Evaluate using Profile-Guided Optimization (PGO) and Post-Link Optimization (PLO)

[zamazan4ik]

Hi!

Recently I checked many optimizations like PGO and PLO (mostly with LLVM BOLT) improvements on multiple projects including many databases - the results are available here. According to the tests, these optimizations can help to achieve better performance in many cases. I think trying to optimize Iggy's performance with PGO and PLO can be an interesting idea.

I can suggest the following action points:

• Perform PGO on the database in more scenarios. If it shows improvements - add a note to the documentation about possible improvements in the project performance with PGO.
• Providing an easier way (e.g. a build option) to build scripts with PGO can be helpful for the end-users and maintainers since they will be able to optimize iggy-server according to their workloads.
• Testing Post-Link Optimization techniques (like LLVM BOLT) would be interesting too (Clang and Rustc already use BOLT as an addition to PGO) but I recommend starting from the usual PGO.

Here are some examples of how PGO optimization is integrated into other projects:

• Rustc: a CI script for the multi-stage build
• GCC:
  • Official docs, section "Building with profile feedback"
• Clang: Docs
• Python:
  • CPython: README
  • Pyston: README
• Go: Bash script
• V8: Bazel flag
• ChakraCore: Scripts
• Chromium: Script
• Firefox: Docs
  • Thunderbird has PGO support too
• PHP - Makefile command and old Centminmod scripts
• MySQL: CMake script
• YugabyteDB: GitHub commit
• FoundationDB: Script
• Zstd: Makefile
• Pydantic-core: GitHub PR
• file.d: GitHub PR
• OceanBase: CMake flag

Unfortunately, for now, building the project with LTO and PGO enabled at the same time fails due to a bug in the compiler: rust-lang/rust#115344 (comment) . I suggest waiting for the fix in the upstream since disabling LTO is a worse option (IMHO).

I would be happy to answer your questions about all the optimizations above.

[hubcio]

Hello, I tested PGO with BOLT like 6 months ago, we got ~15% performance improvement. We have this issue:
#200

I have branch somewhere with kind-of basic flow (build with pgo, run performance tests, build again, build with bolt, etc.)

For now, we simply don't have enough time to pursuit this :) I know this is really nice low hanging fruit and we will probably do it in future.

[zamazan4ik]

Wow, such a nice improvement - it's great. I hope one day you will find enough time for PGO integration into the main iggy-rs development branch.

[hubcio]

Also, thank you! I will ping you if I'll have more questions - did you already join our discord?

[zamazan4ik]

I didn't know about it before - just joined. Thanks!