Re: backup manifests

Hi,

Since now we are generating the backup manifest file with each backup, it
provides us an option to validate the given backup.
Let's say, we have taken a backup and after a few days, we want to check
whether that backup is validated or corruption-free without restarting the
server.

Please find attached POC patch for same which will be based on the latest
backup manifest patch from Rushabh. With this functionality, we add new
option to pg_basebackup, something like --verify-backup.
So, the syntax would be:
./bin/pg_basebackup --verify-backup -D <backup_directory_path>

Basically, we read the backup_manifest file line by line from the given
directory path and build the hash table, then scan the directory and
compare each file with the hash entry.

Thoughts/suggestions?

On Tue, Nov 19, 2019 at 3:30 PM Rushabh Lathia <rushabh(dot)lathia(at)gmail(dot)com>
wrote:

>
>
> My colleague Suraj did testing and noticed the performance impact
> with the checksums. On further testing, he found that specifically with
> sha its more of performance impact.
>
> Please find below statistics:
>
> no of tables without checksum SHA256
> checksum % performnce
> overhead
> with
> SHA-256 md5 checksum % performnce
> overhead with md5 CRC checksum % performnce
> overhead with
> CRC
> 10 (100 MB
> in each table) real 0m10.957s
> user 0m0.367s
> sys 0m2.275s real 0m16.816s
> user 0m0.210s
> sys 0m2.067s 53% real 0m11.895s
> user 0m0.174s
> sys 0m1.725s 8% real 0m11.136s
> user 0m0.365s
> sys 0m2.298s 2%
> 20 (100 MB
> in each table) real 0m20.610s
> user 0m0.484s
> sys 0m3.198s real 0m31.745s
> user 0m0.569s
> sys 0m4.089s
> 54% real 0m22.717s
> user 0m0.638s
> sys 0m4.026s 10% real 0m21.075s
> user 0m0.538s
> sys 0m3.417s 2%
> 50 (100 MB
> in each table) real 0m49.143s
> user 0m1.646s
> sys 0m8.499s real 1m13.683s
> user 0m1.305s
> sys 0m10.541s 50% real 0m51.856s
> user 0m0.932s
> sys 0m7.702s 6% real 0m49.689s
> user 0m1.028s
> sys 0m6.921s 1%
> 100 (100 MB
> in each table) real 1m34.308s
> user 0m2.265s
> sys 0m14.717s real 2m22.403s
> user 0m2.613s
> sys 0m20.776s 51% real 1m41.524s
> user 0m2.158s
> sys 0m15.949s
> 8% real 1m35.045s
> user 0m2.061s
> sys 0m16.308s 1%
> 100 (1 GB
> in each table) real 17m18.336s
> user 0m20.222s
> sys 3m12.960s real 24m45.942s
> user 0m26.911s
> sys 3m33.501s 43% real 17m41.670s
> user 0m26.506s
> sys 3m18.402s 2% real 17m22.296s
> user 0m26.811s
> sys 3m56.653s
>
> sometimes, this test
> completes within the
> same time as without
> checksum. approx. 0.5%
>
>
> Considering the above results, I modified the earlier Robert's patch and
> added
> "manifest_with_checksums" option to pg_basebackup. With a new patch.
> by default, checksums will be disabled and will be only enabled when
> "manifest_with_checksums" option is provided. Also re-based all patch set.
>
>
>
> Regards,
>
> --
> Rushabh Lathia
> www.EnterpriseDB.com
>
> On Tue, Oct 1, 2019 at 5:43 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
>> On Mon, Sep 30, 2019 at 5:31 AM Jeevan Chalke
>> <jeevan(dot)chalke(at)enterprisedb(dot)com> wrote:
>> > Entry for directory is not added in manifest. So it might be difficult
>> > at client to get to know about the directories. Will it be good to add
>> > an entry for each directory too? May be like:
>> > Dir <dirname> <mtime>
>>
>> Well, what kind of corruption would this allow us to detect that we
>> can't detect as things stand? I think the only case is an empty
>> directory. If it's not empty, we'd have some entries for the files in
>> that directory, and those files won't be able to exist unless the
>> directory does. But, how would we end up backing up an empty
>> directory, anyway?
>>
>> I don't really *mind* adding directories into the manifest, but I'm
>> not sure how much it helps.
>>
>> --
>> Robert Haas
>> EnterpriseDB: http://www.enterprisedb.com
>> The Enterprise PostgreSQL Company
>>
>>
>>
>
> --
> Rushabh Lathia
>

--
--

Thanks & Regards,
Suraj kharage,
EnterpriseDB Corporation,
The Postgres Database Company.