[release-17.0] [VTAdmin API] Fix schema cache flag, add documentation (#15704)

doc/vtadmin/clusters.yaml

@@ -54,3 +54,24 @@ defaults:
  # - schema-read-pool => for GetSchema, GetSchemas, and FindSchema api methods
  # - topo-read-pool => for generic topo methods (e.g. GetKeyspace, FindAllShardsInKeyspace)
  # - workflow-read-pool => for GetWorkflow/GetWorkflows api methods.
+
+ # How long to keep values in schema cache by default (duration passed to Add takes precedence).
+ # A value of "0m" means values will never be cached, a positive duration "1m" means items will be cached
+ # for that duration, and passing nothing will default to "NoExpiration".
+ schema-cache-default-expiration: 1m
+ # How many outstanding backfil requests to permit in schema cache.
+ # If the queue is full, calls backfill schemas will return false, and those requests will be discarded.
+ # A value of "0" means that the underlying channel will have a size of 0, 
+ # and every send to the backfill queue will block until the queue is "empty" again.
+ schema-cache-backfill-queue-size: 0
+ # How often expired values are removed from schema cache.
+ schema-cache-cleanup-interval: 5m
+ # How long a backfill request is considered valid.
+ # If the backfill goroutin encounters a request older than this, it is discarded.
+ schema-cache-backfill-request-ttl: 100ms
+ # How much time must pass before the backfill goroutine will re-backfill the same key.
+ # Used to prevent multiple callers from queueing up too many requests for the same key,
+ # when one backfill would satisfy all of them.
+ schema-cache-backfill-request-duplicate-interval: 1m
+ # How long to wait whe attempting to enqueue a backfill request before giving up.
+ schema-cache-backfill-enqueue-wait-time: 50ms

go/vt/vtadmin/cache/cache.go

@@ -54,6 +54,9 @@ const (
  // backfill requests to still process, if a config is passed with a
  // non-positive BackfillRequestTTL.
  DefaultBackfillRequestTTL = time.Millisecond * 100
+ // DefaultBackfillQueueSize is the default value used for the size of the
+ // backfill queue, if a config is passed with a non-positive BackfillQueueSize.
+ DefaultBackfillQueueSize = 0
 )
 
 // Config is the configuration for a cache.
@@ -125,6 +128,11 @@ func New[Key Keyer, Value any](fillFunc func(ctx context.Context, req Key) (Valu
  cfg.BackfillRequestTTL = DefaultBackfillRequestTTL
  }
 
+ if cfg.BackfillQueueSize < 0 {
+ log.Warningf("BackfillQueueSize (%v) must be positive, defaulting to %v", cfg.BackfillQueueSize, DefaultBackfillQueueSize)
+ cfg.BackfillQueueSize = DefaultBackfillQueueSize
+ }
+
  c := &Cache[Key, Value]{
  cache: cache.New(cfg.DefaultExpiration, cfg.CleanupInterval),
  lastFill: map[string]time.Time{},

go/vt/vtadmin/cache/cache_test.go

@@ -93,6 +93,45 @@ func TestBackfillDuplicates(t *testing.T) {
  }
 }
 
+func TestBackfillQueueSize(t *testing.T) {
+ t.Parallel()
+
+ tests := []struct {
+ name string
+ configuredBackfillQueueSize int
+ expectedBackfillQueueSize int
+ }{
+ {
+ name: "configured negative backfill queue size",
+ configuredBackfillQueueSize: -1,
+ expectedBackfillQueueSize: 0,
+ }, {
+ name: "configured 0 backfill queue size",
+ configuredBackfillQueueSize: 0,
+ expectedBackfillQueueSize: 0,
+ }, {
+ name: "configured positive backfill queue size",
+ configuredBackfillQueueSize: 1,
+ expectedBackfillQueueSize: 1,
+ },
+ }
+ for _, tt := range tests {
+ tt := tt
+
+ t.Run(tt.name, func(t *testing.T) {
+ t.Parallel()
+
+ c := cache.New(func(ctx context.Context, req intkey) (any, error) {
+ return nil, nil
+ }, cache.Config{
+ BackfillQueueSize: tt.configuredBackfillQueueSize,
+ })
+ var config cache.Config = c.Debug()["config"].(cache.Config)
+ assert.Equal(t, tt.expectedBackfillQueueSize, config.BackfillQueueSize)
+ })
+ }
+}
+
 func TestBackfillTTL(t *testing.T) {
  t.Parallel()
 

go/vt/vtadmin/cluster/cluster.go

@@ -1424,7 +1424,10 @@ func (c *Cluster) GetSchemas(ctx context.Context, opts GetSchemaOptions) ([]*vta
 
  span.Annotate("cache_hit", ok)
  if ok {
+ log.Infof("GetSchemas(cluster = %s) fetching schemas from schema cache", c.ID)
  return schemas, err
+ } else {
+ log.Infof("GetSchemas(cluster = %s) bypassing schema cache", c.ID)
  }
  }