| 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) {} |
| 65 |