fix(db): add additional connection pool for projection spooling (#7094)

* fix(db): add additional connection pool for projection spooling

* use correct connection pool for projections

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/database/dialect/connections.go

@@ -1,43 +1,90 @@
 package dialect
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+)
 
-type ConnectionInfo struct {
-	EventstorePusher ConnectionConfig
-	ZITADEL          ConnectionConfig
-}
+var (
+	ErrNegativeRatio       = errors.New("ratio cannot be negative")
+	ErrHighSumRatio        = errors.New("sum of pusher and projection ratios must be < 1")
+	ErrIllegalMaxOpenConns = errors.New("MaxOpenConns of the database must be higher than 3 or 0 for unlimited")
+	ErrIllegalMaxIdleConns = errors.New("MaxIdleConns of the database must be higher than 3 or 0 for unlimited")
+	ErrInvalidPurpose      = errors.New("DBPurpose out of range")
+)
 
+// ConnectionConfig defines the Max Open and Idle connections for a DB connection pool.
 type ConnectionConfig struct {
 	MaxOpenConns,
 	MaxIdleConns uint32
 }
 
-func NewConnectionInfo(openConns, idleConns uint32, pusherRatio float64) (*ConnectionInfo, error) {
-	if pusherRatio < 0 || pusherRatio > 1 {
-		return nil, errors.New("EventPushConnRatio must be between 0 and 1")
-	}
-	if openConns != 0 && openConns < 2 {
-		return nil, errors.New("MaxOpenConns of the database must be higher that 1")
+// takeRatio of MaxOpenConns and MaxIdleConns from config and returns
+// a new ConnectionConfig with the resulting values.
+func (c *ConnectionConfig) takeRatio(ratio float64) (*ConnectionConfig, error) {
+	if ratio < 0 {
+		return nil, ErrNegativeRatio
 	}
 
-	info := new(ConnectionInfo)
-
-	info.EventstorePusher.MaxOpenConns = uint32(pusherRatio * float64(openConns))
-	info.EventstorePusher.MaxIdleConns = uint32(pusherRatio * float64(idleConns))
-
-	if openConns != 0 && info.EventstorePusher.MaxOpenConns < 1 && pusherRatio > 0 {
-		info.EventstorePusher.MaxOpenConns = 1
+	out := &ConnectionConfig{
+		MaxOpenConns: uint32(ratio * float64(c.MaxOpenConns)),
+		MaxIdleConns: uint32(ratio * float64(c.MaxIdleConns)),
 	}
-	if idleConns != 0 && info.EventstorePusher.MaxIdleConns < 1 && pusherRatio > 0 {
-		info.EventstorePusher.MaxIdleConns = 1
+	if c.MaxOpenConns != 0 && out.MaxOpenConns < 1 && ratio > 0 {
+		out.MaxOpenConns = 1
+	}
+	if c.MaxIdleConns != 0 && out.MaxIdleConns < 1 && ratio > 0 {
+		out.MaxIdleConns = 1
 	}
 
-	if openConns != 0 {
-		info.ZITADEL.MaxOpenConns = openConns - info.EventstorePusher.MaxOpenConns
-	}
-	if idleConns != 0 {
-		info.ZITADEL.MaxIdleConns = idleConns - info.EventstorePusher.MaxIdleConns
-	}
-
-	return info, nil
+	return out, nil
+}
+
+// NewConnectionConfig calculates [ConnectionConfig] values from the passed ratios
+// and returns the config applicable for the requested purpose.
+//
+// openConns and idleConns must be at least 3 or 0, which means no limit.
+// The pusherRatio and spoolerRatio must be between 0 and 1.
+func NewConnectionConfig(openConns, idleConns uint32, pusherRatio, projectionRatio float64, purpose DBPurpose) (*ConnectionConfig, error) {
+	if openConns != 0 && openConns < 3 {
+		return nil, ErrIllegalMaxOpenConns
+	}
+	if idleConns != 0 && idleConns < 3 {
+		return nil, ErrIllegalMaxIdleConns
+	}
+	if pusherRatio+projectionRatio >= 1 {
+		return nil, ErrHighSumRatio
+	}
+
+	queryConfig := &ConnectionConfig{
+		MaxOpenConns: openConns,
+		MaxIdleConns: idleConns,
+	}
+	pusherConfig, err := queryConfig.takeRatio(pusherRatio)
+	if err != nil {
+		return nil, fmt.Errorf("event pusher: %w", err)
+	}
+	spoolerConfig, err := queryConfig.takeRatio(projectionRatio)
+	if err != nil {
+		return nil, fmt.Errorf("projection spooler: %w", err)
+	}
+
+	// subtract the claimed amount
+	if queryConfig.MaxOpenConns > 0 {
+		queryConfig.MaxOpenConns -= pusherConfig.MaxOpenConns + spoolerConfig.MaxOpenConns
+	}
+	if queryConfig.MaxIdleConns > 0 {
+		queryConfig.MaxIdleConns -= pusherConfig.MaxIdleConns + spoolerConfig.MaxIdleConns
+	}
+
+	switch purpose {
+	case DBPurposeQuery:
+		return queryConfig, nil
+	case DBPurposeEventPusher:
+		return pusherConfig, nil
+	case DBPurposeProjectionSpooler:
+		return spoolerConfig, nil
+	default:
+		return nil, fmt.Errorf("%w: %v", ErrInvalidPurpose, purpose)
+	}
 }