This is just a short blog post about a simple DTrace script (dtrace_kghal_pga_code), that i recently wrote and published due to a PGA memory leak troubleshooting assignment. A client of mine noticed a major PGA memory increase after upgrading to Oracle 12c. The PL/SQL code did not change - just the database release. He already troubleshooted the issue with help of Tanel Poder's blog post "Oracle Memory Troubleshooting, Part 4: Drilling down into PGA memory usage with V$PROCESS_MEMORY_DETAIL" and identified the corresponding heap and allocation reason.
This blog post is inspired by a question from an attendee of Sigrid Keydana's DOAG 2015 conference session called "Raising the fetchsize, good or bad? Exploring memory management in Oracle JDBC 12c". Basically it was a question about what the wait event "SQL*Net more data to client" represents and what it really measures. In general you may use the following steps, if you don't know what a particular wait event means:
The idea for this blog post started a few weeks ago when i had to troubleshoot some Oracle database / SQL performance issues at client site. The SQL itself included several views and so placing hints (for testing purpose) into the views was not possible, especially as the views were used widely and not only by the SQL with the performance issue. In consequence this blog post is about the difference between embedded global and local hints and how to use them.
This is a short blog post about another query transformation (check my first blog post [Oracle] DB Optimizer Part VIII - Looking under the hood of query transformation (done by CBO) with simple real life example first, if you never heard of the term "query transformations"), that fixes a cardinality estimation issue with multiple (OR) predicates that cover the whole data range. I have to admit that this is a special case, but it can happen as observed by my client
This release is just a quick bug fix release of an older 1.1.1 version of the plug-in. It’s long overdue but I’ve managed to fix “” problem only couple weeks ago. I’ve distributed the new version to the folks who have reached out to me by email of via blog reporting the issue in the [...]