Update docs regarding lost connections while updating jobs (#39)

backends/postgres/postgres_backend.go

@@ -504,13 +504,20 @@ func (p *PgBackend) moveToDeadQueue(ctx context.Context, tx pgx.Tx, j *jobs.Job,
 }
 
 // updateJob updates the status of jobs with: status, run time, error messages, and retries
+//
 // if the retry count exceeds the maximum number of retries for the job, move the job to the dead jobs queue
 //
-// if `tx`'s underlying connection dies, it results in this function throwing an error and job status inaccurately
-// reflecting the status of the job and its number of retries.
-// TODO: Handle dropped connections when updating job status in PgBackend
-// e.g. acquiring a new connection in the event of connection failure
-// nolint: cyclop
+// if `tx`'s underlying connection dies while updating job status, the transaction will fail, and the job's original
+// status will be reflecting in the database.
+//
+// The implication of this is that:
+// - the job's 'error' field will not reflect any errors the occurred in the handler
+// - the job's retry count is not incremented
+// - the job's run time will remain its original value
+// - the job has its original 'status'
+//
+// ultimately, this means that any time a database connection is lost while updating job status, then the job will be
+// processed at least one more time.
 func (p *PgBackend) updateJob(ctx context.Context, jobErr error) (err error) {
 	status := internal.JobStatusProcessed
 	errMsg := ""
@@ -566,13 +573,19 @@ func (p *PgBackend) updateJob(ctx context.Context, jobErr error) (err error) {
 func (p *PgBackend) start(ctx context.Context, queue string) (err error) {
 	var h handler.Handler
 	var ok bool
+
 	if h, ok = p.handlers[queue]; !ok {
 		return fmt.Errorf("%w: %s", handler.ErrNoHandlerForQueue, queue)
 	}
 
-	listenJobChan := p.listen(ctx, queue)        // listen for 'new' jobs
+	listenJobChan, ready := p.listen(ctx, queue) // listen for 'new' jobs
+	defer close(ready)
+
 	pendingJobsChan := p.pendingJobs(ctx, queue) // process overdue jobs *at startup*
 
+	// wait for the listener to connect and be ready to listen
+	<-ready
+
 	// process all future jobs and retries
 	go func() { p.scheduleFutureJobs(ctx, queue) }()
 
@@ -782,8 +795,9 @@ func (p *PgBackend) handleJob(ctx context.Context, jobID int64, h handler.Handle
 
 	err = tx.Commit(ctx)
 	if err != nil {
-		p.logger.Error("unable to commit job transaction. retrying this job may dupliate work", err, "job_id", job.ID)
-		return fmt.Errorf("unable to commit job transaction. retrying this job may dupliate work: %w", err)
+		errMsg := "unable to commit job transaction. retrying this job may dupliate work:"
+		p.logger.Error(errMsg, err, "job_id", job.ID)
+		return fmt.Errorf("%s %w", errMsg, err)
 	}
 
 	return nil
@@ -793,59 +807,56 @@ func (p *PgBackend) handleJob(ctx context.Context, jobID int64, h handler.Handle
 // TODO: There is currently no handling of listener disconnects in PgBackend.
 // This will lead to jobs not getting processed until the worker is restarted.
 // Implement disconnect handling.
-func (p *PgBackend) listen(ctx context.Context, queue string) (c chan int64) {
+func (p *PgBackend) listen(ctx context.Context, queue string) (c chan int64, ready chan bool) {
 	c = make(chan int64)
+	ready = make(chan bool)
 
 	go func(ctx context.Context) {
+		conn, err := p.pool.Acquire(ctx)
+		if err != nil {
+			p.logger.Error("unable to acquire new listener connnection", err)
+			return
+		}
+		defer p.release(ctx, conn, queue)
+
+		// set this connection's idle in transaction timeout to infinite so it is not intermittently disconnected
+		_, err = conn.Exec(ctx, fmt.Sprintf("SET idle_in_transaction_session_timeout = '0'; LISTEN %s", queue))
+		if err != nil {
+			err = fmt.Errorf("unable to configure listener connection: %w", err)
+			p.logger.Error("unable to configure listener connection", err)
+			return
+		}
+
+		// notify start() that we're ready to listen for jobs
+		ready <- true
+
 		for {
-			conn, err := p.pool.Acquire(ctx)
-			if err != nil {
-				p.logger.Error("unable to acquire new connnection", err)
-				return
-			}
-
-			// set this connection's idle in transaction timeout to infinite so it is not intermittently disconnected
-			_, err = conn.Exec(ctx, fmt.Sprintf("SET idle_in_transaction_session_timeout = '0'; LISTEN %s", queue))
-			if err != nil {
-				err = fmt.Errorf("unable to configure listener connection: %w", err)
-				p.logger.Error("unable to configure listener connection", err)
-				time.Sleep(time.Second) // don't hammer the db
-				p.release(ctx, conn, queue)
-				continue
-			}
-
 			notification, waitErr := conn.Conn().WaitForNotification(ctx)
 			if waitErr != nil {
 				if errors.Is(waitErr, context.Canceled) {
-					p.release(ctx, conn, queue)
 					return
 				}
 
 				p.logger.Error("failed to wait for notification", waitErr)
-				p.release(ctx, conn, queue)
 				continue
 			}
 
 			var jobID int64
 			if jobID, err = strconv.ParseInt(notification.Payload, 0, 64); err != nil {
 				p.logger.Error("unable to fetch job", err)
-				p.release(ctx, conn, queue)
 				continue
 			}
 
 			// check if Shutdown() has been called
 			if jobID == shutdownJobID {
-				p.release(ctx, conn, queue)
 				return
 			}
 
 			c <- jobID
-
-			p.release(ctx, conn, queue)
 		}
 	}(ctx)
 
-	return c
+	return c, ready
 }
 
 func (p *PgBackend) release(ctx context.Context, conn *pgxpool.Conn, queue string) {

backends/postgres/postgres_backend_test.go

@@ -3,6 +3,7 @@ package postgres_test
 import (
 	"context"
 	"errors"
+	"fmt"
 	"os"
 	"testing"
 	"time"
@@ -11,6 +12,7 @@ import (
 	"github.com/acaloiaro/neoq/backends/postgres"
 	"github.com/acaloiaro/neoq/config"
 	"github.com/acaloiaro/neoq/handler"
+	"github.com/acaloiaro/neoq/internal"
 	"github.com/acaloiaro/neoq/jobs"
 )
 
@@ -75,7 +77,6 @@ func TestBasicJobMultipleQueue(t *testing.T) {
 	const queue2 = "testing2"
 	done := make(chan bool)
 	doneCnt := 0
-	defer close(done)
 
 	var timeoutTimer = time.After(5 * time.Second)
 
@@ -115,7 +116,7 @@ func TestBasicJobMultipleQueue(t *testing.T) {
 	jid, e := nq.Enqueue(ctx, &jobs.Job{
 		Queue: queue,
 		Payload: map[string]interface{}{
-			"message": "hello world",
+			"message": fmt.Sprintf("hello world: %d", internal.RandInt(10000000000)),
 		},
 	})
 	if e != nil || jid == jobs.DuplicateJobID {
@@ -125,7 +126,7 @@ func TestBasicJobMultipleQueue(t *testing.T) {
 	jid2, e := nq.Enqueue(ctx, &jobs.Job{
 		Queue: queue2,
 		Payload: map[string]interface{}{
-			"message": "hello world",
+			"message": fmt.Sprintf("hello world: %d", internal.RandInt(10000000000)),
 		},
 	})
 	if e != nil || jid2 == jobs.DuplicateJobID {
@@ -146,7 +147,6 @@ results_loop:
 		}
 	}
 
-	time.Sleep(time.Second)
 	if err != nil {
 		t.Error(err)
 	}