Snapshot replication slow during purge of master table

Question

I have basic snapshot/materialized view replication of a big table (around 6 million rows).
The problem that I run into is that when I run a purge of the master table at the master site (delete dml), the snapshot refresh time becomes slower. After the purge the snapshot refresh time goes back to the normal time interval.
I had thought that the snapshot does a simple select so any exclusive lock on the table should not hinder the performance.
Has anyone seen this problem before and if so what has been the workaround?
The master site and the snapshot site both are 8.1.7.4 and are both unix tru64.
I don't know if this has any relevence but the master database is rule based while the snapshot site is cost based.
thanks in advance

Answer 1

Hello Alan,
Your problem is, to know inside a table-trigger if the actual DML was caused
by a replication or a normal local DML.
One way (I'm practising) to solve (in Oracle 8.1.7) this is the following:
You can use in the trigger code the functions DBMS_SNAPSHOT.I_AM_A_REFRESH(),
DBMS_REPUTIL.REPLICATION_IS_ON() and DBMS_REPUTIL.FROM_REMOTE()
(For details see oracle documentation library)
For example: a trigger (before insert of each row) at the master side
on a table which is an updatable snapshot:
DECLARE
     site_x VARCHAR2(128) := DBMS_REPUTIL.GLOBAL_NAME;
     timestamp_x      DATE;
     value_time_diff     NUMBER;
BEGIN
IF (NOT (DBMS_SNAPSHOT.I_AM_A_REFRESH) AND DBMS_REPUTIL.REPLICATION_IS_ON) THEN
IF NOT DBMS_REPUTIL.FROM_REMOTE THEN
IF inserting THEN
     :new.info_text := 'Hello table; this entry was caused by local DML';
END IF;
END IF;
END IF;
END;
By the way: I've got here at work nearly the same configuration, now in production since a year.
Kind regards
Steffen Rvckel