From 0db7008aac09661a9444dffd94a2e1b10dca7576 Mon Sep 17 00:00:00 2001
From: Bel LaPointe <153096461+breel-render@users.noreply.github.com>
Date: Tue, 9 Dec 2025 16:49:46 -0700
Subject: [PATCH] pg-queue-demo

---
 cmd/{pg-queue => pg-queue-demo}/README.md |   0
 cmd/pg-queue-demo/main.go                 | 164 ++++++++++++++++++++++
 cmd/pg-queue/main.go                      |  31 ----
 3 files changed, 164 insertions(+), 31 deletions(-)
 rename cmd/{pg-queue => pg-queue-demo}/README.md (100%)
 create mode 100644 cmd/pg-queue-demo/main.go
 delete mode 100644 cmd/pg-queue/main.go

diff --git a/cmd/pg-queue/README.md b/cmd/pg-queue-demo/README.md
similarity index 100%
rename from cmd/pg-queue/README.md
rename to cmd/pg-queue-demo/README.md
diff --git a/cmd/pg-queue-demo/main.go b/cmd/pg-queue-demo/main.go
new file mode 100644
index 0000000..4d4286c
--- /dev/null
+++ b/cmd/pg-queue-demo/main.go
@@ -0,0 +1,164 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"sync/atomic"
+	"time"
+
+	"pg/src/with"
+
+	_ "github.com/lib/pq"
+)
+
+func main() {
+	if err := with.Context(run); err != nil {
+		panic(err)
+	}
+}
+
+func run(ctx context.Context) error {
+	fs := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
+	c := fs.String("c", "postgresql://pulsegres:pulsegres@localhost:15432", "conn string")
+	if err := fs.Parse(os.Args[1:]); err != nil {
+		panic(err)
+	}
+
+	return with.PSQL(ctx, *c, func(pg *sql.DB) error {
+		log.Println("creating tables...")
+		if _, err := pg.ExecContext(ctx, `
+			CREATE SCHEMA IF NOT EXISTS "queue";
+
+			CREATE TABLE IF NOT EXISTS "queue"."queue" (
+				id UUID NOT NULL DEFAULT GEN_RANDOM_UUID() PRIMARY KEY,
+				payload BYTEA NOT NULL,
+				created_at TIMESTAMP NOT NULL DEFAULT NOW(),
+				attempts INTEGER DEFAULT 0,
+				reservation UUID,
+				checked_out_at TIMESTAMP
+			);
+
+			CREATE TABLE IF NOT EXISTS "queue"."archive" (
+				id UUID NOT NULL PRIMARY KEY,
+				payload BYTEA NOT NULL,
+				created_at TIMESTAMP NOT NULL,
+				archived_at TIMESTAMP NOT NULL DEFAULT NOW()
+			);
+		`); err != nil {
+			return err
+		}
+
+		enqueue := func(a any) error {
+			b, _ := json.Marshal(a)
+			_, err := pg.ExecContext(ctx, `INSERT INTO "queue"."queue" (payload) VALUES ($1)`, b)
+			return err
+		}
+
+		mustCheckout := func() (string, []byte, error) {
+			rows, err := pg.QueryContext(ctx, `
+				UPDATE "queue"."queue"
+				SET
+					reservation = GEN_RANDOM_UUID(),
+					attempts = attempts+1,
+					checked_out_at = NOW()
+				WHERE
+					id IN (
+						SELECT id
+						FROM "queue"."queue"
+						WHERE
+							attempts < 100
+							AND (reservation IS NULL OR NOW() - checked_out_at > INTERVAL '1 minute')
+						FOR UPDATE SKIP LOCKED
+						LIMIT 1
+					)
+				RETURNING reservation, payload
+			`)
+			if err != nil {
+				return "", nil, err
+			}
+
+			var reservation string
+			var payload []byte
+			for rows.Next() {
+				if err := rows.Scan(&reservation, &payload); err != nil {
+					return "", nil, fmt.Errorf("failed to scan reservation,payload: %w", err)
+				}
+			}
+
+			return reservation, payload, rows.Err()
+		}
+
+		resolve := func(reservation string) error {
+			_, err := pg.ExecContext(ctx, `
+				WITH deleted AS (
+					DELETE FROM "queue"."queue"
+					WHERE
+						reservation=$1
+						AND NOW() - checked_out_at < INTERVAL '1 minute'
+					RETURNING id, payload, created_at
+				)
+				INSERT INTO "queue"."archive" (
+					id, payload, created_at
+				) SELECT * FROM deleted
+			`, reservation)
+			return err
+		}
+
+		start := time.Now()
+		var enqueues atomic.Uint64
+		var dequeues atomic.Uint64
+		go with.Every(ctx, 2*time.Second, func() {
+			seconds := uint64(time.Since(start).Seconds())
+			if seconds < 1 {
+				seconds = 1
+			}
+			e := enqueues.Load()
+			d := dequeues.Load()
+			log.Printf("%d enqueues (%d per second), %d dequeues (%d per second) over %d seconds",
+				e,
+				e/seconds,
+				d,
+				d/seconds,
+				seconds,
+			)
+		})
+
+		go with.Every(ctx, 1, func() {
+			if err := enqueue(1); err != nil {
+				log.Printf("failed to enqueue: %v", err)
+			} else {
+				enqueues.Add(1)
+			}
+		})
+
+		with.Every(ctx, 1, func() {
+			reservation, payload, err := mustCheckout()
+			if err != nil {
+				log.Println("failed checkout:", err)
+				return
+			}
+
+			if reservation == "" {
+				return
+			}
+
+			if string(payload) != "1" {
+				log.Printf("bad checkout: unexpected payload %q", payload)
+				return
+			}
+
+			if err := resolve(reservation); err != nil {
+				log.Printf("failed to resolve: %v", err)
+				return
+			}
+
+			dequeues.Add(1)
+		})
+		return ctx.Err()
+	})
+}
diff --git a/cmd/pg-queue/main.go b/cmd/pg-queue/main.go
deleted file mode 100644
index 40f1794..0000000
--- a/cmd/pg-queue/main.go
+++ /dev/null
@@ -1,31 +0,0 @@
-package main
-
-import (
-	"context"
-	"database/sql"
-	"flag"
-	"os"
-
-	"pg/src/with"
-
-	_ "github.com/lib/pq"
-)
-
-func main() {
-	if err := with.Context(run); err != nil {
-		panic(err)
-	}
-}
-
-func run(ctx context.Context) error {
-	fs := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
-	c := fs.String("c", "postgresql://pulsegres:pulsegres@localhost:15432", "conn string")
-	if err := fs.Parse(os.Args[1:]); err != nil {
-		panic(err)
-	}
-
-	return with.PSQL(ctx, *c, func(pg *sql.DB) error {
-		<-ctx.Done()
-		return nil
-	})
-}