Join Permutations Heatmaps
Generating heatmaps for join permutations using Python Continue Reading
cost based optimizer
Correlated Subqueries in the SELECT Clause (2)
Examples where Oracle optimizer doesn’t unnest subqueries in the SELECT clause Continue Reading
Correlated Subqueries in the SELECT Clause
How Oracle and SQL Server optimize correlated subqueries in the SELECT clause with an example how to manually optimize such queries for Oracle. Continue Reading
Tracking the Optimizer with gdb
Tracing a low-level Oracle C function for getting insights into the optimizer decision making Continue Reading
Enriching Trace with Call Stacks
A DTrace script for capturing the call stack when a line gets written into the trace file. It’s useful, for example, for finding out the functions participating in a particular query transformation. Continue Reading
Suboptimal Execution Plan with Join Predicate Push-Down Transformation
JPPD is performed where it shouldn’t. Use the CBO trace parser for detecting the problem. Continue Reading
Dissecting Cost Based OR-Expansion
Analyzing the CBO trace for getting insight into the cost based OR-expansion Continue Reading
Fast Retrieval of DYNAMIC_SAMPLING_RESULT Information
Correlating an active dynamic sampling trace with the data dictionary Continue Reading
first_rows Optimization in Uncorrelated Subqueries
Suboptimal execution plans can be generated for uncorrelated subqueries involved in set operations. Continue Reading
Join Cardinality Misestimate (“Adjustment-to-Zero Issue”) in Oracle 12.2 – Part 2
Enhanced example of join cardinality misestimate caused by adjustment-to-zero issue Continue Reading