On 25/07/2014 06:46, brucedickin...@wp.pl [firebird-support] wrote:
Hi,
1. I've deleted 500000 records from TABLE A. I've commited transaction.
2. I made SELECT * FROM TABLE A. Transaction was starting for a very
long time.
I just wanted to make sure that there is no way to prevent this
behaviour? I mean, I can not delay somehow clearing of this garbage?
As far as I understand this article:
http://www.firebirdsql.org/manual/gfix-housekeeping.html
there is no such possibility becasue:
"Whenever a subsequent transaction reaches garbage from a /committed/
transaction, that garbage is automatically cleared out."
So it appears. Essentially part of the cost of doing the deletion is
palmed off onto some later user, who is faced with unpredictable delays
in consequence. For example an overnight housekeeping job can result in
the first end user transaction of the day taking orders of magnitude
longer than usual (and timing out and crashing, if its timeouts are set
to something reasonable).
You can avoid this cost being passed onto the poor user who through no
fault of his own is the first to follow the housekeeping by including
the "SELECT * FROM TABLEA" as part of the cleanup job, thus putting the
cost back with its owner. In other words you can't delay the garbage
collection, but you can make it happen earlier so that it's predictable.
--
Tim Ward
