tablet_data.go

/*
Copyright 2019 The Vitess Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package vtctld

import (
	"flag"
	"io"
	"sync"
	"time"

	"context"

	"vitess.io/vitess/go/vt/grpcclient"
	"vitess.io/vitess/go/vt/log"
	"vitess.io/vitess/go/vt/topo"
	"vitess.io/vitess/go/vt/topo/topoproto"
	"vitess.io/vitess/go/vt/vttablet/tabletconn"

	querypb "vitess.io/vitess/go/vt/proto/query"
	topodatapb "vitess.io/vitess/go/vt/proto/topodata"
)

// This file maintains a tablet health cache. It establishes streaming
// connections with tablets, and updates its internal state with the
// result.

var (
	tabletHealthKeepAlive = flag.Duration("tablet_health_keep_alive", 5*time.Minute, "close streaming tablet health connection if there are no requests for this long")
)

type tabletHealth struct {
	mu sync.Mutex

	// result stores the most recent response.
	result *querypb.StreamHealthResponse
	// accessed stores the time of the most recent access.
	accessed time.Time

	// err stores the result of the stream attempt.
	err error
	// done is closed when the stream attempt ends.
	done chan struct{}
	// ready is closed when there is at least one result to read.
	ready chan struct{}
}

func newTabletHealth() *tabletHealth {
	return &tabletHealth{
		accessed: time.Now(),
		ready:    make(chan struct{}),
		done:     make(chan struct{}),
	}
}

func (th *tabletHealth) lastResult(ctx context.Context) (*querypb.StreamHealthResponse, error) {
	// Wait until at least the first result comes in, or the stream ends.
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case <-th.ready:
	case <-th.done:
	}

	th.mu.Lock()
	defer th.mu.Unlock()

	th.accessed = time.Now()
	return th.result, th.err
}

func (th *tabletHealth) lastAccessed() time.Time {
	th.mu.Lock()
	defer th.mu.Unlock()

	return th.accessed
}

func (th *tabletHealth) stream(ctx context.Context, ts *topo.Server, tabletAlias *topodatapb.TabletAlias) (err error) {
	defer func() {
		th.mu.Lock()
		th.err = err
		th.mu.Unlock()
		close(th.done)
	}()

	ti, err := ts.GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}

	conn, err := tabletconn.GetDialer()(ti.Tablet, grpcclient.FailFast(true))
	if err != nil {
		return err
	}
	defer conn.Close(ctx)

	first := true
	return conn.StreamHealth(ctx, func(shr *querypb.StreamHealthResponse) error {
		th.mu.Lock()
		th.result = shr
		th.mu.Unlock()

		if first {
			// We got the first result, so we're ready to be accessed.
			close(th.ready)
			first = false
		}
		if time.Since(th.lastAccessed()) >= *tabletHealthKeepAlive {
			return io.EOF
		}
		return nil
	})
}

type tabletHealthCache struct {
	ts *topo.Server

	// mu protects the map.
	mu sync.Mutex

	// tabletMap is keyed by topoproto.TabletAliasString(tablet alias).
	tabletMap map[string]*tabletHealth
}

func newTabletHealthCache(ts *topo.Server) *tabletHealthCache {
	return &tabletHealthCache{
		ts:        ts,
		tabletMap: make(map[string]*tabletHealth),
	}
}

func (thc *tabletHealthCache) Get(ctx context.Context, tabletAlias *topodatapb.TabletAlias) (*querypb.StreamHealthResponse, error) {
	thc.mu.Lock()

	tabletAliasStr := topoproto.TabletAliasString(tabletAlias)
	th, ok := thc.tabletMap[tabletAliasStr]
	if !ok {
		// No existing stream, so start one.
		th = newTabletHealth()
		thc.tabletMap[tabletAliasStr] = th

		go func() {
			log.Infof("starting health stream for tablet %v", tabletAlias)
			err := th.stream(context.Background(), thc.ts, tabletAlias)
			log.Infof("tablet %v health stream ended, error: %v", tabletAlias, err)
			thc.delete(tabletAliasStr)
		}()
	}

	thc.mu.Unlock()

	return th.lastResult(ctx)
}

func (thc *tabletHealthCache) delete(tabletAliasStr string) {
	thc.mu.Lock()
	delete(thc.tabletMap, tabletAliasStr)
	thc.mu.Unlock()
}