合并、分区和远程数据库 - 性能调优 Oracle

Question

I want to tune my merge query which inserts and updates table in Oracle based on source table in SQL Server. Table Size is around 120 million rows and normally around 120k records are inserted/updated daily. Merge takes around 1.5 hours to run. It uses nested loop and primary key index to perform insert and update. There is no record update date in source table to use; so all records are compared.

Merge abc tgt
using
(
   select a,b,c
   from sourcetable@sqlserver_remote) src
  on (tgt.ref_id = src.ref_id)
when matched then 
update set 
      .......
where 
    decode(tgt.a, src.a,1,0) = 0
     or ......

when not matched then 
insert (....) values (.....);
commit;

Since the table is huge and growing every day, I partitioned the table in DEV based on ref id (10 groups) and created local index on ref id. Now it uses hash join and full table scan and it runs longer than the existing process. When I changed from local to global index (ref_id), i uses nested loops but still takes longer to run than the existing process.

Is there a way to performance tune the process.

Thanks...

Answer 1

I'd be wary to join/merge huge tables over a database link. I'd try to copy over the complete source table (for instance with a non-atomic mview, possibly compressed, possibly sorted, certainly only the columns you'll need). After gathering statistics, I'd merge the target table with the local copy. Afterwards, the local copy can be truncated.

I wouldn't be surprised, if partitioning speeds up the merge from the local copy to your target table.