lazily connect to PostGIS

emissions/aep/srgspec_osm.go

@@ -23,6 +23,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"sync"
 
 	backoff "github.com/cenkalti/backoff/v4"
 	"github.com/ctessum/geom"
@@ -57,6 +58,8 @@ type SrgSpecOSM struct {
 	// in MergeNames.
 	MergeMultipliers []float64 `json:"merge_multipliers"`
 
+	connectPostGISOnce sync.Once
+	postGISURL string
 	conn *pgxpool.Pool
 }
 
@@ -74,39 +77,43 @@ type SrgSpecOSM struct {
 // and the PostGIS database should have the "hstore" extension installed before
 // loading the data.
 func ReadSrgSpecOSM(ctx context.Context, r io.Reader, postGISURL string) (*SrgSpecs, error) {
-	if postGISURL == "" {
-		return nil, fmt.Errorf("PostGIS URL is required")
-	}
-	// Connect to database.
-	var conn *pgxpool.Pool
-	var err error
-	err = backoff.Retry(func() error {
-		conn, err = pgxpool.Connect(ctx, postGISURL)
-		if err != nil {
-			return err
-		}
-		return nil
-	}, backoff.WithMaxRetries(backoff.NewExponentialBackOff(), 10))
-	if err != nil {
-		return nil, fmt.Errorf("Unable to connect to PostGIS database %s after 10 tries: %w\n", postGISURL, err)
-	}
-
 	// Read the surrogate specification.
 	d := json.NewDecoder(r)
 	var o []*SrgSpecOSM
-	if err = d.Decode(&o); err != nil {
+	if err := d.Decode(&o); err != nil {
 		return nil, err
 	}
 
 	// Add the db connection to each surrogate.
 	srgs := NewSrgSpecs()
 	for _, s := range o {
-		s.conn = conn
+		s.postGISURL = postGISURL
 		srgs.Add(s)
 	}
 	return srgs, nil
 }
 
+func (s *SrgSpecOSM) connectPostGIS() {
+	if s.postGISURL == "" {
+		panic(fmt.Errorf("PostGIS URL is required"))
+	}
+
+	// Connect to database.
+	var conn *pgxpool.Pool
+	var err error
+	err = backoff.Retry(func() error {
+		conn, err = pgxpool.Connect(context.Background(), s.postGISURL)
+		if err != nil {
+			return err
+		}
+		return nil
+	}, backoff.WithMaxRetries(backoff.NewExponentialBackOff(), 10))
+	if err != nil {
+		panic(fmt.Errorf("unable to connect to PostGIS database %s after 10 tries: %w", s.postGISURL, err))
+	}
+	s.conn = conn
+}
+
 func (srg *SrgSpecOSM) backupSurrogateNames() []string { return srg.BackupSurrogateNames }
 func (srg *SrgSpecOSM) region() Country                { return srg.Region }
 func (srg *SrgSpecOSM) code() string                   { return srg.Code }
@@ -164,6 +171,8 @@ func (srg *SrgSpecOSM) getSrgData(gridData *GridDef, inputLoc *Location, tol flo
 	}
 	tagKeys = tagKeys[:len(tagKeys)-1] // Remove trailing comma.
 
+	srg.connectPostGISOnce.Do(srg.connectPostGIS)
+
 	rows, err := srg.conn.Query(ctx, `
 	SELECT 
 		hstore_to_array(tags) tags, ST_AsBinary(way)