Thank you Jeevan for reviewing the patch.
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.
Yes, done in the latest version of opatch.
2.
We need to document this new option for pg_basebackup and basebackup.
Done, attaching documentation patch with the mail.
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.
yes, earlier I did that implementation but later found that we already
have checksum related global variable i.e. noverify_checksums, so
that it will be clean implementation - rather modifying the function definition
to pass the variable (which is actually global for the operation).
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.
Sorry, I am not quite sure about this, may be Robert is right person
to answer this.
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.
Oops yeah, corrected this in the latest version of patch.
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.
Currently we don't have any option to just get the manifest file from the
server. I am not sure but why we need this at this point of time.
