maria-developers team mailing list archive

[Sergei Petrunia <psergey@xxxxxxxxxxxx>]

Hi Elena,

I need testing for MWL#182 SHOW EXPLAIN. 

The code is here: lp:~maria-captains/maria/5.3-show-explain2 (note the '2' at
the end)

The branch is currently based on 5.3, although will move to 5.5 soon (I suppose
this doesn't cause any problems for testing).  

Currently, I can think of two things that need testing:

=== "Asynchronous Procedure Call" module === 
This is a module that allows one thread to schedule a call in the other thread,
and wait until the call has been invoked.

Suggested way to test: 
- run a set of queries that look at each other with "SHOW EXPLAIN FOR <thread>" 
  statements. 
- have some "victim" threads which run long queries, and have "attacker"
  threads which submit a lot of "SHOW EXPLAIN FOR <victim_thread>" queries.

=== On-the-fly EXPLAIN printing functionality ===
Before this WL, the code that produced EXPLAIN output 
- Required that optimizer produces a slightly different structures when EXPLAIN
  is running
- Did destructive modifications to the query plan (that is, it was not possible
  to call these functions two times to get two EXPLAIN outputs for the same
  planned query)

Suggested way to test:
- Run various complicated queries, with UNIONs, JOINs, etc. 
- While they are running, do SHOW EXPLAIN FOR command for them, expecting 
  it to crash or produce nonsensical output at some point.
  If SHOW EXPLAIN crashes, the crash report will show the query it was trying
  to obtain the EXPLAIN for.

My current suggestion is to use some "runner" threads to run the queries and 
use another set of threads to hit the "runner" threads with SHOW EXPLAIN
request.

When creating tests in mysql-test/t/show_explain.test, I made a framework that
allows to stop query execution at some particular point and then wait until
some number of SHOW EXPLAIN requests were arrived and served.

This requires insertion of "probes" into the source code, though.

Perhaps, we could use something like that for your testing: to have the query
pause at some "interesting" points and wait for SHOW EXPLAIN requests to arrive
and be served.  I wasn't able to come up with any intelligent way to find
interesting point though, so this is still just an idea.

BR
 Sergei
-- 
Sergei Petrunia, Software Developer
Monty Program AB, http://askmonty.org
Blog: http://s.petrunia.net/blog