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,
On Mon, Sep 30, 2019 at 5:31 AM Jeevan Chalke
<jeevan.chalke@enterprisedb.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