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trace.go
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trace.go
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// Copyright 2016 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: Tobias Schottdorf (tobias.schottdorf@gmail.com)
package sql
import (
"fmt"
"time"
basictracer "github.com/opentracing/basictracer-go"
opentracing "github.com/opentracing/opentracing-go"
otlog "github.com/opentracing/opentracing-go/log"
"golang.org/x/net/context"
"github.com/cockroachdb/cockroach/pkg/roachpb"
"github.com/cockroachdb/cockroach/pkg/sql/parser"
"github.com/cockroachdb/cockroach/pkg/sql/sqlbase"
"github.com/cockroachdb/cockroach/pkg/util/encoding"
"github.com/cockroachdb/cockroach/pkg/util/tracing"
)
// explainTraceNode 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 (TRACE) statements.
type explainTraceNode struct {
plan planNode
// Internal state, not to be initialized.
earliest time.Time
exhausted bool
rows []parser.Datums
lastTS time.Time
lastPos int
trace *tracing.RecordedTrace
p *planner
// Initialized at Start() time. When called, restores the planner's context to
// what it was before this node hijacked it.
restorePlannerCtx func()
tracingCtx context.Context
}
var traceColumns = append(sqlbase.ResultColumns{
{Name: "Cumulative Time", Typ: parser.TypeString},
{Name: "Duration", Typ: parser.TypeString},
{Name: "Span Pos", Typ: parser.TypeInt},
{Name: "Operation", Typ: parser.TypeString},
{Name: "Event", Typ: parser.TypeString},
}, debugColumns...)
// Internally, the explainTraceNode also returns a timestamp column which is
// used during sorting.
var traceColumnsWithTS = append(traceColumns, sqlbase.ResultColumn{
Name: "Timestamp", Typ: parser.TypeTimestamp,
})
var traceOrdering = sqlbase.ColumnOrdering{
{ColIdx: len(traceColumns), Direction: encoding.Ascending}, /* Start time */
{ColIdx: 2, Direction: encoding.Ascending}, /* Span pos */
}
func (p *planner) makeTraceNode(plan planNode) planNode {
return &sortNode{
plan: &explainTraceNode{
plan: plan,
p: p,
},
p: p,
ordering: traceOrdering,
// These are the columns that the sortNode (and thus the selectTopNode)
// presents as the output.
columns: traceColumns,
}
}
func (n *explainTraceNode) Start(ctx context.Context) error {
return n.plan.Start(ctx)
}
// hijackTxnContext hijacks the session's/txn's context, causing everything
// happening in the current txn before explainTraceNode.Close() to happen inside
// a recorded trace.
//
// TODO(andrei): This is currently called from Next(), which means that
// `n.plan.Start()` is not traced. That's a shame, but unfortunately we can't
// hijack in explainTraceNode.Start() because we need to only hijack after the
// sortNode wrapping the explainTraceNode has started execution. This is because
// the context that's passed to the first call of sortNode.Next() (the call
// that's responsible for exhausting the explainTraceNode) needs to be the
// un-hijacked one - otherwise, the hijacked ctx will be used by that call to
// sortNode.Next() after the explandPlanNode closes the tracing span (resulting
// in a span use-after-finish).
func (n *explainTraceNode) hijackTxnContext(ctx context.Context) error {
tracingCtx, recorder, err := tracing.StartSnowballTrace(ctx, "explain trace")
if err != nil {
return err
}
n.trace = recorder
n.tracingCtx = tracingCtx
// Everything running on the planner/session until Close() will be done with
// the tracingCtx. More exactly, the inner n.plan will run with this hijacked
// context.
n.restorePlannerCtx = n.p.session.hijackCtx(tracingCtx)
return nil
}
func (n *explainTraceNode) Close(ctx context.Context) {
if n.restorePlannerCtx != nil {
n.unhijackCtx()
sp := opentracing.SpanFromContext(n.tracingCtx)
sp.Finish()
}
n.plan.Close(ctx)
}
func (n *explainTraceNode) unhijackCtx() {
// Restore the hijacked context on the planner.
n.restorePlannerCtx()
n.restorePlannerCtx = nil
}
func (n *explainTraceNode) Next(ctx context.Context) (bool, error) {
first := n.rows == nil
if first {
n.rows = []parser.Datums{}
if err := n.hijackTxnContext(ctx); err != nil {
return false, err
}
// After the call to hijackTxnContext, the current and future invocations of
// explainTraceNode.Next() need to use n.tracingCtx instead of the method
// argument.
}
for !n.exhausted && len(n.rows) <= 1 {
var vals debugValues
if next, err := n.plan.Next(n.tracingCtx); !next {
sp := opentracing.SpanFromContext(n.tracingCtx)
n.exhausted = true
// Finish the tracing span that we began in Start().
if err != nil {
sp.LogFields(otlog.String("event", err.Error()))
return false, err
}
sp.LogFields(otlog.String("event", "tracing completed"))
n.unhijackCtx()
sp.Finish()
} else {
vals = n.plan.DebugValues()
}
var basePos int
if len(n.trace.GetSpans()) == 0 {
if !n.exhausted {
n.trace.AddDummySpan(basictracer.RawSpan{
Logs: []opentracing.LogRecord{{Timestamp: n.lastTS}},
})
}
basePos = n.lastPos + 1
}
// Iterate through once to determine earliest timestamp.
var earliest time.Time
for _, sp := range n.trace.GetSpans() {
for _, entry := range sp.Logs {
if n.earliest.IsZero() || entry.Timestamp.Before(earliest) {
n.earliest = entry.Timestamp
}
}
}
for _, sp := range n.trace.GetSpans() {
for i, entry := range sp.Logs {
commulativeDuration := fmt.Sprintf("%.3fms", entry.Timestamp.Sub(n.earliest).Seconds()*1000)
var duration string
if i > 0 {
duration = fmt.Sprintf("%.3fms", entry.Timestamp.Sub(n.lastTS).Seconds()*1000)
}
// Extract the message of the event, which is either in an "event" or
// "error" field.
var msg string
for _, f := range entry.Fields {
key := f.Key()
if key == "event" {
msg = fmt.Sprint(f.Value())
break
}
if key == "error" {
msg = fmt.Sprint("error:", f.Value())
break
}
}
cols := append(parser.Datums{
parser.NewDString(commulativeDuration),
parser.NewDString(duration),
parser.NewDInt(parser.DInt(basePos + i)),
parser.NewDString(sp.Operation),
parser.NewDString(msg),
}, vals.AsRow()...)
// Timestamp is added for sorting, but will be removed after sort.
n.rows = append(n.rows, append(cols, parser.MakeDTimestamp(entry.Timestamp, time.Nanosecond)))
n.lastTS, n.lastPos = entry.Timestamp, i
}
}
// Clear the spans that have been accumulated so far, so that we'll
// associate new spans with the next "debug values".
n.trace.ClearSpans()
}
if first {
return len(n.rows) > 0, nil
}
if len(n.rows) <= 1 {
return false, nil
}
n.rows = n.rows[1:]
return true, nil
}
func (n *explainTraceNode) Values() parser.Datums {
return n.rows[0]
}
func (*explainTraceNode) Columns() sqlbase.ResultColumns { return traceColumnsWithTS }
func (*explainTraceNode) Ordering() orderingInfo { return orderingInfo{} }
func (*explainTraceNode) MarkDebug(_ explainMode) {}
func (*explainTraceNode) DebugValues() debugValues { return debugValues{} }
func (n *explainTraceNode) Spans(ctx context.Context) (_, _ roachpb.Spans, _ error) {
return n.plan.Spans(ctx)
}