// DecodeIndexKeyPrefix decodes the prefix of an index key and returns the
// index id and a slice for the rest of the key.
//
// Don't use this function in the scan "hot path".
func DecodeIndexKeyPrefix(a *DatumAlloc, desc *TableDescriptor, key []byte) (
indexID IndexID, remaining []byte, err error,
) {
// TODO(dan): This whole operation is n^2 because of the interleaves
// bookkeeping. We could improve it to n with a prefix tree of components.
interleaves := append([]IndexDescriptor{desc.PrimaryIndex}, desc.Indexes...)
for component := 0; ; component++ {
var tableID ID
key, tableID, indexID, err = DecodeTableIDIndexID(key)
if err != nil {
return 0, nil, err
}
if tableID == desc.ID {
// Once desc's table id has been decoded, there can be no more
// interleaves.
remaining = key
break
}
for i := len(interleaves) - 1; i >= 0; i-- {
if len(interleaves[i].Interleave.Ancestors) <= component ||
interleaves[i].Interleave.Ancestors[component].TableID != tableID ||
interleaves[i].Interleave.Ancestors[component].IndexID != indexID {
// This component, and thus this interleave, doesn't match what was
// decoded, remove it.
copy(interleaves[i:], interleaves[i+1:])
interleaves = interleaves[:len(interleaves)-1]
}
}
// The decoded key doesn't many any known interleaves
if len(interleaves) == 0 {
return 0, nil, errors.Errorf("no known interleaves for key")
}
// Anything left has the same SharedPrefixLen at index `component`, so just
// use the first one.
for i := uint32(0); i < interleaves[0].Interleave.Ancestors[component].SharedPrefixLen; i++ {
l, err := encoding.PeekLength(key)
if err != nil {
return 0, nil, err
}
key = key[l:]
}
// We reuse NotNullDescending as the interleave sentinel, consume it.
var ok bool
key, ok = encoding.DecodeIfNotNull(key)
if !ok {
return 0, nil, errors.Errorf("invalid interleave key")
}
}
return indexID, key, err
}
// SetFromBuffer initializes the EncDatum with an encoding that is possibly
// followed by other data. Similar to SetEncoded, except that this function
// figures out where the encoding stops and returns a slice for the rest of the
// buffer.
func (ed *EncDatum) SetFromBuffer(
typ ColumnType_Kind, enc DatumEncoding, buf []byte,
) (remaining []byte, err error) {
var encLen int
switch enc {
case DatumEncoding_ASCENDING_KEY, DatumEncoding_DESCENDING_KEY:
encLen, err = encoding.PeekLength(buf)
case DatumEncoding_VALUE:
encLen, err = roachpb.PeekValueLength(buf)
default:
panic(fmt.Sprintf("unknown encoding %s", ed.encoding))
}
if err != nil {
return nil, err
}
ed.SetEncoded(typ, enc, buf[:encLen])
return buf[encLen:], nil
}