emitter.go
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package influxql
import (
"fmt"
"time"
"github.com/influxdata/influxdb/models"
)
// Emitter groups values together by name, tags, and time.
type Emitter struct {
buf []Point
itrs []Iterator
ascending bool
chunkSize int
tags Tags
row *models.Row
// The columns to attach to each row.
Columns []string
// The time zone location.
Location *time.Location
// Removes the "time" column from output.
// Used for meta queries where time does not apply.
OmitTime bool
}
// NewEmitter returns a new instance of Emitter that pulls from itrs.
func NewEmitter(itrs []Iterator, ascending bool, chunkSize int) *Emitter {
return &Emitter{
buf: make([]Point, len(itrs)),
itrs: itrs,
ascending: ascending,
chunkSize: chunkSize,
Location: time.UTC,
}
}
// Close closes the underlying iterators.
func (e *Emitter) Close() error {
return Iterators(e.itrs).Close()
}
// Emit returns the next row from the iterators.
func (e *Emitter) Emit() (*models.Row, bool, error) {
// Immediately end emission if there are no iterators.
if len(e.itrs) == 0 {
return nil, false, nil
}
// Continually read from iterators until they are exhausted.
for {
// Fill buffer. Return row if no more points remain.
t, name, tags, err := e.loadBuf()
if err != nil {
return nil, false, err
} else if t == ZeroTime {
row := e.row
e.row = nil
return row, false, nil
}
// Read next set of values from all iterators at a given time/name/tags.
// If no values are returned then return row.
values := e.readAt(t, name, tags)
if values == nil {
row := e.row
e.row = nil
return row, false, nil
}
// If there's no row yet then create one.
// If the name and tags match the existing row, append to that row if
// the number of values doesn't exceed the chunk size.
// Otherwise return existing row and add values to next emitted row.
if e.row == nil {
e.createRow(name, tags, values)
} else if e.row.Name == name && e.tags.Equals(&tags) {
if e.chunkSize > 0 && len(e.row.Values) >= e.chunkSize {
row := e.row
row.Partial = true
e.createRow(name, tags, values)
return row, true, nil
}
e.row.Values = append(e.row.Values, values)
} else {
row := e.row
e.createRow(name, tags, values)
return row, true, nil
}
}
}
// loadBuf reads in points into empty buffer slots.
// Returns the next time/name/tags to emit for.
func (e *Emitter) loadBuf() (t int64, name string, tags Tags, err error) {
t = ZeroTime
for i := range e.itrs {
// Load buffer, if empty.
if e.buf[i] == nil {
e.buf[i], err = e.readIterator(e.itrs[i])
if err != nil {
break
}
}
// Skip if buffer is empty.
p := e.buf[i]
if p == nil {
continue
}
itrTime, itrName, itrTags := p.time(), p.name(), p.tags()
// Initialize range values if not set.
if t == ZeroTime {
t, name, tags = itrTime, itrName, itrTags
continue
}
// Update range values if lower and emitter is in time ascending order.
if e.ascending {
if (itrName < name) || (itrName == name && itrTags.ID() < tags.ID()) || (itrName == name && itrTags.ID() == tags.ID() && itrTime < t) {
t, name, tags = itrTime, itrName, itrTags
}
continue
}
// Update range values if higher and emitter is in time descending order.
if (itrName > name) || (itrName == name && itrTags.ID() > tags.ID()) || (itrName == name && itrTags.ID() == tags.ID() && itrTime > t) {
t, name, tags = itrTime, itrName, itrTags
}
}
return
}
// createRow creates a new row attached to the emitter.
func (e *Emitter) createRow(name string, tags Tags, values []interface{}) {
e.tags = tags
e.row = &models.Row{
Name: name,
Tags: tags.KeyValues(),
Columns: e.Columns,
Values: [][]interface{}{values},
}
}
// readAt returns the next slice of values from the iterators at time/name/tags.
// Returns nil values once the iterators are exhausted.
func (e *Emitter) readAt(t int64, name string, tags Tags) []interface{} {
offset := 1
if e.OmitTime {
offset = 0
}
values := make([]interface{}, len(e.itrs)+offset)
if !e.OmitTime {
values[0] = time.Unix(0, t).In(e.Location)
}
e.readInto(t, name, tags, values[offset:])
return values
}
func (e *Emitter) readInto(t int64, name string, tags Tags, values []interface{}) {
for i, p := range e.buf {
// Skip if buffer is empty.
if p == nil {
values[i] = nil
continue
}
// Skip point if it doesn't match time/name/tags.
pTags := p.tags()
if p.time() != t || p.name() != name || !pTags.Equals(&tags) {
values[i] = nil
continue
}
// Read point value.
values[i] = p.value()
// Clear buffer.
e.buf[i] = nil
}
}
// readIterator reads the next point from itr.
func (e *Emitter) readIterator(itr Iterator) (Point, error) {
if itr == nil {
return nil, nil
}
switch itr := itr.(type) {
case FloatIterator:
if p, err := itr.Next(); err != nil {
return nil, err
} else if p != nil {
return p, nil
}
case IntegerIterator:
if p, err := itr.Next(); err != nil {
return nil, err
} else if p != nil {
return p, nil
}
case StringIterator:
if p, err := itr.Next(); err != nil {
return nil, err
} else if p != nil {
return p, nil
}
case BooleanIterator:
if p, err := itr.Next(); err != nil {
return nil, err
} else if p != nil {
return p, nil
}
default:
panic(fmt.Sprintf("unsupported iterator: %T", itr))
}
return nil, nil
}