Query running much slower after about 100000 rows inserted in the source table

I've a stored procedure which runs every hour to insert about 1000 rows to Table A and then a query will be executed against this table and insert into Table B . It costs about 2 mins to run normally but it will always run much slower to take about 24 hours to complete every 7 days. What I can do now is copy data in Table A  to a temp Table, recreate Tabla A from the temp Table, the procedure will then run normally.

I've checked that although the query is a little bit complex but it hits the Index and the consitent/physical gets are almost the same with the two (normal/slower) situations.

What else should I solve for this dilemma?

It really bothers me for a long long time?

PS: There're about 500000 rows in Table A and B. Received on Sat Feb 22 2003 - 21:49:18 CST