Category Archives: Uncategorized

I’ve been working for hours on a performance issue the past week and this one and found a strange situation:  A new function based index sped up the queries that used it, but slowed down other queries that didn’t use … Continue reading →

I thought that an invisible index was never queried, but that it was only maintained as the table was modified.  But, when you use the dbms_stats package to gather statistics on a table, including its indexes, the invisible indexes are … Continue reading →

We ran into a performance issue where all of the top queries in our AWR report were doing a LIKE comparison of a NUMBER column against a character literal like this: customer_number LIKE ‘123456%’ customer_number is a selective predicate and … Continue reading →

I’m still doing state dumps as described in my previous post. I wanted to collect the state dumps (diag process trace files) from all nodes of my Exadata database and decided to write a couple of scripts to automate it … Continue reading →

One of my favorite children’s books when my children were younger was one about the Berenstain Bears where Father Bear tries to teach his son how to ride a bike and keeps making all these dumb mistakes.  “Let that be … Continue reading →

Oracle support recommends setting the hidden parameter _unnest_subquery to FALSE to improve the performance of PeopleSoft applications on Oracle databases.  I’m trying to understand the consequence of changing this parameter from its default setting of TRUE. PeopleSoft applications have a … Continue reading →

In an earlier post I described the process that I go through to check the plans of production SQL queries to see if they change when you do a system upgrade or patch.  Today I’ve been following that process to … Continue reading →

We usually use locally partitioned indexes on partitioned tables.  Many of our data warehouse tables are partitioned by date and partitions get added or removed over time.  It is much easier to maintain the indexes on this kind of table … Continue reading →

I’ve uploaded a sql script that gets an AWR report for yesterday, a week from yesterday, and four weeks from yesterday for the same time period – 10 am to 4  pm. I’ve been manually reviewing the previous day’s AWR … Continue reading →

I’m helping a coworker learn how to do Oracle performance tuning and today I think we found some good documentation on which V$ views to use for tuning which can also help with reading an AWR report.  In a previous … Continue reading →