I had a customer who complains about performance issues on one of the oracle production database. Environment Oracle Database 12c R1 (12.1.0.2) on Linux with Oracle RAC (two nodes). To start with, I collected some AWR reports around the complain time, and I found the top wait events (most of the time) as follows: So, … Continue reading Oracle Database Performance Issue: High waits for “PX Deq: Slave Session Stats”
Oracle Database 12c: Performance Management – Question 20
Formatting a Wrapped Execution Plan
If you received or produced an execution plan like the following unreadable one: ---------------------------------------------------------------------------------------------------| Id | Operation | Name | E-Rows | OMem |1Mem | Used-Mem |---------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | || || 1 | SORT AGGREGATE | | 1 | || ||* 2 | HASH JOIN | | 13 | 1102K|1102K| … Continue reading Formatting a Wrapped Execution Plan
Why Query is not using the Index?
This post answers the following specific question: Why “distinct query” is not using the index (in some cases)? Let us try the following test case: Create sample table “t_distinct” and add an index to the “ID” column and collect statistics for table and index: Let us run the following basic query: It is clear … Continue reading Why Query is not using the Index?
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