/
parallelize.go
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/
parallelize.go
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// Copyright 2020-2021 Dolthub, Inc.
//
// 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 analyzer
import (
"strconv"
"github.com/go-kit/kit/metrics/discard"
"github.com/Ciyfly/FakerMysql/sql"
"github.com/Ciyfly/FakerMysql/sql/plan"
)
var (
// ParallelQueryCounter describes a metric that accumulates
// number of parallel queries monotonically.
ParallelQueryCounter = discard.NewCounter()
)
func shouldParallelize(node sql.Node, scope *Scope) bool {
// Don't parallelize subqueries, this can blow up the execution graph quickly
if len(scope.Schema()) > 0 {
return false
}
// Do not try to parallelize DDL or descriptive operations
return !plan.IsNoRowNode(node)
}
func parallelize(ctx *sql.Context, a *Analyzer, node sql.Node, scope *Scope) (sql.Node, error) {
if a.Parallelism <= 1 || !node.Resolved() {
return node, nil
}
proc, ok := node.(*plan.QueryProcess)
if (ok && !shouldParallelize(proc.Child, nil)) || !shouldParallelize(node, scope) {
return node, nil
}
node, err := plan.TransformUp(node, func(node sql.Node) (sql.Node, error) {
if !isParallelizable(node) {
return node, nil
}
ParallelQueryCounter.With("parallelism", strconv.Itoa(a.Parallelism)).Add(1)
return plan.NewExchange(a.Parallelism, node), nil
})
if err != nil {
return nil, err
}
return plan.TransformUp(node, removeRedundantExchanges)
}
// removeRedundantExchanges removes all the exchanges except for the topmost
// of all.
func removeRedundantExchanges(node sql.Node) (sql.Node, error) {
exchange, ok := node.(*plan.Exchange)
if !ok {
return node, nil
}
child, err := plan.TransformUp(exchange.Child, func(node sql.Node) (sql.Node, error) {
if exchange, ok := node.(*plan.Exchange); ok {
return exchange.Child, nil
}
return node, nil
})
if err != nil {
return nil, err
}
return exchange.WithChildren(child)
}
func isParallelizable(node sql.Node) bool {
var parallelizable = true
var tableSeen bool
var lastWasTable bool
plan.Inspect(node, func(node sql.Node) bool {
if node == nil {
return true
}
lastWasTable = false
if plan.IsBinary(node) {
parallelizable = false
return false
}
switch node := node.(type) {
// These are the only unary nodes that can be parallelized. Any other
// unary nodes will not.
case *plan.TableAlias, *plan.Exchange:
// Some nodes may have subquery expressions that make them unparallelizable
case *plan.Project, *plan.Filter:
for _, e := range node.(sql.Expressioner).Expressions() {
sql.Inspect(e, func(e sql.Expression) bool {
if q, ok := e.(*plan.Subquery); ok {
subqueryParallelizable := true
plan.Inspect(q.Query, func(node sql.Node) bool {
if node == nil {
return true
}
subqueryParallelizable = isParallelizable(node)
return subqueryParallelizable
})
if !subqueryParallelizable {
parallelizable = false
}
return true
}
return true
})
}
// IndexedTablesAccess already uses an index for lookups, so parallelizing it won't help in most cases (and can
// blow up the query execution graph)
case *plan.IndexedTableAccess:
parallelizable = false
return false
case sql.Table:
lastWasTable = true
tableSeen = true
default:
parallelizable = false
return false
}
return true
})
return parallelizable && tableSeen && lastWasTable
}