perf: stream the slow query log during import to fix the 10GB memory footprint

[TheWitness]

Summary

Addresses the import memory blow-up (problem #1): a ~1.6GB slow query log (~1M queries) pushed the importer past 10GB RSS.

Root cause

import_logfile() read the entire log into a PHP array up front with file($logfile). For a multi-gigabyte log that costs many times the file's own size in PHP array/string overhead — hence >10GB for a 1.6GB log.

Fix

Stream the log a line at a time with fgets() instead. This is a clean fit because the detail rows are already flushed to plugin_slowlog_details in SLOWLOG_IMPORT_BATCH_SIZE (1000-row) batches as parsing proceeds — so once the whole-file slurp is removed, nothing accumulates in memory and RSS stays flat regardless of log size. (This is the "insert as you go" item.)

• file($logfile) → fopen() + while (($l = fgets($fh)) !== false), with fclose() after the loop.
• No change to parsing, batching, or the generated SQL.

Validation

• php -l clean.
• tests/Integration/ImportLogfileParsingTest.php drives import_logfile() against a real temp-file log and asserts the generated INSERT SQL; streaming produces byte-identical output, so it stays green.
• CHANGELOG updated under the unreleased 2.6 section; no version bump (per request).

Not in this PR (proposed follow-up)

Your other points — de-normalizing plugin_slowlog_details_methods from methodid to a method varchar (and dropping the plugin_slowlog_methods/plugin_slowlog_tables dictionary-table usage), and restructuring the SELECT DISTINCT sld.* details query — are a larger schema + query change that rewrites ~6 Pest tests under the 100%-patch-coverage gate and needs a clean install to drop the old tables. I kept this PR to the memory fix (the most severe, blocking issue) so it lands cleanly; happy to do the de-normalization as a focused follow-up PR next.

[Copilot]

Copilot review overview

🟡 Changes recommended

Stream read errors can silently produce partial imports marked as successful.

Review effort: Balanced
Findings: 1

Open (1)

• Distinguish fgets read errors from EOF before finalizing import · New

What changed in this PR

Streams slow-query logs during import to avoid whole-file memory usage.

Changes:

• Replaces file() with fopen()/fgets() streaming.
• Documents the performance improvement.

File	Description
includes/​slowlog_functions.php	Streams log parsing line by line.
CHANGELOG.md	Records the memory optimization.

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