Re: 9.4 btree index corruption

On Sun, May 25, 2014 at 7:16 AM, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com
> wrote:

> On 05/21/2014 10:22 PM, Jeff Janes wrote:
>
>> Testing partial-write crash-recovery in 9.4 (e12d7320ca494fd05134847e30)
>> with foreign keys, I found some btree index corruption.
>>
>> ...

>
>> https://drive.google.com/folderview?id=0Bzqrh1SO9FcENWd6ZXlwVWpxU0E&
>> usp=sharing
>>
>
> I downloaded the data directory and investigated. I got this message when
> I started it up:
>
> 20392 2014-05-25 05:51:37.835 PDT:ERROR: right sibling 4044 of block 460
> is not next child 23513 of block 86458 in index "foo_p_id_idx"
> 20392 2014-05-25 05:51:37.835 PDT:CONTEXT: automatic vacuum of table
> "jjanes.public.foo"
>
> Interestingly, it's complaining about parent page 86458, while yours
> claimed it was 1264. I don't know why; perhaps a huge number of insertions
> happened after that error, causing the parent level pages to be split,
> moving the downlinks it complains about to the right. Did you continue
> running the test after that error occurred?
>

Yes, I didn't set it up to abort upon vacuum errors, so it continued to run
until it reached the 1,000,000 wrap around limit.

Between when the vacuums started failing and when it reached wrap around
limit, it seemed to run normally (other than the increasing bloat and
non-advancement of frozenxid).

I only noticed the ERROR when I was looking through the log file in
postmortem. Looking back, I see 10 errors with 1264, then it switched to
86458. I didn't notice the change and reported only the first ERROR
message.

I'll apply your patch and see what happens, but 90 further hours of testing
gave no more occurrences of the error so I'm afraid that not seeing errors
is not much evidence that the error was fixed. So I'll have to rely on
your knowledge of the code.

> This is what the tree looks like around those pages:
>
> Level 1:
> +-------------+ +-------------+ +-------------+
> | Blk 1264 | | Blk 160180 | | Blk 86458 |
> | | | | | |
> | Downlinks: | <-> | Downlinks: | <-> | Downlinks: |
> | ... | | ... | | 1269 |
> | | | | | 460 |
> | | | | | 23513 |
> +-------------+ +-------------+ +-------------+
>
>

Is this done with the pageinspect extension?

With the attached patch, I was able to get past that error, but when VACUUM
> reaches the end, I got this:
>
> jjanes=# vacuum foo;
> ERROR: database is not accepting commands to avoid wraparound data loss
> in database "jjanes"
> HINT: Stop the postmaster and vacuum that database in single-user mode.
> You might also need to commit or roll back old prepared transactions.
>
> That seems like an unrelated issue, I'll start a new thread about that.
>

Yeah, that's expected. Since vacuum failures don't abort the test, it ran
on until something else stopped it.

> Many thanks for the testing, Jeff!

You're welcome. If only I was as good at fixing things as at breaking
them.

Cheers,

Jeff