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explain.go
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explain.go
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// Copyright 2015 The Cockroach 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.
//
// Author: Peter Mattis (peter@cockroachlabs.com)
package sql
import (
"fmt"
"strings"
"golang.org/x/net/context"
"github.com/cockroachdb/cockroach/pkg/internal/client"
"github.com/cockroachdb/cockroach/pkg/roachpb"
"github.com/cockroachdb/cockroach/pkg/sql/distsqlrun"
"github.com/cockroachdb/cockroach/pkg/sql/parser"
"github.com/cockroachdb/cockroach/pkg/sql/sqlbase"
)
type explainMode int
const (
explainNone explainMode = iota
explainDebug
explainPlan
explainTrace
// explainDistSQL shows the physical distsql plan for a query and whether a
// query would be run in "auto" DISTSQL mode. See explainDistSQLNode for
// details.
explainDistSQL
)
var explainStrings = map[explainMode]string{
explainDebug: "debug",
explainPlan: "plan",
explainTrace: "trace",
explainDistSQL: "distsql",
}
// Explain executes the explain statement, providing debugging and analysis
// info about the wrapped statement.
//
// Privileges: the same privileges as the statement being explained.
func (p *planner) Explain(ctx context.Context, n *parser.Explain) (planNode, error) {
mode := explainNone
optimized := true
expanded := true
normalizeExprs := true
explainer := explainer{
showMetadata: false,
showExprs: false,
showTypes: false,
doIndent: false,
}
for _, opt := range n.Options {
optLower := strings.ToLower(opt)
newMode := explainNone
// Search for the string in `explainStrings`.
for mode, modeStr := range explainStrings {
if optLower == modeStr {
newMode = mode
break
}
}
if newMode == explainNone {
switch optLower {
case "types":
newMode = explainPlan
explainer.showExprs = true
explainer.showTypes = true
// TYPES implies METADATA.
explainer.showMetadata = true
case "indent":
explainer.doIndent = true
case "symvars":
explainer.symbolicVars = true
case "metadata":
explainer.showMetadata = true
case "qualify":
explainer.qualifyNames = true
case "verbose":
// VERBOSE implies EXPRS.
explainer.showExprs = true
// VERBOSE implies QUALIFY.
explainer.qualifyNames = true
// VERBOSE implies METADATA.
explainer.showMetadata = true
case "exprs":
explainer.showExprs = true
case "noexpand":
expanded = false
case "nonormalize":
normalizeExprs = false
case "nooptimize":
optimized = false
default:
return nil, fmt.Errorf("unsupported EXPLAIN option: %s", opt)
}
}
if newMode != explainNone {
if mode != explainNone {
return nil, fmt.Errorf("cannot set EXPLAIN mode more than once: %s", opt)
}
mode = newMode
}
}
if mode == explainNone {
mode = explainPlan
}
p.evalCtx.SkipNormalize = !normalizeExprs
plan, err := p.newPlan(ctx, n.Statement, nil)
if err != nil {
return nil, err
}
switch mode {
case explainDebug:
return &explainDebugNode{plan}, nil
case explainDistSQL:
return &explainDistSQLNode{
plan: plan,
distSQLPlanner: p.session.distSQLPlanner,
txn: p.txn,
}, nil
case explainPlan:
// We may want to show placeholder types, so ensure no values
// are missing.
p.semaCtx.Placeholders.FillUnassigned()
return p.makeExplainPlanNode(explainer, expanded, optimized, plan), nil
case explainTrace:
return p.makeTraceNode(plan), nil
default:
return nil, fmt.Errorf("unsupported EXPLAIN mode: %d", mode)
}
}
type debugValueType int
const (
// The debug values do not refer to a full result row.
debugValuePartial debugValueType = iota
// The debug values refer to a full result row but the row was filtered out.
debugValueFiltered
// The debug value refers to a full result row that has been stored in a buffer
// and will be emitted later.
debugValueBuffered
// The debug values refer to a full result row.
debugValueRow
)
func (t debugValueType) String() string {
switch t {
case debugValuePartial:
return "PARTIAL"
case debugValueFiltered:
return "FILTERED"
case debugValueBuffered:
return "BUFFERED"
case debugValueRow:
return "ROW"
default:
panic(fmt.Sprintf("invalid debugValueType %d", t))
}
}
// debugValues is a set of values used to implement EXPLAIN (DEBUG).
type debugValues struct {
rowIdx int
key string
value string
output debugValueType
}
func (vals *debugValues) AsRow() parser.Datums {
keyVal := parser.DNull
if vals.key != "" {
keyVal = parser.NewDString(vals.key)
}
// The "output" value is NULL for partial rows, or a DBool indicating if the row passed the
// filtering.
outputVal := parser.DNull
switch vals.output {
case debugValueFiltered:
outputVal = parser.MakeDBool(false)
case debugValueRow:
outputVal = parser.MakeDBool(true)
}
return parser.Datums{
parser.NewDInt(parser.DInt(vals.rowIdx)),
keyVal,
parser.NewDString(vals.value),
outputVal,
}
}
// explainDebugNode is a planNode that wraps another node and converts DebugValues() results to a
// row of Values(). It is used as the top-level node for EXPLAIN (DEBUG) statements.
type explainDebugNode struct {
plan planNode
}
// Columns for explainDebug mode.
var debugColumns = sqlbase.ResultColumns{
{Name: "RowIdx", Typ: parser.TypeInt},
{Name: "Key", Typ: parser.TypeString},
{Name: "Value", Typ: parser.TypeString},
{Name: "Disposition", Typ: parser.TypeString},
}
func (*explainDebugNode) Columns() sqlbase.ResultColumns { return debugColumns }
func (*explainDebugNode) Ordering() orderingInfo { return orderingInfo{} }
func (n *explainDebugNode) Start(ctx context.Context) error { return n.plan.Start(ctx) }
func (n *explainDebugNode) Next(ctx context.Context) (bool, error) { return n.plan.Next(ctx) }
func (n *explainDebugNode) Close(ctx context.Context) { n.plan.Close(ctx) }
func (n *explainDebugNode) Spans(ctx context.Context) (_, _ roachpb.Spans, _ error) {
return n.plan.Spans(ctx)
}
func (n *explainDebugNode) Values() parser.Datums {
vals := n.plan.DebugValues()
keyVal := parser.DNull
if vals.key != "" {
keyVal = parser.NewDString(vals.key)
}
return parser.Datums{
parser.NewDInt(parser.DInt(vals.rowIdx)),
keyVal,
parser.NewDString(vals.value),
parser.NewDString(vals.output.String()),
}
}
func (*explainDebugNode) MarkDebug(_ explainMode) {}
func (*explainDebugNode) DebugValues() debugValues { return debugValues{} }
// explainDistSQLNode is a planNode that wraps a plan and returns
// information related to running that plan under DistSQL.
type explainDistSQLNode struct {
plan planNode
distSQLPlanner *distSQLPlanner
// txn is the current transaction (used for the fake span resolver).
txn *client.Txn
// The single row returned by the node.
values parser.Datums
// done is set if Next() was called.
done bool
}
func (*explainDistSQLNode) Ordering() orderingInfo { return orderingInfo{} }
func (*explainDistSQLNode) MarkDebug(_ explainMode) {}
func (*explainDistSQLNode) DebugValues() debugValues { return debugValues{} }
func (*explainDistSQLNode) Close(context.Context) {}
func (*explainDistSQLNode) Spans(context.Context) (_, _ roachpb.Spans, _ error) {
panic("unimplemented")
}
var explainDistSQLColumns = sqlbase.ResultColumns{
{Name: "Automatic", Typ: parser.TypeBool},
{Name: "URL", Typ: parser.TypeString},
{Name: "JSON", Typ: parser.TypeString},
}
func (*explainDistSQLNode) Columns() sqlbase.ResultColumns { return explainDistSQLColumns }
func (n *explainDistSQLNode) Start(ctx context.Context) error {
// Trigger limit propagation.
setUnlimited(n.plan)
auto, err := n.distSQLPlanner.CheckSupport(n.plan)
if err != nil {
return err
}
planCtx := n.distSQLPlanner.NewPlanningCtx(ctx, n.txn)
plan, err := n.distSQLPlanner.createPlanForNode(&planCtx, n.plan)
if err != nil {
return err
}
n.distSQLPlanner.FinalizePlan(&planCtx, &plan)
flows := plan.GenerateFlowSpecs()
planJSON, planURL, err := distsqlrun.GeneratePlanDiagramWithURL(flows)
if err != nil {
return err
}
n.values = parser.Datums{
parser.MakeDBool(parser.DBool(auto)),
parser.NewDString(planURL.String()),
parser.NewDString(planJSON),
}
return nil
}
func (n *explainDistSQLNode) Next(context.Context) (bool, error) {
if n.done {
return false, nil
}
n.done = true
return true, nil
}
func (n *explainDistSQLNode) Values() parser.Datums {
return n.values
}