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encoded_datum.go
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encoded_datum.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: Radu Berinde (radu@cockroachlabs.com)
package sqlbase
import (
"bytes"
"fmt"
"github.com/cockroachdb/cockroach/pkg/sql/parser"
"github.com/cockroachdb/cockroach/pkg/util/encoding"
"github.com/pkg/errors"
)
// EncDatum represents a datum that is "backed" by an encoding and/or by a
// parser.Datum. It allows "passing through" a Datum without decoding and
// reencoding.
type EncDatum struct {
Type ColumnType
// Encoding type. Valid only if encoded is not nil.
encoding DatumEncoding
// Encoded datum (according to the encoding field).
encoded []byte
// Decoded datum.
Datum parser.Datum
}
func (ed *EncDatum) stringWithAlloc(a *DatumAlloc) string {
if ed.Datum == nil {
if ed.encoded == nil {
return "<unset>"
}
if a == nil {
a = &DatumAlloc{}
}
err := ed.EnsureDecoded(a)
if err != nil {
return fmt.Sprintf("<error: %v>", err)
}
}
return ed.Datum.String()
}
func (ed *EncDatum) String() string {
return ed.stringWithAlloc(nil)
}
// EncDatumFromEncoded initializes an EncDatum with the given encoded
// value. The encoded value is stored as a shallow copy, so the caller must
// make sure the slice is not modified for the lifetime of the EncDatum.
// SetEncoded wipes the underlying Datum.
func EncDatumFromEncoded(typ ColumnType, enc DatumEncoding, encoded []byte) EncDatum {
if len(encoded) == 0 {
panic("empty encoded value")
}
return EncDatum{
Type: typ,
encoding: enc,
encoded: encoded,
Datum: nil,
}
}
// EncDatumFromBuffer initializes an EncDatum with an encoding that is
// possibly followed by other data. Similar to EncDatumFromEncoded,
// except that this function figures out where the encoding stops and returns a
// slice for the rest of the buffer.
func EncDatumFromBuffer(typ ColumnType, enc DatumEncoding, buf []byte) (EncDatum, []byte, error) {
switch enc {
case DatumEncoding_ASCENDING_KEY, DatumEncoding_DESCENDING_KEY:
encLen, err := encoding.PeekLength(buf)
if err != nil {
return EncDatum{}, nil, err
}
ed := EncDatumFromEncoded(typ, enc, buf[:encLen])
return ed, buf[encLen:], nil
case DatumEncoding_VALUE:
typeOffset, encLen, err := encoding.PeekValueLength(buf)
if err != nil {
return EncDatum{}, nil, err
}
ed := EncDatumFromEncoded(typ, enc, buf[typeOffset:encLen])
return ed, buf[encLen:], nil
default:
panic(fmt.Sprintf("unknown encoding %s", enc))
}
}
// DatumToEncDatum initializes an EncDatum with the given Datum.
func DatumToEncDatum(ctyp ColumnType, d parser.Datum) EncDatum {
if d == nil {
panic("Cannot convert nil datum to EncDatum")
}
if ptyp := ctyp.ToDatumType(); d != parser.DNull && !ptyp.Equivalent(d.ResolvedType()) {
panic(fmt.Sprintf("invalid datum type given: %s, expected %s",
d.ResolvedType(), ptyp))
}
return EncDatum{
Type: ctyp,
Datum: d,
}
}
// UnsetDatum ensures subsequent IsUnset() calls return false.
func (ed *EncDatum) UnsetDatum() {
ed.encoded = nil
ed.Datum = nil
ed.encoding = 0
}
// IsUnset returns true if SetEncoded or SetDatum were not called.
func (ed *EncDatum) IsUnset() bool {
return ed.encoded == nil && ed.Datum == nil
}
// IsNull returns true if the EncDatum value is NULL. Equivalent to checking if
// ed.Datum is DNull after calling EnsureDecoded.
func (ed *EncDatum) IsNull() bool {
if ed.Datum != nil {
return ed.Datum == parser.DNull
}
if ed.encoded == nil {
panic("IsNull on unset EncDatum")
}
switch ed.encoding {
case DatumEncoding_ASCENDING_KEY, DatumEncoding_DESCENDING_KEY:
_, isNull := encoding.DecodeIfNull(ed.encoded)
return isNull
case DatumEncoding_VALUE:
_, _, _, typ, err := encoding.DecodeValueTag(ed.encoded)
if err != nil {
panic(err)
}
return typ == encoding.Null
default:
panic(fmt.Sprintf("unknown encoding %s", ed.encoding))
}
}
// EnsureDecoded ensures that the Datum field is set (decoding if it is not).
func (ed *EncDatum) EnsureDecoded(a *DatumAlloc) error {
if ed.Datum != nil {
return nil
}
if ed.encoded == nil {
panic("decoding unset EncDatum")
}
datType := ed.Type.ToDatumType()
var err error
var rem []byte
switch ed.encoding {
case DatumEncoding_ASCENDING_KEY:
ed.Datum, rem, err = DecodeTableKey(a, datType, ed.encoded, encoding.Ascending)
case DatumEncoding_DESCENDING_KEY:
ed.Datum, rem, err = DecodeTableKey(a, datType, ed.encoded, encoding.Descending)
case DatumEncoding_VALUE:
ed.Datum, rem, err = DecodeTableValue(a, datType, ed.encoded)
default:
panic(fmt.Sprintf("unknown encoding %s", ed.encoding))
}
if err != nil {
return err
}
if len(rem) != 0 {
ed.Datum = nil
return errors.Errorf("%d trailing bytes in encoded value", len(rem))
}
return nil
}
// Encoding returns the encoding that is already available (the latter indicated
// by the bool return value).
func (ed *EncDatum) Encoding() (DatumEncoding, bool) {
if ed.encoded == nil {
return 0, false
}
return ed.encoding, true
}
// Encode appends the encoded datum to the given slice using the requested
// encoding.
// Note: DatumEncoding_VALUE encodings are not unique because they can contain
// a column ID so they should not be used to test for equality.
func (ed *EncDatum) Encode(a *DatumAlloc, enc DatumEncoding, appendTo []byte) ([]byte, error) {
if ed.encoded != nil && enc == ed.encoding {
// We already have an encoding that matches
return append(appendTo, ed.encoded...), nil
}
if err := ed.EnsureDecoded(a); err != nil {
return nil, err
}
switch enc {
case DatumEncoding_ASCENDING_KEY:
return EncodeTableKey(appendTo, ed.Datum, encoding.Ascending)
case DatumEncoding_DESCENDING_KEY:
return EncodeTableKey(appendTo, ed.Datum, encoding.Descending)
case DatumEncoding_VALUE:
return EncodeTableValue(appendTo, ColumnID(encoding.NoColumnID), ed.Datum)
default:
panic(fmt.Sprintf("unknown encoding requested %s", enc))
}
}
// Compare returns:
// -1 if the receiver is less than rhs,
// 0 if the receiver is equal to rhs,
// +1 if the receiver is greater than rhs.
func (ed *EncDatum) Compare(
a *DatumAlloc, evalCtx *parser.EvalContext, rhs *EncDatum,
) (int, error) {
// TODO(radu): if we have both the Datum and a key encoding available, which
// one would be faster to use?
if ed.encoding == rhs.encoding && ed.encoded != nil && rhs.encoded != nil {
switch ed.encoding {
case DatumEncoding_ASCENDING_KEY:
return bytes.Compare(ed.encoded, rhs.encoded), nil
case DatumEncoding_DESCENDING_KEY:
return bytes.Compare(rhs.encoded, ed.encoded), nil
}
}
if err := ed.EnsureDecoded(a); err != nil {
return 0, err
}
if err := rhs.EnsureDecoded(a); err != nil {
return 0, err
}
return ed.Datum.Compare(evalCtx, rhs.Datum), nil
}
// EncDatumRow is a row of EncDatums.
type EncDatumRow []EncDatum
func (r EncDatumRow) stringToBuf(a *DatumAlloc, b *bytes.Buffer) {
b.WriteString("[")
for i := range r {
if i > 0 {
b.WriteString(" ")
}
b.WriteString(r[i].stringWithAlloc(a))
}
b.WriteString("]")
}
func (r EncDatumRow) String() string {
var b bytes.Buffer
r.stringToBuf(&DatumAlloc{}, &b)
return b.String()
}
// EncDatumRowToDatums converts a given EncDatumRow to a Datums.
func EncDatumRowToDatums(datums parser.Datums, row EncDatumRow, da *DatumAlloc) error {
if len(row) != len(datums) {
return errors.Errorf(
"Length mismatch (%d and %d) between datums and row", len(datums), len(row))
}
for i, encDatum := range row {
if encDatum.IsUnset() {
datums[i] = parser.DNull
continue
}
err := encDatum.EnsureDecoded(da)
if err != nil {
return err
}
datums[i] = encDatum.Datum
}
return nil
}
// Compare returns the relative ordering of two EncDatumRows according to a
// ColumnOrdering:
// -1 if the receiver comes before the rhs in the ordering,
// +1 if the receiver comes after the rhs in the ordering,
// 0 if the relative order does not matter (i.e. the two rows have the same
// values for the columns in the ordering).
//
// Note that a return value of 0 does not (in general) imply that the rows are
// equal; for example, rows [1 1 5] and [1 1 6] when compared against ordering
// {{0, asc}, {1, asc}} (i.e. ordered by first column and then by second
// column).
func (r EncDatumRow) Compare(
a *DatumAlloc, ordering ColumnOrdering, evalCtx *parser.EvalContext, rhs EncDatumRow,
) (int, error) {
for _, c := range ordering {
cmp, err := r[c.ColIdx].Compare(a, evalCtx, &rhs[c.ColIdx])
if err != nil {
return 0, err
}
if cmp != 0 {
if c.Direction == encoding.Descending {
cmp = -cmp
}
return cmp, nil
}
}
return 0, nil
}
// CompareToDatums is a version of Compare which compares against decoded Datums.
func (r EncDatumRow) CompareToDatums(
a *DatumAlloc, ordering ColumnOrdering, evalCtx *parser.EvalContext, rhs parser.Datums,
) (int, error) {
for _, c := range ordering {
if err := r[c.ColIdx].EnsureDecoded(a); err != nil {
return 0, err
}
cmp := r[c.ColIdx].Datum.Compare(evalCtx, rhs[c.ColIdx])
if cmp != 0 {
if c.Direction == encoding.Descending {
cmp = -cmp
}
return cmp, nil
}
}
return 0, nil
}
// EncDatumRows is a slice of EncDatumRows.
type EncDatumRows []EncDatumRow
func (r EncDatumRows) String() string {
var a DatumAlloc
var b bytes.Buffer
b.WriteString("[")
for i, r := range r {
if i > 0 {
b.WriteString(" ")
}
r.stringToBuf(&a, &b)
}
b.WriteString("]")
return b.String()
}
// EncDatumRowAlloc is a helper that speeds up allocation of EncDatumRows
// (preferably of the same length).
type EncDatumRowAlloc struct {
buf []EncDatum
// Preallocate a small initial batch (helps cases where
// we only allocate a few small rows).
prealloc [16]EncDatum
}
// AllocRow allocates an EncDatumRow with the given number of columns.
func (a *EncDatumRowAlloc) AllocRow(cols int) EncDatumRow {
if a.buf == nil {
// First call.
a.buf = a.prealloc[:]
}
if len(a.buf) < cols {
// If the rows are small, allocate storage for a bunch of rows at once.
bufLen := cols
if cols <= 16 {
bufLen *= 16
} else if cols <= 64 {
bufLen *= 4
}
a.buf = make([]EncDatum, bufLen)
}
// Chop off a row from buf, and limit its capacity to avoid corrupting the
// following row in the unlikely case that the caller appends to the slice.
result := EncDatumRow(a.buf[:cols:cols])
a.buf = a.buf[cols:]
return result
}
// CopyRow allocates an EncDatumRow and copies the given row to it.
func (a *EncDatumRowAlloc) CopyRow(row EncDatumRow) EncDatumRow {
rowCopy := a.AllocRow(len(row))
copy(rowCopy, row)
return rowCopy
}