Bug 2188504

Summary:	The "hammer export" command using single thread encryption causes a performance bottleneck.
Product:	Red Hat Satellite	Reporter:	Brenden Wood <bwood>
Component:	Pulp	Assignee:	satellite6-bugs <satellite6-bugs>
Status:	ON_QA ---	QA Contact:	Shweta Singh <shwsingh>
Severity:	medium	Docs Contact:
Priority:	high
Version:	Unspecified	CC:	ahumbe, dalley, dkliban, ggainey, pcreech, rchan, rlavi, shwsingh
Target Milestone:	6.14.0	Keywords:	Performance, Triaged
Target Release:	Unused
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	pulpcore-3.18.20-1, pulpcore-3.21.10-1, pulpcore-3.23.8-1, pulpcore-3.22.12-1	Doc Type:	If docs needed, set a value
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Last Closed:		Type:	Bug
Regression:	---	Mount Type:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Brenden Wood 2023-04-21 00:26:01 UTC

Description of problem:

We identified a severe bottleneck in the way hammer exports work and found the code in upstream Pulp.

Line 406 of https://github.com/pulp/pulpcore/blob/main/pulpcore/app/tasks/export.py

"with tarfile.open(tarfile_fp, "w|gz", fileobj=split_process.stdin)"

The tarfile Python module creates tar files using the gizp Python module.

Data compression for the gzip Python module is provided by the zlib Python module.

The zlib Python module calls the zlib library.

If defaults are used the whole way through this series of events, the result is a single threaded pulp process doing compression of a tarball containing a massive content library. This bottleneck and can make large hammer exports take several days.

Modifying the lines that tell the tarfile.open function to NOT use compression ( change "w|gz" to "w" ) dramatically speeds up the hammer export. In our testing it reduced the time from days to just hours. The drawback is the file size was significantly larger, but the trade-off is worthwhile given we have tight timeframes and plentiful disk capacity.

Can this bottleneck be addressed with multi-threaded gzip compression?

and/or

Can a hammer command line option for no compression be implemented?

Version-Release number of selected component (if applicable): 6.10 onwards ( Pulp 3 )

How reproducible:
Run a hammer export and monitor Pulp processes. One process with run at 100% CPU. Modify the abovementioned Python script to NOT use gzip encryption, and an uncompressed tarball will be created instead much quicker and with multiple Pulp processes.

Steps to Reproduce:
1. Run a "hammer export". Monitor the Pulp process CPU usage and time taken to complete export.
2. Change the abovementioned Python code in Pulp.
3. Run a "hammer export" again and note performance improvement.

Actual results:
A single threaded pulp process doing compression of a tarball and being bottlenecked.

Expected results:
Multi-threaded gzip compression that can take full advantage of the CPU and IO of the Satellite server and not be severly bottlenecked.

Additional info:

IO wait is very low when using single threaded compression, indicating that CPU single thread is the issue. When not using encryption (removing the bottleneck) iowait increases.

This issue is causing significant delays for a couple of customers. Corresponding support tickets will be submitted soon.

Comment 1 Daniel Alley 2023-05-25 14:25:50 UTC

The default compression level of tarfile with gzip compression is level 9, the highest and most computationally intensive level.  Possibly compression would be more viable at a lower level - based on various benchmarks level 3 ought to be about 4x faster than level 9 but with a compression level only 15-20% worse.

Comment 2 Daniel Alley 2023-05-25 14:54:28 UTC

Brendan, don't forget to attach the customer cases.

If you have a reproducer (or a customer willing to experiment), what is the impact of adding "compresslevel=1" to that line?  e.g.

"with tarfile.open(tarfile_fp, "w|gz", compresslevel=1, fileobj=split_process.stdin)"

Comment 3 Daniel Alley 2023-05-25 14:59:25 UTC

(don't forget to restart the services, of course).

Also, how large is the uncompressed export in question, in gigabytes?

Comment 4 Brenden Wood 2023-05-30 04:20:27 UTC

Hi Daniel,

We have the ability to test this with a customer so I will try this out and report back. From memory, we were dealing with an export over a terabyte in size, but I will have to confirm that. 

Thanks

Comment 5 Daniel Alley 2023-05-30 04:33:17 UTC

Brendan, I thought I had posted this but apparently not - that patch actually will not work, because it requires code present in Python 3.12 only.  Please don't ask the customer to try it just yet.

Comment 6 Robin Chan 2023-06-13 12:05:49 UTC

The Pulp upstream bug status is at closed. Updating the external tracker on this bug.

Comment 8 Daniel Alley 2023-07-27 14:34:46 UTC

Anyone tracking this may also be interested in https://bugzilla.redhat.com/show_bug.cgi?id=2226950