feat(collector): add sys per-user latency/type collectors; harden user_summary; docs + compose integration test

[sklochkov]

What & why

This PR adds two opt-in collectors that expose per-user statement activity from MySQL’s sys schema, and fixes a failure mode in the existing --collect.sys.user_summary on MySQL 8.x. It also includes unit tests, docs, and a Docker Compose harness to exercise collectors locally.

New collectors (opt-in)

• --collect.sys.user_summary_by_statement_latency
  Scrapes sys.x$user_summary_by_statement_latency to expose per-user totals and latency aggregates.

• --collect.sys.user_summary_by_statement_type
  Scrapes sys.x$user_summary_by_statement_type to expose per-user by statement type aggregates.

Requirements: MySQL ≥ 5.7 with performance_schema enabled and the sys schema available.

Harden existing collector

• --collect.sys.user_summary
  Some MySQL 8.x installations occasionally surface negative values for current_memory / total_memory_allocated in the sys view, which previously caused a scan into uint64 to fail and the scrape to error. We now clamp these to ≥ 0 (via SQL), avoiding exporter errors while preserving metric semantics.

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Flags & metrics

--collect.sys.user_summary_by_statement_latency

Labels: user
Emits:

• mysql_sys_user_summary_by_statement_latency_total
• mysql_sys_user_summary_by_statement_latency (seconds total)
• mysql_sys_user_summary_by_statement_max_latency (seconds)
• mysql_sys_user_summary_by_statement_lock_latency (seconds total)
• mysql_sys_user_summary_by_statement_cpu_latency (seconds total)
• mysql_sys_user_summary_by_statement_rows_sent_total
• mysql_sys_user_summary_by_statement_rows_examined_total
• mysql_sys_user_summary_by_statement_rows_affected_total
• mysql_sys_user_summary_by_statement_full_scans_total

--collect.sys.user_summary_by_statement_type

Labels: user, statement
Emits:

• mysql_sys_user_summary_by_statement_type_total
• mysql_sys_user_summary_by_statement_type_latency (seconds total)
• mysql_sys_user_summary_by_statement_type_max_latency (seconds)
• mysql_sys_user_summary_by_statement_type_lock_latency (seconds total)
• mysql_sys_user_summary_by_statement_type_cpu_latency (seconds total)
• mysql_sys_user_summary_by_statement_type_rows_sent_total
• mysql_sys_user_summary_by_statement_type_rows_examined_total
• mysql_sys_user_summary_by_statement_type_rows_affected_total
• mysql_sys_user_summary_by_statement_type_full_scans_total

Implementation notes

• Metric names follow the existing sys_user_summary.go style (namespace mysql, subsystem sys, metric stem user_summary_by_*).
• Latencies are converted from picoseconds → seconds using the shared picoSeconds constant.
• Exported as gauges, in line with other sys collectors.

Behavior change in --collect.sys.user_summary

• Query uses GREATEST(current_memory, 0) and GREATEST(total_memory_allocated, 0) to avoid negative values in 8.x. No metric name/type changes.

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Testing

Unit tests

• New: sys_user_summary_by_statement_latency_test.go
• New: sys_user_summary_by_statement_type_test.go
• Updated: sys_user_summary_test.go (robust SQL matcher, guard channel reads, fix column name, align with clamping)

Each test uses sqlmock and the repo’s MetricResult/readMetric helpers to verify:

• SQL is issued against the correct sys.x$… view,
• label sets and value order,
• latency ps→seconds conversion,
• metric types (gauges).

Run:

go test ./collector -run UserSummary go test ./...

Docker Compose integration harness (developer convenience)

A self-contained script to validate collectors against a local MySQL:

• docker-compose.yml (fixed network mysql-test)

• mysql/conf.d/perf-schema.cnf (ensures Performance Schema/consumers on)

• mysql/initdb/01-users.sql (creates/grants exporter and app; caching_sha2_password)

• seed/seed.sh (simple INSERT/SELECT/UPDATE/SLEEP to populate sys views)

• test_compose_collectors.sh

  • builds local exporter image
  • ensures users/grants if the data dir is reused
  • starts exporter per --collect.* flag (inside the Docker network; no host port binding)
  • fetches /metrics from inside the network
  • writes per-flag logs to _testlogs/
  • includes a broad TESTS set (plus optional auto-discovery of flags from --help)

Run:

./test_compose_collectors.sh

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Backwards compatibility & perf

• New collectors are disabled by default; no changes for existing users unless flags are set.
• The user_summary clamp only affects rare negative values; otherwise behavior and types are unchanged.
• Queries are single simple SELECTs over sys.x$… views; expected to be inexpensive with Performance Schema enabled.

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How to review

Key files:

• collector/sys_user_summary_by_statement_latency.go
• collector/sys_user_summary_by_statement_type.go
• collector/sys_user_summary.go (clamp)
• collector/*_test.go (new + updated tests)
• README.md (docs for new flags + integration test)
• docker-compose.yml, mysql/, seed/, test_compose_collectors.sh (integration harness)

Happy to split the test harness/docs into a separate PR if you prefer, but they’re isolated from runtime code.