Re: Reads Block Writes?

From: Howard J. Rogers <dba_at_hjrdba.com>
Date: Tue, 4 Jun 2002 05:59:12 +1000
Message-ID: <adghqv$dl5$1@lust.ihug.co.nz>

"Buck Turgidson" <jc_va_at_hotmail.com> wrote in message news:53bf207579c6f09f7c05b678b7bb15f5.38849_at_mygate.mailgate.org...
> I know that a "select for update" will lock rows and block an update
> statement, but is it possible for a simple select to block an update of
> the same table? Using a "lockby" script, it appears to be the case that
> a long running select is blocking an update, but I didn't think that
> this would happen.

It doesn't. Ever.

A regular select takes no locks whatsoever, generates no redo, no undo, and therefore cannot block other readers and writers.

It is, however, possible that a large report could chew up all available temporary tablespace and prevent another large report that needs to sort in that tablespace from completing successfully -but you'd know about that because of the rash of error messages produced.

Regards
HJR
>
> Thanks for any replies.
>
>
>
> --
> Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
Received on Mon Jun 03 2002 - 14:59:12 CDT