postgres connector: replace pgxpool.Pool with pgx.Conn (#1163)

Pools make sense when shared across application (eg, CatalogPool)
It doesn't make sense creating a pool per connector,
& it turns out with a bit of modification we can get by with connections

This comes with some restrictions:
Connections require exclusion
So when using a goroutine, a 2nd connection may be necessary
(this was transparently handled by pool before)
Similarly, rows must be closed before executing another query

flow/activities/slot.go

@@ -2,75 +2,19 @@ package activities
 
 import (
 	"context"
-	"fmt"
-	"log/slog"
 	"time"
 
 	"github.com/PeerDB-io/peer-flow/connectors"
-	"github.com/PeerDB-io/peer-flow/connectors/utils/monitoring"
-	"github.com/PeerDB-io/peer-flow/dynamicconf"
-	"github.com/PeerDB-io/peer-flow/peerdbenv"
 )
 
-func (a *FlowableActivity) handleSlotInfo(
-	ctx context.Context,
-	srcConn connectors.CDCPullConnector,
-	slotName string,
-	peerName string,
-) error {
-	slotInfo, err := srcConn.GetSlotInfo(slotName)
-	if err != nil {
-		slog.WarnContext(ctx, "warning: failed to get slot info", slog.Any("error", err))
-		return err
-	}
-
-	if len(slotInfo) == 0 {
-		slog.WarnContext(ctx, "warning: unable to get slot info", slog.Any("slotName", slotName))
-		return nil
-	}
-
-	deploymentUIDPrefix := ""
-	if peerdbenv.PeerDBDeploymentUID() != "" {
-		deploymentUIDPrefix = fmt.Sprintf("[%s] ", peerdbenv.PeerDBDeploymentUID())
-	}
-
-	slotLagInMBThreshold := dynamicconf.PeerDBSlotLagMBAlertThreshold(ctx)
-	if (slotLagInMBThreshold > 0) && (slotInfo[0].LagInMb >= float32(slotLagInMBThreshold)) {
-		a.Alerter.AlertIf(ctx, fmt.Sprintf("%s-slot-lag-threshold-exceeded", peerName),
-			fmt.Sprintf(`%sSlot `+"`%s`"+` on peer `+"`%s`"+` has exceeded threshold size of %dMB, currently at %.2fMB!
-cc: <!channel>`,
-				deploymentUIDPrefix, slotName, peerName, slotLagInMBThreshold, slotInfo[0].LagInMb))
-	}
-
-	// Also handles alerts for PeerDB user connections exceeding a given limit here
-	maxOpenConnectionsThreshold := dynamicconf.PeerDBOpenConnectionsAlertThreshold(ctx)
-	res, err := srcConn.GetOpenConnectionsForUser()
-	if err != nil {
-		slog.WarnContext(ctx, "warning: failed to get current open connections", slog.Any("error", err))
-		return err
-	}
-	if (maxOpenConnectionsThreshold > 0) && (res.CurrentOpenConnections >= int64(maxOpenConnectionsThreshold)) {
-		a.Alerter.AlertIf(ctx, fmt.Sprintf("%s-max-open-connections-threshold-exceeded", peerName),
-			fmt.Sprintf(`%sOpen connections from PeerDB user `+"`%s`"+` on peer `+"`%s`"+
-				` has exceeded threshold size of %d connections, currently at %d connections!
-cc: <!channel>`,
-				deploymentUIDPrefix, res.UserName, peerName, maxOpenConnectionsThreshold, res.CurrentOpenConnections))
-	}
-
-	if len(slotInfo) != 0 {
-		return monitoring.AppendSlotSizeInfo(ctx, a.CatalogPool, peerName, slotInfo[0])
-	}
-	return nil
-}
-
 func (a *FlowableActivity) recordSlotSizePeriodically(
 	ctx context.Context,
 	srcConn connectors.CDCPullConnector,
 	slotName string,
 	peerName string,
 ) {
 	// ensures slot info is logged at least once per SyncFlow
-	err := a.handleSlotInfo(ctx, srcConn, slotName, peerName)
+	err := srcConn.HandleSlotInfo(ctx, a.Alerter, a.CatalogPool, slotName, peerName)
 	if err != nil {
 		return
 	}
@@ -81,7 +25,7 @@ func (a *FlowableActivity) recordSlotSizePeriodically(
 	for {
 		select {
 		case <-ticker.C:
-			err := a.handleSlotInfo(ctx, srcConn, slotName, peerName)
+			err := srcConn.HandleSlotInfo(ctx, a.Alerter, a.CatalogPool, slotName, peerName)
 			if err != nil {
 				return
 			}

flow/connectors/core.go

@@ -17,6 +17,7 @@ import (
 	connsqlserver "github.com/PeerDB-io/peer-flow/connectors/sqlserver"
 	"github.com/PeerDB-io/peer-flow/generated/protos"
 	"github.com/PeerDB-io/peer-flow/model"
+	"github.com/PeerDB-io/peer-flow/shared/alerting"
 )
 
 var ErrUnsupportedFunctionality = errors.New("requested connector does not support functionality")
@@ -45,12 +46,13 @@ type CDCPullConnector interface {
 	// PullFlowCleanup drops both the Postgres publication and replication slot, as a part of DROP MIRROR
 	PullFlowCleanup(jobName string) error
 
+	// HandleSlotInfo update monitoring info on slot size etc
+	// threadsafe
+	HandleSlotInfo(ctx context.Context, alerter *alerting.Alerter, catalogPool *pgxpool.Pool, slotName string, peerName string) error
+
 	// GetSlotInfo returns the WAL (or equivalent) info of a slot for the connector.
 	GetSlotInfo(slotName string) ([]*protos.SlotInfo, error)
 
-	// GetOpenConnectionsForUser returns the number of open connections for the user configured in the peer.
-	GetOpenConnectionsForUser() (*protos.GetOpenConnectionsForUserResult, error)
-
 	// AddTablesToPublication adds additional tables added to a mirror to the publication also
 	AddTablesToPublication(req *protos.AddTablesToPublicationInput) error
 }

flow/connectors/postgres/cdc.go

@@ -139,7 +139,6 @@ func (p *PostgresCDCSource) PullRecords(req *model.PullRecordsRequest) error {
 	}
 
 	pgConn := p.replConn.PgConn()
-	p.logger.Info("created replication connection")
 
 	// start replication
 	var clientXLogPos, startLSN pglogrepl.LSN