On 12th of December, Tom Lane committed patch:
Improve EXPLAIN to print the grouping columns in Agg and Group nodes. Per request from Kevin Grittner.
Tag: explain
explain.depesz.com – update, new (great!) feature
I just updated explain.depesz.com – my tool for analysis of explain analyze plans.
New feature is: you can now create accounts.
Continue reading explain.depesz.com – update, new (great!) feature
Explaining the unexplainable – part 5
In previous posts in this series, I talked about how to read EXPLAIN output, and what each line (operation/node) means.
Now, in the final post, I will try to explain how it happens that Pg chooses “Operation X" over “Operation Y".
Explaining the unexplainable – part 4
In this, hopefully 2nd to last, post in the series, I will cover the rest of usually happening operations that you can see in your explain outputs.
Explaining the unexplainable – part 3
In previous post in the series I wrote about how to interpret single line in explain analyze output, it's structure, and later on described all basic data-getting operations (nodes in explain tree).
Today, we'll move towards more complicated operations.
Explaining the unexplainable – part 2
Last time I wrote about what explain output shows. Now I'd like to talk more about various types of “nodes" / operations that you might see in explain plans.
Explaining the unexplainable
One of the first things new DBA hears is “Use the EXPLAIN". And upon first try he/she is greeted with incomprehensible:
QUERY PLAN --------------------------------------------------------------------------------------------------------------------------- Sort (cost=146.63..148.65 ROWS=808 width=138) (actual TIME=55.009..55.012 ROWS=71 loops=1) Sort KEY: n.nspname, p.proname, (pg_get_function_arguments(p.oid)) Sort Method: quicksort Memory: 43kB -> Hash JOIN (cost=1.14..107.61 ROWS=808 width=138) (actual TIME=42.495..54.854 ROWS=71 loops=1) Hash Cond: (p.pronamespace = n.oid) -> Seq Scan ON pg_proc p (cost=0.00..89.30 ROWS=808 width=78) (actual TIME=0.052..53.465 ROWS=2402 loops=1) FILTER: pg_function_is_visible(oid) -> Hash (cost=1.09..1.09 ROWS=4 width=68) (actual TIME=0.011..0.011 ROWS=4 loops=1) Buckets: 1024 Batches: 1 Memory Usage: 1kB -> Seq Scan ON pg_namespace n (cost=0.00..1.09 ROWS=4 width=68) (actual TIME=0.005..0.007 ROWS=4 loops=1) FILTER: ((nspname <> 'pg_catalog'::name) AND (nspname <> 'information_schema'::name))
What does it even mean?
Changes on explain.depesz.com
So, I made some changes to explain.depesz.com, and while informing about it, I'd like to brag a bit about numbers, again 🙂
Changes on explain.depesz.com
Today there were some changes on explain.depesz.com – a bugfix, and functionality improvement.
Changes on explain.depesz.com
One of the features that is actually disliked is anonymization. But, regardless of the dislike – it has some users. And one of the user mailed me with information about a bug – namely – foreign table file names were not anonymized.
So, I wrote a patch, tests, released new version of underlying parsing library.