Re: Fixing or Mitigating this ERROR: invalid page in block 35217 of relation base/16421/3192429

Hi Chris,

On Wed, Nov 29, 2023 at 7:38 PM Chris Travers <chris(dot)travers(at)gmail(dot)com>
wrote:

>
>
> On Wed, Nov 29, 2023 at 4:36 PM Abdul Qoyyuum <aqoyyuum(at)cardaccess(dot)com(dot)bn>
> wrote:
>
>> Hi all,
>>
>> Knowing that it's a data corruption issue, the only way to fix this is to
>> vacuum and reindex the database. What was suggested was the following:
>>
>> SET zero_damaged_pages = 0; # This is so that we can have the application
>> to continue to run
>> VACUUM FULL VERBOSE ANALYSE; # Do a full vacuum and analyse the problem
>> if possible.
>> REINDEX DATABASE "core"; # Then do a reindex and clean it up.
>>
>
> So first, to clear up some confusion on my part here:
>
> This procedure doesn't make a lot of sense to me. But did it clear up the
> issue?
>
Yeah it did fix the issue before (same issue as last year) and it has fixed
the problem that just happened a few days ago (almost exactly a year ago).

>
> In any of these cases, it is extremely important to diagnose the system
> properly. If you have a fault in your storage device or RAID controller,
> for example, you are asking for more corruption and data loss later.
>

> At first I thought maybe you mistyped something and then realized there
> were a few issues with the process so it actually didn't make sense.
>
> First, zero_damaged_pages defaults to 0, and I can think of no reason to
> set it explicitly.
> Secondly, a vacuum full has to reindex, so there is no reason to do a
> reindex following. Your whole procedure is limited to a vacuum full, when
> a reindex is the only part that could affect this. If it did work,
> reindexing is the only part that would have been helpful.
>
Oh that makes sense actually. Thanks.

>
> On to the question of what to do next....
>
>>
>> We're on Postgresql 12. This has worked before it happened (almost
>> exactly a year ago) and I think this needs a more permanent solution. I've
>> looked at routine vacuuming and checked the autovacuum is set to on and the
>> following configurations:
>>
>> core=> select name, setting from pg_settings where name like
>> 'autovacuum%';
>> name | setting
>> -------------------------------------+-----------
>> autovacuum | on
>> autovacuum_analyze_scale_factor | 0.1
>> autovacuum_analyze_threshold | 50
>> autovacuum_freeze_max_age | 200000000
>> autovacuum_max_workers | 3
>> autovacuum_multixact_freeze_max_age | 400000000
>> autovacuum_naptime | 60
>> autovacuum_vacuum_cost_delay | 2
>> autovacuum_vacuum_cost_limit | -1
>> autovacuum_vacuum_scale_factor | 0.2
>> autovacuum_vacuum_threshold | 50
>> autovacuum_work_mem | -1
>> (12 rows)
>>
>> Can anyone advise if there's anything else we can do? We have no clue
>> what causes the invalid page block and we are running a High Availability
>> cluster set up but we are hoping that there may be a way to mitigate it.
>>
>>
> You need to figure out why the corruption is happening. This is most
> likely, in my experience, not a PostgreSQL bug, but usually something that
> happens on the hardware layer or an environmental factor. It could be
> failin storage or CPU. Or it could be something like bad electrical input
> or insufficient cooling (I have seen index and even table corruption issues
> from both of these).
>
> If this is a server you run, the first things I would check are:
> 1. Is there a good-quality UPS that the server is plugged into? Are the
> batteries in good working order?
>
The servers are dual powered and hooked up to both supplied electricity,
with a backup generator and if that fails, it will switch over to the UPS.
All of these are supplied and maintained by the data centre that the
servers are at. There have been no electrical problems so far.

> 2. Is the server somewhere that may be sitting in a pocket of hot air?
>
As you can imagine, the data centre has air-conditioning and floored fans
blowing hot air up and out, keeping all servers cooled. Checking on the
blade servers that the database VM sits on shows that the temperature is
optimally sitting at 65 degrees celsius. So I don't think it's a
temperature problem either.

>
> Once you have ruled these out, the next things to check are CPU, memory,
> and storage health. Unfortunately checking these is harder but you can
> check SMART indications, and other diagnostic indicators.
>
Would this top stats be useful? The database does get busy especially at
peak hours.

top - 10:04:25 up 782 days, 43 min, 2 users, load average: 1.20, 1.14,
1.10
Tasks: 415 total, 3 running, 412 sleeping, 0 stopped, 0 zombie
Cpu(s): 22.7%us, 13.8%sy, 0.0%ni, 63.2%id, 0.2%wa, 0.0%hi, 0.1%si,
0.1%st
Mem: 8160156k total, 7832828k used, 327328k free, 34584k buffers
Swap: 1048572k total, 304396k used, 744176k free, 6674428k cached

We are running on a SAN group disk storage. I guess I should take a closer
look at the disks. Thanks for the pointer.

>
> However, once these errors start happening, you are in danger territory
> and need to find out why (and correct the underlying problem) before you
> get data loss.
>
Thanks for the warning. We'll see what we can find.

>
> --
> Best Wishes,
> Chris Travers
>
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