I haven’t tested that technique yet, but it looks as if it would block transactions trying to update just one row in multiple tables to which the triggers are bound.

For example, if you bind these triggers to 3 tables (in order to protect them from mass-updates), and initiate a transaction, calling:
BEGIN;
UPDATE table1 SET field1 = val1 WHERE id = 1;
UPDATE table2 SET field2 = val2 WHERE id = 2;
UPDATE table3 SET field3 = val3 WHERE id = 3;
COMMIT;

I would expect it to die since it uses a shared counter for the trigger function. It would probably be better to create a hash-table to store one counter per table, and use the table-name as a hash key so you are preventing this.

By: depesz

depesz — Tue, 31 Jul 2007 05:35:16 +0000

@krolik:
not really. if it’s a tribute, then it’s rather tribute to some anonymous (for me) soul from “tbg” which was setting “vacation” lately.

By: krolik

krolik — Mon, 30 Jul 2007 20:50:47 +0000

Depesz: tribute to morr’s mailsystem disaster ?

By: Jakob

Jakob — Mon, 30 Jul 2007 14:57:18 +0000

This is exactly what I expected to find out after reading the title o.us poetry. Thanks for informative article

By: depesz

depesz — Fri, 27 Jul 2007 14:14:23 +0000

thanks – i think i fixed then/than issue.

By: Krzysztof Wilczynski

Krzysztof Wilczynski — Fri, 27 Jul 2007 11:58:15 +0000

Excellent piece of code… thanks. By the way: sed ‘s/then/than/’;