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| 1 | +// SPDX-License-Identifier: AGPL-3.0-or-later |
| 2 | + |
| 3 | +package db |
| 4 | + |
| 5 | +import ( |
| 6 | + "context" |
| 7 | + "sync/atomic" |
| 8 | + |
| 9 | + "github.com/jackc/pgx/v5" |
| 10 | +) |
| 11 | + |
| 12 | +// QueryCounter is a pgx QueryTracer that increments a per-context |
| 13 | +// counter on every Query/QueryRow/Exec. The counter lives on the |
| 14 | +// request context, so the tracer is safe to install at pool-config |
| 15 | +// time even when most requests don't care. |
| 16 | +// |
| 17 | +// Use case: handler integration tests assert "this route does ≤ N |
| 18 | +// DB queries." The tracer + WithCounter / FromContext + a tiny |
| 19 | +// middleware (web/middleware/query_count_assert.go) make that |
| 20 | +// assertion a one-liner. |
| 21 | +// |
| 22 | +// Production runs leave the tracer installed but never call |
| 23 | +// WithCounter; the per-conn overhead is one atomic-load per query |
| 24 | +// (the tracer reads the context value but the counter is nil so |
| 25 | +// no Add fires). |
| 26 | +type QueryCounter struct{} |
| 27 | + |
| 28 | +type queryCounterKey struct{} |
| 29 | + |
| 30 | +// counter is the per-context Adder. Atomic so concurrent Query |
| 31 | +// invocations on the same request context (rare but possible — |
| 32 | +// goroutines per row) don't undercount. |
| 33 | +type counter struct { |
| 34 | + n atomic.Int64 |
| 35 | +} |
| 36 | + |
| 37 | +// WithCounter returns a derived context that records query counts. |
| 38 | +// Pair with Read. |
| 39 | +func WithCounter(ctx context.Context) context.Context { |
| 40 | + return context.WithValue(ctx, queryCounterKey{}, &counter{}) |
| 41 | +} |
| 42 | + |
| 43 | +// FromContext reports how many tracer events have fired against ctx. |
| 44 | +// Returns 0 when WithCounter wasn't called on this context. |
| 45 | +func FromContext(ctx context.Context) int64 { |
| 46 | + c, ok := ctx.Value(queryCounterKey{}).(*counter) |
| 47 | + if !ok { |
| 48 | + return 0 |
| 49 | + } |
| 50 | + return c.n.Load() |
| 51 | +} |
| 52 | + |
| 53 | +// TraceQueryStart implements pgx.QueryTracer. The counter increments |
| 54 | +// at start, not end, so a slow query still counts. |
| 55 | +func (QueryCounter) TraceQueryStart(ctx context.Context, _ *pgx.Conn, _ pgx.TraceQueryStartData) context.Context { |
| 56 | + if c, ok := ctx.Value(queryCounterKey{}).(*counter); ok { |
| 57 | + c.n.Add(1) |
| 58 | + } |
| 59 | + return ctx |
| 60 | +} |
| 61 | + |
| 62 | +// TraceQueryEnd implements pgx.QueryTracer. No-op; the start tick is |
| 63 | +// the meaningful event. |
| 64 | +func (QueryCounter) TraceQueryEnd(context.Context, *pgx.Conn, pgx.TraceQueryEndData) {} |
