Heavily diven by Claude code. To be cut down and refactored in following
commits.

Aligns with the postgres package on how we handle non-valid server
address.

Removes the New constructor; which we can reintroduce if and when we
need to set up automatic client construction from Fairway / known
config locations

Initial registration and collection of pool metrics. Will require
refactoring to more cleanly register these metrics along with attaching the
hook required for the command metrics.

All metrics now use prometheus.BuildFQName with configurable Namespace
(default "gitlab") and Subsystem (default "redis"), producing names like
gitlab_redis_command_duration_seconds. A "name" constant label is added to
all metrics to identify the client instance.

Replaces registerOrReuse with registerCollector, which errors on duplicate
descriptors rather than silently reusing an existing collector. The previous
approach dropped pool stats and merged command metrics across distinct clients.

Merges newMetricsHook and registerPoolMetrics into a single newMetrics entry
point.

Unexports StatGetter and NewPoolCollector as internal implementation details.

- Updates metric name strings (redis_command_* → gitlab_redis_command_*)
- Splits TestMetrics_MultipleClientsSharedRegisterer into two tests:
  - TestMetrics_DistinctNamesSharedRegisterer — distinct names share a registerer without error
  - TestMetrics_DuplicateNameSharedRegistererErrors — same name returns an error with the expected message

Adds 14 fields covering the connection, timeout, pool, and retry parameters
that teams commonly need to tune. ClientName is auto-set to cfg.Name so every
client is identifiable in CLIENT LIST output without additional configuration.

Adds a Logger *slog.Logger field to Config. When set, a loggingHook is
registered that emits a structured log entry for every command and
pipeline: redis_command, redis_key, redis_duration_ms, and error_message on
failures.

redis.Nil is not treated as an error. Pipeline executions are logged as a single
entry with redis_command="pipeline" and redis_pipeline_size.

Errors trigger Warn level; normal completions use Debug. Start and
Shutdown log at Info.

The client name is baked into a child logger via .With() at construction
time so all entries carry it automatically without repeating it at each
call site.

When Logger is nil, the logging hook is not registered (no per-command
overhead). A discard logger is stored on the client so Start and
Shutdown can log unconditionally without nil guards.

This avoids logging `redis_key=""` for pipelines and other commands which
do not have a redis_key.

db.system    -> db.system.name
db.statement -> db.operation.name

From: https://opentelemetry.io/docs/specs/semconv/db/redis/

From https://opentelemetry.io/docs/specs/semconv/db/redis/:

> For transactions and pipelined calls, if the individual operations are known
  to have the same command then that command SHOULD be used prepended by MULTI
  or PIPELINE . Otherwise db.operation.name SHOULD be MULTI or PIPELINE.

From https://opentelemetry.io/docs/specs/semconv/db/redis/:

> db.operation.batch.size: Operations are only considered batches when they
  contain two or more operations, and so db.operation.batch.size SHOULD never
  be 1.

This commit splits the logic for setting up and registering the pool
metrics into their own file. This better shows that the pool metrics are
pull metrics which do not depend on the metrics_hook, which is entirely
responsible for the per-command metrics.

Small corrections to documentation and comments

Duo Developer authored May 22, 2026 and Alessio Caiazza committed May 22, 2026

Resolved conflict in v2/go.sum:
- Kept fairway v1.18.0 hashes (from master, matching go.mod)
- Kept gopher-lua v1.1.1 hashes (indirect dep still in go.mod)
- Dropped zeebo/xxh3 v1.1.0 (no longer referenced in go.mod)

Run go mod tidy

feat(v2/redis): add instrumented Redis client

See merge request !497

Merged-by: Elliot Forbes <eforbes@gitlab.com>
Approved-by: Alessio Caiazza <code.git@caiazza.info>
Approved-by: Elliot Forbes <eforbes@gitlab.com>
Co-authored-by: Duo Developer <service_account_group_9970_1976e9ecde3c53c783b64edb9ae993eb@noreply.gitlab.com>
Co-authored-by: Luke Hollinda <lhollinda@gitlab.com>