135 lines
4.4 KiB
Go
135 lines
4.4 KiB
Go
// Copyright 2017 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package statistics
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import (
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"fmt"
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"sync/atomic"
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"github.com/juju/errors"
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"github.com/ngaut/log"
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"github.com/pingcap/tidb/context"
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"github.com/pingcap/tidb/ddl"
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"github.com/pingcap/tidb/infoschema"
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"github.com/pingcap/tidb/util/sqlexec"
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)
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type statsCache map[int64]*Table
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// Handle can update stats info periodically.
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type Handle struct {
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ctx context.Context
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// LastVersion is the latest update version before last lease. Exported for test.
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LastVersion uint64
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// PrevLastVersion is the latest update version before two lease. Exported for test.
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// We need this because for two tables, the smaller version may write later than the one with larger version.
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// We can read the version with lastTwoVersion if the diff between commit time and version is less than one lease.
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// PrevLastVersion will be assigned by LastVersion every time Update is called.
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PrevLastVersion uint64
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statsCache atomic.Value
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// ddlEventCh is a channel to notify a ddl operation has happened. It is sent only by owner and read by stats handle.
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ddlEventCh chan *ddl.Event
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// All the stats collector required by session are maintained in this list.
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listHead *SessionStatsCollector
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// We collect the delta map and merge them with globalMap.
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globalMap tableDeltaMap
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}
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// Clear the statsCache, only for test.
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func (h *Handle) Clear() {
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h.statsCache.Store(statsCache{})
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h.LastVersion = 0
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h.PrevLastVersion = 0
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}
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// NewHandle creates a Handle for update stats.
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func NewHandle(ctx context.Context) *Handle {
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handle := &Handle{
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ctx: ctx,
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ddlEventCh: make(chan *ddl.Event, 100),
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listHead: &SessionStatsCollector{mapper: make(tableDeltaMap)},
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globalMap: make(tableDeltaMap),
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}
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handle.statsCache.Store(statsCache{})
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return handle
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}
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// Update reads stats meta from store and updates the stats map.
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func (h *Handle) Update(is infoschema.InfoSchema) error {
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sql := fmt.Sprintf("SELECT version, table_id, count from mysql.stats_meta where version > %d order by version", h.PrevLastVersion)
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rows, _, err := h.ctx.(sqlexec.RestrictedSQLExecutor).ExecRestrictedSQL(h.ctx, sql)
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if err != nil {
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return errors.Trace(err)
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}
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h.PrevLastVersion = h.LastVersion
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tables := make([]*Table, 0, len(rows))
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deletedTableIDs := make([]int64, 0, len(rows))
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for _, row := range rows {
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version, tableID, count := row.Data[0].GetUint64(), row.Data[1].GetInt64(), row.Data[2].GetInt64()
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table, ok := is.TableByID(tableID)
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if !ok {
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log.Debugf("Unknown table ID %d in stats meta table, maybe it has been dropped", tableID)
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deletedTableIDs = append(deletedTableIDs, tableID)
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continue
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}
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tableInfo := table.Meta()
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tbl, err := h.tableStatsFromStorage(tableInfo, count)
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// Error is not nil may mean that there are some ddl changes on this table, we will not update it.
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if err != nil {
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log.Errorf("Error occurred when read table stats for table id %d. The error message is %s.", tableID, err.Error())
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continue
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}
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if tbl == nil {
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deletedTableIDs = append(deletedTableIDs, tableID)
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continue
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}
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tables = append(tables, tbl)
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h.LastVersion = version
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}
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h.UpdateTableStats(tables, deletedTableIDs)
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return nil
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}
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// GetTableStats retrieves the statistics table from cache, and the cache will be updated by a goroutine.
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func (h *Handle) GetTableStats(tblID int64) *Table {
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tbl, ok := h.statsCache.Load().(statsCache)[tblID]
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if !ok {
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return PseudoTable(tblID)
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}
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return tbl
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}
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func (h *Handle) copyFromOldCache() statsCache {
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newCache := statsCache{}
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oldCache := h.statsCache.Load().(statsCache)
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for k, v := range oldCache {
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newCache[k] = v
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}
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return newCache
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}
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// UpdateTableStats updates the statistics table cache using copy on write.
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func (h *Handle) UpdateTableStats(tables []*Table, deletedIDs []int64) {
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newCache := h.copyFromOldCache()
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for _, tbl := range tables {
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id := tbl.TableID
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newCache[id] = tbl
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}
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for _, id := range deletedIDs {
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delete(newCache, id)
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}
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h.statsCache.Store(newCache)
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}
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