Sunday, January 27, 2013

Fun with Bugs, Issue #3, January 2013

This week in my posts on Facebook I paid attention mostly to bugs in MySQL 5.6.x, as I really expected to see 5.6 GA announcement soon. Maybe some of the bugs were the reason to postpone release a bit. Anyway, let's start with serious bug reports and some trends I've noted.

I've noted that some of "Verified" bug reports somehow silently miss comments about their status in MySQL 5.6. Check Bug #68137, for example. It is repeatable on 5.5.31 (yet to be released, but it means 5.5.30 is cloned off and will be released soon) and 5.7.1. But 5.6.x is not mentioned anywhere. Does it mean 5.6.x is not affected? Surely, no. I hope it does NOT mean any attempt by Oracle to pretend that 5.6 is bugs free. Looks like Sveta had just forgotten to check or report result on this version when following her great bugs verification procedure.

I would say that the above was just a one time mistake, but then look at Bug #68145 that was verified by Sveta in less than 30 minutes after my last comment there (and "verification", at the level I can do it as community member busy with main job actually). It was verified on many versions again, 5.0.97, 5.1.69, 5.5.31, 5.7.1, but NOT on 5.6.x. This looks like a trend now, and I do not like it. There are bugs in 5.6.9, 5.6.10 and even 5.6.11, there is nothing bad about this if they are noted, processed and fixed fast. There is not (good) reason to skip checking on mentioning this version. I am monitoring carefully anyway, so nothing in public database will pass unnoticed and unknown to MySQL community.

Serious bug in InnoDB was reported (and verified on both 5.5.27, 5.6.9-rc and recent 5.6 code) this week, Bug #68148. After executing SET FOREIGN_KEY_CHECKS=0; you can easily drop index unsed by foreign key and then the tables becomes unusable (you can not even drop it with SQL statement) after server restart. As it is not a recent regression, I am not sure it would be easy to fix, so better just avoid DDL with the setting above.

When 5.6 is approaching GA it is really strange to see bugs in new/key features of MySQL 5.6 with unclear status. Check Bug #66916 (replication). We can only guess is it fixed in 5.6.10 or not. Check Bug #66865 (performance regression in 5.6 that is all about performance) reported by my colleague Vadim more than 4 months ago. It is still just "Open". So, is there a regression or not? Or it is just forgotten?

When bugs are forgotten and test cases are not added to the regression test suite (now we, in Community, can not check if they are added), we are doomed to see the same problems again and again. If you are Oracle customer, ask them what Bug #68178 is about (in a support request probably), what versions are affected and had it been previously reported and fixed. If you care what is it about (Oracle will probably just tell you to upgrade to the version with the fix eventually), it is about an easy way to crash MySQL server by sending many smart SELECT convert_tz(...) in a row. I hope 5.6 will NOT be released as GA before this bug is fixed.

Forgotten bug reports had always been a problem, but I tried to at least review all "Open" bug reports once in while. Now we can still see bug reports with clear, repeatable test case finally got from reporter (like Bug #67517), or bug that is just easy to verify by code review (like Bug #67386) open and having no visible attention for months. Some bugs just hang in other intermediate states for ages as well (after verification), like Bug #56267. Some are verified, but they look serious and still remain just in "Verified" status, like Bug #67638 (optimizer).

Chances are high for a casual reporter to never report again when he gets no reply for months. This bad trend continues, but with less bugs open reports there is chance to overcome this trend eventually.

Hardly any of new key features of 5.6 is bug free. For example, PERFORMANCE_SCHEMA, as it was recently found out (see Bug #68180) does not cover all execution paths. Comparing to bugs listed at the beginning of this post it may be not that serious, but I am a bit tired of getting new features in GA that are NOT implemented completely (as it happened to 5.0, 5.1 and 5.5 GA).

The last (but not the least) potential problem with 5.6 is related to the documentation. There are missing details and misleading statements there (see Bug #68097), sections like that are no longer relevand after recent funny bug fixes (see funny fix to Bug #63435 about innodb_version server variable) and misprints in release notes (like Bug #68181). Some sections are still work in progress it seems, like Some fixes (like Bug #67759) are not documented it seems. Maybe manual being not yet ready is the reason why MySQL 5.6 had not been declared GA yet?

Now about good trends. This week I've noted more MySQL engineers working on bugs processing. Long waiting Bug #68023 was finally verified by Matt Lord, who rarely worked on bugs not related to customer issues in the past. Look at his detailed research in Bug #67517 that I've noted (and "escalated") just today. Erlend Dahl had noted and verified awful Bug #68127 soon after my "escalation" and it was closed in 2 days (with the fix in 5.6.10, one of the reasons I though that it will be GA and announced really soon during the week)! Way to go, Oracle, really!

As a result, this week Oracle finally managed to decrease number of "Open" bug reports to the level smaller than during my last day in the company, August 31, 2012. Since December 2012 number of open bug reports is decreased by more than 170! New bug reports are processed fast, see Bug #68144 as one of recent examples. Verified in less that 3 hours (as well as two other bugs from Hartmut reported that day). Looks like it is not a problem now for Oracle to keep up with inflow of at least server bug reports (I'll write about Cluster and Workbench bugs in details in some of the following issues).

Another (IMHO good) trend - Oracle customers, at least those who did that before, do not hesitate to report bugs in public database (as I've suggested to do last year). See Bug #68165 as one of recent examples related to 5.6 and upgrade to it.

Finally, some fun. Make sure you check the oldest and still not closed MySQL bugs, Bug #2. 10 years passed and the problem is still far from solved! This is awful, really.

MariaDB also contributed some fun for us all with their version 10.0. Read Bug #68187 and then try to guess if Oracle is going to fix it any time soon. More fun in the next issue, I hope...


  1. I like how the changelog entry for says "the server would exit" instead of "the server would crash". Crashing isn't really "exiting".

    1. The fact that it was fixed fast and will not be in 5.6 GA (I hope) matters more than exact text in the release notes or closing comment.

    2. About, I think you missed that entry, documented in the bug report:

      [22 Jan 16:00] Paul Dubois

      Noted in 5.6.10 (not 5.6.11) changelog.

      -- Marc Alff

  2. > Looks like Sveta had just forgotten to check or report result on this version when following her great bugs verification procedure.

    Yeah, I forgot to add 5.6 tree to my auto-test script after trunk became 5.7. Other Oracle engineers reminded me about it already after I published that blog post.

    1. OK, so this was just a mistake in your testing scripts/setup :) Now, please, check that bugs I've mentioned on 5.6, to remove any reasons for my claims in the post about "trend"...