Connection Error Tracking & Auto-Reconnect

[fcostaoliveira]

This PR introduces connection error tracking and a configurable auto-reconnect mechanism to memtier_benchmark. The goal is to make benchmarks more resilient when running against clusters where TLS errors, timeouts, or dropped connections can otherwise abort runs prematurely.

Connection Error Tracking

• Tracks and reports total connection errors per client group
• Adds connection error metrics in both text and JSON outputs (Connection Errors and Connection Errors/sec)
• Connection errors are displayed in live progress reports only when errors occur (backwards compatible):

  [RUN #1 45%, 900 secs] 45 threads 200 conns 12 conn errors: 1000000 ops...
  

New CLI Options for Reconnection

• --reconnect-on-error → Enable automatic reconnection when connection errors occur (default: disabled)
• --max-reconnect-attempts=N → Limit reconnection retries (default: 0, unlimited)
• --reconnect-backoff-factor=F → Exponential backoff multiplier for retry delays (default: 0, no backoff)
• --connection-timeout=SECS → Timeout in seconds before considering a connection attempt failed (default: 0, disabled)

Client Behavior

• On BEV_EVENT_ERROR, BEV_EVENT_EOF, or connection timeout → update error stats, attempt reconnection (if enabled)
• Supports exponential backoff for retries with configurable backoff factor
• Backoff delay resets on successful connection
• Reconnection attempts are logged to stderr for visibility
• If max attempts exceeded or reconnect disabled, the client terminates gracefully

Backwards Compatibility

All new features are opt-in and fully backwards compatible:

• Default behavior unchanged: Reconnection is disabled by default (--reconnect-on-error must be explicitly enabled)
• Configuration defaults: All new options default to 0 (disabled/unlimited)
• Output format: Connection errors only appear in progress display when errors actually occur
• Existing workflows: No impact on existing scripts, benchmarks, or automation

[kamran-redis]

Any reason --reconnect-on-error should not be enabled by default other than backward compatibility?

[fcostaoliveira]

Any reason --reconnect-on-error should not be enabled by default other than backward compatibility?

@kamran-redis like you mentioned just to be backwards compatible. all added features on this PR have the default behaviour that's backwards compatible