Move concurrent connection dial limit out of healthcheck.

go/flags/endtoend/mysqlctld.txt

@@ -61,6 +61,7 @@ Flags:
       --db_tls_min_version string                                        Configures the minimal TLS version negotiated when SSL is enabled. Defaults to TLSv1.2. Options: TLSv1.0, TLSv1.1, TLSv1.2, TLSv1.3.
       --dba_idle_timeout duration                                        Idle timeout for dba connections (default 1m0s)
       --dba_pool_size int                                                Size of the connection pool for dba connections (default 20)
+      --grpc-dial-concurrency-limit int                                  Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc_auth_mode string                                            Which auth plugin implementation to use (eg: static)
       --grpc_auth_mtls_allowed_substrings string                         List of substrings of at least one of the client certificate names (separated by colon).
       --grpc_auth_static_client_creds string                             When using grpc_static_auth in the server, this file provides the credentials to use to authenticate with server.

go/flags/endtoend/vtbackup.txt

@@ -128,6 +128,7 @@ Flags:
       --file_backup_storage_root string                             Root directory for the file backup storage.
       --gcs_backup_storage_bucket string                            Google Cloud Storage bucket to use for backups.
       --gcs_backup_storage_root string                              Root prefix for all backup-related object names.
+      --grpc-dial-concurrency-limit int                             Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc_auth_static_client_creds string                        When using grpc_static_auth in the server, this file provides the credentials to use to authenticate with server.
       --grpc_compression string                                     Which protocol to use for compressing gRPC. Default: nothing. Supported: snappy
       --grpc_enable_tracing                                         Enable gRPC tracing.

go/flags/endtoend/vtcombo.txt

@@ -167,7 +167,6 @@ Flags:
       --grpc_server_keepalive_timeout duration                           After having pinged for keepalive check, the server waits for a duration of Timeout and if no activity is seen even after that the connection is closed. (default 10s)
       --grpc_use_effective_callerid                                      If set, and SSL is not used, will set the immediate caller id from the effective caller id's principal.
       --health_check_interval duration                                   Interval between health checks (default 20s)
-      --healthcheck-dial-concurrency int                                 Maximum concurrency of new healthcheck connections. This should be less than the golang max thread limit of 10000. (default 1024)
       --healthcheck_retry_delay duration                                 health check retry delay (default 2ms)
       --healthcheck_timeout duration                                     the health check timeout period (default 1m0s)
       --heartbeat_enable                                                 If true, vttablet records (if master) or checks (if replica) the current time of a replication heartbeat in the sidecar database's heartbeat table. The result is used to inform the serving state of the vttablet via healthchecks.

go/flags/endtoend/vtctlclient.txt

@@ -9,6 +9,7 @@ Usage of vtctlclient:
       --config-type string                                          Config file type (omit to infer config type from file extension).
       --datadog-agent-host string                                   host to send spans to. if empty, no tracing will be done
       --datadog-agent-port string                                   port to send spans to. if empty, no tracing will be done
+      --grpc-dial-concurrency-limit int                             Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc_auth_static_client_creds string                        When using grpc_static_auth in the server, this file provides the credentials to use to authenticate with server.
       --grpc_compression string                                     Which protocol to use for compressing gRPC. Default: nothing. Supported: snappy
       --grpc_enable_tracing                                         Enable gRPC tracing.

go/flags/endtoend/vtctld.txt

@@ -57,6 +57,7 @@ Flags:
       --file_backup_storage_root string                                  Root directory for the file backup storage.
       --gcs_backup_storage_bucket string                                 Google Cloud Storage bucket to use for backups.
       --gcs_backup_storage_root string                                   Root prefix for all backup-related object names.
+      --grpc-dial-concurrency-limit int                                  Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc_auth_mode string                                            Which auth plugin implementation to use (eg: static)
       --grpc_auth_mtls_allowed_substrings string                         List of substrings of at least one of the client certificate names (separated by colon).
       --grpc_auth_static_client_creds string                             When using grpc_static_auth in the server, this file provides the credentials to use to authenticate with server.
@@ -85,7 +86,6 @@ Flags:
       --grpc_server_keepalive_enforcement_policy_permit_without_stream   gRPC server permit client keepalive pings even when there are no active streams (RPCs)
       --grpc_server_keepalive_time duration                              After a duration of this time, if the server doesn't see any activity, it pings the client to see if the transport is still alive. (default 10s)
       --grpc_server_keepalive_timeout duration                           After having pinged for keepalive check, the server waits for a duration of Timeout and if no activity is seen even after that the connection is closed. (default 10s)
-      --healthcheck-dial-concurrency int                                 Maximum concurrency of new healthcheck connections. This should be less than the golang max thread limit of 10000. (default 1024)
   -h, --help                                                             help for vtctld
       --jaeger-agent-host string                                         host and port to send spans to. if empty, no tracing will be done
       --keep_logs duration                                               keep logs for this long (using ctime) (zero to keep forever)

go/flags/endtoend/vtgate.txt

@@ -64,6 +64,7 @@ Flags:
       --foreign_key_mode string                                          This is to provide how to handle foreign key constraint in create/alter table. Valid values are: allow, disallow (default "allow")
       --gate_query_cache_memory int                                      gate server query cache size in bytes, maximum amount of memory to be cached. vtgate analyzes every incoming query and generate a query plan, these plans are being cached in a lru cache. This config controls the capacity of the lru cache. (default 33554432)
       --gateway_initial_tablet_timeout duration                          At startup, the tabletGateway will wait up to this duration to get at least one tablet per keyspace/shard/tablet type (default 30s)
+      --grpc-dial-concurrency-limit int                                  Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc-send-session-in-streaming                                   If set, will send the session as last packet in streaming api to support transactions in streaming
       --grpc-use-effective-groups                                        If set, and SSL is not used, will set the immediate caller's security groups from the effective caller id's groups.
       --grpc-use-static-authentication-callerid                          If set, will set the immediate caller id to the username authenticated by the static auth plugin.
@@ -96,7 +97,6 @@ Flags:
       --grpc_server_keepalive_time duration                              After a duration of this time, if the server doesn't see any activity, it pings the client to see if the transport is still alive. (default 10s)
       --grpc_server_keepalive_timeout duration                           After having pinged for keepalive check, the server waits for a duration of Timeout and if no activity is seen even after that the connection is closed. (default 10s)
       --grpc_use_effective_callerid                                      If set, and SSL is not used, will set the immediate caller id from the effective caller id's principal.
-      --healthcheck-dial-concurrency int                                 Maximum concurrency of new healthcheck connections. This should be less than the golang max thread limit of 10000. (default 1024)
       --healthcheck_retry_delay duration                                 health check retry delay (default 2ms)
       --healthcheck_timeout duration                                     the health check timeout period (default 1m0s)
   -h, --help                                                             help for vtgate

go/flags/endtoend/vtgateclienttest.txt

@@ -14,6 +14,7 @@ Flags:
       --config-persistence-min-interval duration                         minimum interval between persisting dynamic config changes back to disk (if no change has occurred, nothing is done). (default 1s)
       --config-type string                                               Config file type (omit to infer config type from file extension).
       --default_tablet_type topodatapb.TabletType                        The default tablet type to set for queries, when one is not explicitly selected. (default PRIMARY)
+      --grpc-dial-concurrency-limit int                                  Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc_auth_mode string                                            Which auth plugin implementation to use (eg: static)
       --grpc_auth_mtls_allowed_substrings string                         List of substrings of at least one of the client certificate names (separated by colon).
       --grpc_auth_static_client_creds string                             When using grpc_static_auth in the server, this file provides the credentials to use to authenticate with server.

go/flags/endtoend/vtorc.txt

@@ -34,6 +34,7 @@ Flags:
       --config-type string                                          Config file type (omit to infer config type from file extension).
       --consul_auth_static_file string                              JSON File to read the topos/tokens from.
       --emit_stats                                                  If set, emit stats to push-based monitoring and stats backends
+      --grpc-dial-concurrency-limit int                             Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc_auth_static_client_creds string                        When using grpc_static_auth in the server, this file provides the credentials to use to authenticate with server.
       --grpc_compression string                                     Which protocol to use for compressing gRPC. Default: nothing. Supported: snappy
       --grpc_enable_tracing                                         Enable gRPC tracing.

go/flags/endtoend/vttablet.txt

@@ -166,6 +166,7 @@ Flags:
       --gcs_backup_storage_bucket string                                 Google Cloud Storage bucket to use for backups.
       --gcs_backup_storage_root string                                   Root prefix for all backup-related object names.
       --gh-ost-path string                                               override default gh-ost binary full path (default "gh-ost")
+      --grpc-dial-concurrency-limit int                                  Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc_auth_mode string                                            Which auth plugin implementation to use (eg: static)
       --grpc_auth_mtls_allowed_substrings string                         List of substrings of at least one of the client certificate names (separated by colon).
       --grpc_auth_static_client_creds string                             When using grpc_static_auth in the server, this file provides the credentials to use to authenticate with server.

go/flags/endtoend/vttestserver.txt

@@ -43,6 +43,7 @@ Flags:
       --external_topo_implementation string                              the topology implementation to use for vtcombo process
       --extra_my_cnf string                                              extra files to add to the config, separated by ':'
       --foreign_key_mode string                                          This is to provide how to handle foreign key constraint in create/alter table. Valid values are: allow, disallow (default "allow")
+      --grpc-dial-concurrency-limit int                                  Maximum concurrency of grpc dial operations. This should be less than the golang max thread limit of 10000. (default 1024)
       --grpc_auth_mode string                                            Which auth plugin implementation to use (eg: static)
       --grpc_auth_mtls_allowed_substrings string                         List of substrings of at least one of the client certificate names (separated by colon).
       --grpc_auth_static_client_creds string                             When using grpc_static_auth in the server, this file provides the credentials to use to authenticate with server.

go/vt/discovery/healthcheck.go

@@ -46,7 +46,6 @@ import (
 	"github.com/google/safehtml/template"
 	"github.com/google/safehtml/template/uncheckedconversions"
 	"github.com/spf13/pflag"
-	"golang.org/x/sync/semaphore"
 
 	"vitess.io/vitess/go/flagutil"
 	"vitess.io/vitess/go/netutil"
@@ -92,9 +91,6 @@ var (
 	// refreshKnownTablets tells us whether to process all tablets or only new tablets.
 	refreshKnownTablets = true
 
-	// healthCheckDialConcurrency tells us how many healthcheck connections can be opened to tablets at once. This should be less than the golang max thread limit of 10000.
-	healthCheckDialConcurrency int64 = 1024
-
 	// How much to sleep between each check.
 	waitAvailableTabletInterval = 100 * time.Millisecond
 
@@ -177,7 +173,6 @@ func registerWebUIFlags(fs *pflag.FlagSet) {
 	fs.StringVar(&TabletURLTemplateString, "tablet_url_template", "http://{{.GetTabletHostPort}}", "Format string describing debug tablet url formatting. See getTabletDebugURL() for how to customize this.")
 	fs.DurationVar(&refreshInterval, "tablet_refresh_interval", 1*time.Minute, "Tablet refresh interval.")
 	fs.BoolVar(&refreshKnownTablets, "tablet_refresh_known_tablets", true, "Whether to reload the tablet's address/port map from topo in case they change.")
-	fs.Int64Var(&healthCheckDialConcurrency, "healthcheck-dial-concurrency", 1024, "Maximum concurrency of new healthcheck connections. This should be less than the golang max thread limit of 10000.")
 	ParseTabletURLTemplateFromFlag()
 }
 
@@ -297,8 +292,6 @@ type HealthCheckImpl struct {
 	subscribers map[chan *TabletHealth]struct{}
 	// loadTablets trigger is used to immediately load a new primary tablet when the current one has been demoted
 	loadTabletsTrigger chan struct{}
-	// healthCheckDialSem is used to limit how many healthcheck connections can be opened to tablets at once.
-	healthCheckDialSem *semaphore.Weighted
 }
 
 // NewHealthCheck creates a new HealthCheck object.
@@ -333,7 +326,6 @@ func NewHealthCheck(ctx context.Context, retryDelay, healthCheckTimeout time.Dur
 		cell:               localCell,
 		retryDelay:         retryDelay,
 		healthCheckTimeout: healthCheckTimeout,
-		healthCheckDialSem: semaphore.NewWeighted(healthCheckDialConcurrency),
 		healthByAlias:      make(map[tabletAliasString]*tabletHealthCheck),
 		healthData:         make(map[KeyspaceShardTabletType]map[tabletAliasString]*TabletHealth),
 		healthy:            make(map[KeyspaceShardTabletType][]*TabletHealth),
@@ -844,7 +836,7 @@ func (hc *HealthCheckImpl) TabletConnection(ctx context.Context, alias *topodata
 		// TODO: test that throws this error
 		return nil, vterrors.Errorf(vtrpc.Code_NOT_FOUND, "tablet: %v is either down or nonexistent", alias)
 	}
-	return thc.Connection(ctx, hc), nil
+	return thc.Connection(ctx), nil
 }
 
 // getAliasByCell should only be called while holding hc.mu

go/vt/discovery/tablet_health_check.go

@@ -19,7 +19,6 @@ package discovery
 import (
 	"context"
 	"fmt"
-	"net"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -34,16 +33,12 @@ import (
 	"vitess.io/vitess/go/vt/vttablet/queryservice"
 	"vitess.io/vitess/go/vt/vttablet/tabletconn"
 
-	"google.golang.org/grpc"
 	"google.golang.org/protobuf/proto"
 
 	"vitess.io/vitess/go/vt/proto/query"
 	"vitess.io/vitess/go/vt/proto/topodata"
 )
 
-// withDialerContextOnce ensures grpc.WithDialContext() is added once to the options.
-var withDialerContextOnce sync.Once
-
 // tabletHealthCheck maintains the health status of a tablet. A map of this
 // structure is maintained in HealthCheck.
 type tabletHealthCheck struct {
@@ -127,8 +122,8 @@ func (thc *tabletHealthCheck) setServingState(serving bool, reason string) {
 }
 
 // stream streams healthcheck responses to callback.
-func (thc *tabletHealthCheck) stream(ctx context.Context, hc *HealthCheckImpl, callback func(*query.StreamHealthResponse) error) error {
-	conn := thc.Connection(ctx, hc)
+func (thc *tabletHealthCheck) stream(ctx context.Context, callback func(*query.StreamHealthResponse) error) error {
+	conn := thc.Connection(ctx)
 	if conn == nil {
 		// This signals the caller to retry
 		return nil
@@ -141,34 +136,14 @@ func (thc *tabletHealthCheck) stream(ctx context.Context, hc *HealthCheckImpl, c
 	return err
 }
 
-func (thc *tabletHealthCheck) Connection(ctx context.Context, hc *HealthCheckImpl) queryservice.QueryService {
+func (thc *tabletHealthCheck) Connection(ctx context.Context) queryservice.QueryService {
 	thc.connMu.Lock()
 	defer thc.connMu.Unlock()
-	return thc.connectionLocked(ctx, hc)
-}
-
-func healthCheckDialerFactory(hc *HealthCheckImpl) func(ctx context.Context, addr string) (net.Conn, error) {
-	return func(ctx context.Context, addr string) (net.Conn, error) {
-		// Limit the number of healthcheck connections opened in parallel to avoid high OS-thread
-		// usage due to blocking networking syscalls (eg: DNS lookups, TCP connection opens,
-		// etc). Without this limit it is possible for vtgates watching >10k tablets to hit
-		// the panic: 'runtime: program exceeds 10000-thread limit'.
-		if err := hc.healthCheckDialSem.Acquire(ctx, 1); err != nil {
-			return nil, err
-		}
-		defer hc.healthCheckDialSem.Release(1)
-		var dialer net.Dialer
-		return dialer.DialContext(ctx, "tcp", addr)
-	}
+	return thc.connectionLocked(ctx)
 }
 
-func (thc *tabletHealthCheck) connectionLocked(ctx context.Context, hc *HealthCheckImpl) queryservice.QueryService {
+func (thc *tabletHealthCheck) connectionLocked(ctx context.Context) queryservice.QueryService {
 	if thc.Conn == nil {
-		withDialerContextOnce.Do(func() {
-			grpcclient.RegisterGRPCDialOptions(func(opts []grpc.DialOption) ([]grpc.DialOption, error) {
-				return append(opts, grpc.WithContextDialer(healthCheckDialerFactory(hc))), nil
-			})
-		})
 		conn, err := tabletconn.GetDialer()(ctx, thc.Tablet, grpcclient.FailFast(true))
 		if err != nil {
 			thc.LastError = err
@@ -297,7 +272,7 @@ func (thc *tabletHealthCheck) checkConn(hc *HealthCheckImpl) {
 		}()
 
 		// Read stream health responses.
-		err := thc.stream(streamCtx, hc, func(shr *query.StreamHealthResponse) error {
+		err := thc.stream(streamCtx, func(shr *query.StreamHealthResponse) error {
 			// We received a message. Reset the back-off.
 			retryDelay = hc.retryDelay
 			// Don't block on send to avoid deadlocks.