The explain-plan tag has no wiki summary.
3
votes
2answers
315 views
Help to understand explain plan in Oracle
I am running a query in some big tables, and although it runs fine even tough is a lot of data, I'd like to understand what part of it weighs on the execution. Unfortunately I am not too good with ...
3
votes
1answer
215 views
Measuring the relative performance of queries given the assertion that “cost” isn't reliable
The cost field is a comparative cost that is used internally to determine the best cost for particular plans. The costs of different statements are not really directly comparable.
Source
Does ...
2
votes
1answer
144 views
Query results in a strange explain output
So I have a medium sized query that hits 15 tables. The query takes 36 sec on MySQL to complete. I ran EXPLAIN on the query and one of the tables returned this.
'1', 'SIMPLE', 'mount_adapters', ...
3
votes
1answer
297 views
Oracle explain for cascading delete is wrong
My deletes in Oracle 11 are very slow. The tables are linked by foreign keys and every foreign key constraint has a delete cascade set on it.
If I hit the explain button on a statement like this ...
1
vote
1answer
557 views
Postgres multiple joins slow query, how to store default child record
Ive got a small database in Postgres, about 10,000 records storing company customers.
I have a "slow" performing query (about half a second) which is performed very frequently, and my boss wants me to ...
5
votes
1answer
370 views
Execution plan using B+ tree index, but also sorts
I'm using Oracle sqlplus. And I have the following query:
SELECT fooID from foo MINUS
SELECT fooID from bar;
I have created two unclustered B+ tree indexes. One in the field fooIDof the table foo ...
2
votes
2answers
742 views
Understanding time format of the EXPLAIN command - Postgres
When I run the EXPLAIN ANALYZE command on a given query, I'm having a difficult time interpreting the outputted time value. For example (actual time=8163.890..8163.893). Do the internal decimals ...
5
votes
1answer
731 views
Oracle concatenation of queries and function index usage
I have a problem with something I can't understand about indexes in Oracle 11g.
We can create test data with:
create table test2(field1 varchar2(100),field2 varchar2(100),field3 number,field4 ...
1
vote
1answer
697 views
What does TBSCAN GENROW mean in Explain Plan?
In a DB2 Explain Plan, what does TBSCAN GENROW (line 5 below) mean?
SELECT STATEMENT ( Estimated Costs = 1.811E+03 [timerons] )
1 RETURN
2 NLJOIN
3 [O] TBSCAN
4 SORT
...
6
votes
2answers
111 views
Is there a good “rule of thumb” for translating EXPLAIN cost to (wall-clock) runtime?
From time to time, consumers of my database processes will ask for an estimate of when a given task will be done. While I feel like I know how to read an EXPLAIN in most database engines, I have ...
1
vote
1answer
331 views
What does HSJOIN mean in an Explain Plan?
I have the following EXPLAIN PLAN results from a query on my DB2 database.
0 SELECT STATEMENT ( Estimated Costs = 5.928E+02 [timerons] )
1 RETURN
2 HSJOIN
3 [O] ...
