Re: backup manifests

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.
>

Review comments on 0004:

1.
I don't think we need o_manifest_with_checksums variable,
manifest_with_checksums can be used instead.

2.
We need to document this new option for pg_basebackup and basebackup.

3.
Also, instead of keeping manifest_with_checksums as a global variable, we
should pass that to the required function. Patch 0002 already modified the
signature of all relevant functions anyways. So just need to add one more
bool
variable there.

4.
Why we need a "File" at the start of each entry as we are adding files only?
I wonder if we also need to provide a tablespace name and directory marker
so
that we have "Tablespace" and "Dir" at the start.

5.
If I don't provide manifest-with-checksums option then too I see that
checksum
is calculated for backup_manifest file itself. Is that intentional or
missed?
I think we should omit that too if this option is not provided.

6.
Is it possible to get only a backup manifest from the server? A client like
pg_basebackup can then use that to fetch files reading that.

Thanks

>
>
>
> 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
>

--
Jeevan Chalke
Associate Database Architect & Team Lead, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company