server: Change zlib compression level

[dveeden]

This was flate.HuffmanOnly (-2) to 6 to match what MySQL does.

Note that compress/flate doesn't define a const for level 6.

What problem does this PR solve?

Issue Number: close #47278

Problem Summary:

Related: #36780

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

The compression level for zlib level was updated to match the compression level of MySQL

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[dveeden]

With this patch:

diff --git a/server/internal/packetio.go b/server/internal/packetio.go
index e015c0ce08..2ffbf5ed7f 100644
--- a/server/internal/packetio.go
+++ b/server/internal/packetio.go
@@ -381,12 +381,13 @@ func (cw *compressedWriter) Flush() error {
        // https://dev.mysql.com/doc/dev/mysql-server/latest/page_protocol_basic_compression_packet.html
        // suggests a MIN_COMPRESS_LENGTH of 50.
        minCompressLength := 50
+       zlibCompressDefaultLevel := 6
        data := cw.buf.Bytes()
        cw.buf.Reset()
 
        switch cw.compressionAlgorithm {
        case mysql.CompressionZlib:
-               w, err = zlib.NewWriterLevel(&payload, zlib.HuffmanOnly)
+               w, err = zlib.NewWriterLevel(&payload, zlibCompressDefaultLevel)
        case mysql.CompressionZstd:
                w, err = zstd.NewWriter(&payload, zstd.WithEncoderLevel(cw.zstdLevel))
        default:

Patched (165 bytes compressed, 2065 uncompressed):

Original (411 bytes compressed, 2065 uncompressed):

[tiprow]

Hi @dveeden. Thanks for your PR.

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[dveeden]

/ok-to-test

[dveeden]

/test all

[codecov]

Codecov Report

Merging #47387 (9b4f551) into master (95378e5) will increase coverage by 0.3942%.
The diff coverage is 100.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #47387        +/-   ##
================================================
+ Coverage   72.3183%   72.7125%   +0.3942%     
================================================
  Files          1352       1373        +21     
  Lines        400846     407184      +6338     
================================================
+ Hits         289885     296074      +6189     
- Misses        91782      92333       +551     
+ Partials      19179      18777       -402     

Flag	Coverage Δ
integration	38.5068% <0.0000%> (?)
unit	72.3193% <100.0000%> (+0.0010%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9913% <ø> (ø)
parser	84.7544% <ø> (ø)
br	48.7512% <ø> (-4.3470%)	⬇️

[dveeden]

/test all

[dveeden]

/retest

[lance6716]

Can you check the result of 16M SQL as the issue described?

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, lance6716

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-10-03 14:31:44.771488195 +0000 UTC m=+544302.358598324: ☑️ agreed by lance6716.
• 2023-10-03 17:18:19.401414729 +0000 UTC m=+554296.988524859: ☑️ agreed by hawkingrei.

[hawkingrei]

/retest

[jackysp]

Why "6" here?

[lance6716]

This is MySQL's choice #47278 (comment)