pkg/database: Limit the number of open connections to 1 (#39)

Getting a `database is locked` error. This [upstream
issue](mattn/go-sqlite3#274 (comment))
suggested limiting the number of connection to one and it seems to have
helped. It's not idea, but I need to move on.

ref #38

pkg/database/sqlite.go

@@ -101,6 +101,11 @@ func Open(logger log15.Logger, dbpath string) (*DB, error) {
 		return nil, fmt.Errorf("error opening the SQLite3 database at %q: %w", dbpath, err)
 	}
 
+	// Getting an error `database is locked` when data is being inserted in the
+	// database at a fast rate. This will slow down read/write from the database
+	// but at least none of them will fail due to connection issues.
+	sdb.SetMaxOpenConns(1)
+
 	db := &DB{DB: sdb, logger: logger.New("dbpath", dbpath)}
 
 	return db, db.createTables()

pkg/database/sqlite_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sync"
 	"testing"
 	"time"
 
@@ -254,6 +255,66 @@ func TestInsertNarInfoRecord(t *testing.T) {
 			t.Errorf("want %q got %q", want, got)
 		}
 	})
+
+	t.Run("can write many narinfos", func(t *testing.T) {
+		var wg sync.WaitGroup
+
+		errC := make(chan error)
+
+		for i := 0; i < 10000; i++ {
+			wg.Add(1)
+
+			go func() {
+				defer wg.Done()
+
+				hash, err := helper.RandString(128, nil)
+				if err != nil {
+					errC <- fmt.Errorf("expected no error but got: %w", err)
+
+					return
+				}
+
+				tx, err := db.Begin()
+				if err != nil {
+					errC <- fmt.Errorf("expected no error but got: %w", err)
+
+					return
+				}
+
+				//nolint:errcheck
+				defer tx.Rollback()
+
+				if _, err := db.InsertNarInfoRecord(tx, hash); err != nil {
+					errC <- fmt.Errorf("expected no error got: %w", err)
+
+					return
+				}
+
+				if err := tx.Commit(); err != nil {
+					errC <- fmt.Errorf("expected no error got: %w", err)
+
+					return
+				}
+			}()
+		}
+
+		done := make(chan struct{})
+
+		go func() {
+			wg.Wait()
+
+			close(done)
+		}()
+
+		for {
+			select {
+			case err := <-errC:
+				t.Errorf("got an error: %s", err)
+			case <-done:
+				return
+			}
+		}
+	})
 }
 
 //nolint:paralleltest