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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"
"github.com/cockroachdb/cockroach/roachpb"
"github.com/cockroachdb/cockroach/sql/parser"
"github.com/cockroachdb/cockroach/util/encoding"
"github.com/cockroachdb/cockroach/util/tracing"
basictracer "github.com/opentracing/basictracer-go"
opentracing "github.com/opentracing/opentracing-go"
)
type explainMode int
const (
explainNone explainMode = iota
explainDebug
explainPlan
explainTrace
)
// Explain executes the explain statement, providing debugging and analysis
// info about a DELETE, INSERT, SELECT or UPDATE statement.
//
// Privileges: the same privileges as the statement being explained.
func (p *planner) Explain(n *parser.Explain, autoCommit bool) (planNode, *roachpb.Error) {
mode := explainNone
if len(n.Options) == 1 {
if strings.EqualFold(n.Options[0], "DEBUG") {
mode = explainDebug
} else if strings.EqualFold(n.Options[0], "TRACE") {
mode = explainTrace
}
} else if len(n.Options) == 0 {
mode = explainPlan
}
if mode == explainNone {
return nil, roachpb.NewUErrorf("unsupported EXPLAIN options: %s", n)
}
if mode == explainTrace {
sp, err := tracing.JoinOrNewSnowball("coordinator", nil, func(sp basictracer.RawSpan) {
p.txn.CollectedSpans = append(p.txn.CollectedSpans, sp)
})
if err != nil {
return nil, roachpb.NewError(err)
}
p.txn.Context = opentracing.ContextWithSpan(p.txn.Context, sp)
}
plan, err := p.makePlan(n.Statement, autoCommit)
if err != nil {
return nil, err
}
switch mode {
case explainDebug:
plan.MarkDebug(mode)
// Wrap the plan in an explainDebugNode.
return &explainDebugNode{plan}, nil
case explainPlan:
v := &valuesNode{}
v.columns = []ResultColumn{
{Name: "Level", Typ: parser.DummyInt},
{Name: "Type", Typ: parser.DummyString},
{Name: "Description", Typ: parser.DummyString},
}
populateExplain(v, plan, 0)
return v, nil
case explainTrace:
plan.MarkDebug(explainDebug)
return (&sortNode{
ordering: []columnOrderInfo{{len(traceColumns), encoding.Ascending}, {2, encoding.Ascending}},
columns: traceColumns,
}).wrap(&explainTraceNode{plan: plan, txn: p.txn}), nil
default:
return nil, roachpb.NewUErrorf("unsupported EXPLAIN mode: %d", mode)
}
}
func populateExplain(v *valuesNode, plan planNode, level int) {
name, description, children := plan.ExplainPlan()
row := parser.DTuple{
parser.DInt(level),
parser.DString(name),
parser.DString(description),
}
v.rows = append(v.rows, row)
for _, child := range children {
populateExplain(v, child, level+1)
}
}
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.DTuple {
keyVal := parser.DNull
if vals.key != "" {
keyVal = parser.DString(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.DBool(false)
case debugValueRow:
outputVal = parser.DBool(true)
}
return parser.DTuple{
parser.DInt(vals.rowIdx),
keyVal,
parser.DString(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 = []ResultColumn{
{Name: "RowIdx", Typ: parser.DummyInt},
{Name: "Key", Typ: parser.DummyString},
{Name: "Value", Typ: parser.DummyString},
{Name: "Disposition", Typ: parser.DummyString},
}
func (*explainDebugNode) Columns() []ResultColumn { return debugColumns }
func (*explainDebugNode) Ordering() orderingInfo { return orderingInfo{} }
func (n *explainDebugNode) PErr() *roachpb.Error { return n.plan.PErr() }
func (n *explainDebugNode) Next() bool { return n.plan.Next() }
func (n *explainDebugNode) ExplainPlan() (name, description string, children []planNode) {
return n.plan.ExplainPlan()
}
func (n *explainDebugNode) Values() parser.DTuple {
vals := n.plan.DebugValues()
keyVal := parser.DNull
if vals.key != "" {
keyVal = parser.DString(vals.key)
}
return parser.DTuple{
parser.DInt(vals.rowIdx),
keyVal,
parser.DString(vals.value),
parser.DString(vals.output.String()),
}
}
func (*explainDebugNode) MarkDebug(_ explainMode) {
panic("debug mode not implemented in explainDebugNode")
}
func (*explainDebugNode) DebugValues() debugValues {
panic("debug mode not implemented in explainDebugNode")
}
func (*explainDebugNode) SetLimitHint(_ int64, _ bool) {}