Fix sys.user_summary scraper to handle negative current_memory values

[maleki-it]

Summary

Fixes the sys.user_summary scraper failing when the current_memory column contains negative values in MySQL 8.0 Enterprise.

Problem

The scraper attempts to parse current_memory as uint64 (unsigned integer), which fails when MySQL returns negative values. According to MySQL documentation, negative memory values can occur when:

• Memory is freed faster than it is allocated
• Threads terminate and release memory asynchronously

This causes the scraper to fail with the following error:

sql: Scan error on column index 9, name "current_memory": 
converting driver.Value type []uint8 ("-16360") to a uint64: invalid syntax

Solution

• Changed current_memory variable type from uint64 to int64 in collector/sys_user_summary.go
• This allows the scraper to handle both positive and negative values
• Values are still converted to float64 for Prometheus metrics (no breaking changes)
• Added test case in collector/sys_user_summary_test.go with negative value (-16360) to prevent regression

Changes

• File: collector/sys_user_summary.go (Line 121)

  • Changed: current_memory uint64 → current_memory int64

• File: collector/sys_user_summary_test.go (Lines 80-92)

  • Added: Test case with current_memory = "-16360"

Testing

• ✅ All existing tests pass
• ✅ New test case covers negative memory values
• ✅ Verified on MySQL 8.0.35 Enterprise with --collect.sys.user_summary flag
• ✅ Confirmed metrics export correctly with both positive and negative values
• ✅ No breaking changes - backward compatible with existing deployments

Environment Tested

• MySQL Version: 8.0.35 Enterprise
• Exporter Version: 0.18.0
• Platform: linux/amd64
• Flags Used: --collect.sys.user_summary, --log.level=debug

Impact

• Breaking Changes: None
• Backward Compatibility: 100% - positive values work exactly as before
• Performance Impact: None - both uint64 and int64 are 64-bit types
• Security Impact: None - read-only operation

Related

This issue affects users running MySQL 8.0 Enterprise with the sys.user_summary collector enabled.

[maleki-it]

Related to #982