// maybeAddDefinition possibly adds a new IndexDefinitionSortable to this slice.
// It's only added if it could be useful in servicing q, otherwise this function
// is a noop.
//
// This returns true iff the proposed index is OK and depletes missingTerms to
// empty.
//
// If the proposed index is PERFECT (e.g. contains enough columns to cover all
// equality filters, and also has the correct suffix), idxs will be replaced
// with JUST that index, and this will return true.
func (idxs *IndexDefinitionSortableSlice) maybeAddDefinition(q *reducedQuery, s *memStore, missingTerms stringSet, id *ds.IndexDefinition) bool {
// Kindless queries are handled elsewhere.
if id.Kind != q.kind {
impossible(
fmt.Errorf("maybeAddDefinition given index with wrong kind %q v %q", id.Kind, q.kind))
}
// If we're an ancestor query, and the index is compound, but doesn't include
// an Ancestor field, it doesn't work. Builtin indexes can be used for
// ancestor queries (and have !Ancestor), assuming that it's only equality
// filters (plus inequality on __key__), or a single inequality.
if q.eqFilters["__ancestor__"] != nil && !id.Ancestor && !id.Builtin() {
impossible(
fmt.Errorf("maybeAddDefinition given compound index with wrong ancestor info: %s %#v", id, q))
}
// add __ancestor__ if necessary
sortBy := id.GetFullSortOrder()
// If the index has fewer fields than we need for the suffix, it can't
// possibly help.
if len(sortBy) < len(q.suffixFormat) {
return false
}
numEqFilts := len(sortBy) - len(q.suffixFormat)
// make sure the orders are precisely the same
for i, sb := range sortBy[numEqFilts:] {
if q.suffixFormat[i] != sb {
return false
}
}
if id.Builtin() && numEqFilts == 0 {
if len(q.eqFilters) > 1 || (len(q.eqFilters) == 1 && q.eqFilters["__ancestor__"] == nil) {
return false
}
}
// Make sure the equalities section doesn't contain any properties we don't
// want in our query.
//
// numByProp && totalEqFilts will be used to see if this is a perfect match
// later.
numByProp := make(map[string]int, len(q.eqFilters))
totalEqFilts := 0
eqFilts := sortBy[:numEqFilts]
for _, p := range eqFilts {
if _, ok := q.eqFilters[p.Property]; !ok {
return false
}
numByProp[p.Property]++
totalEqFilts++
}
// ok, we can actually use this
// Grab the collection for convenience later. We don't want to invalidate this
// index's potential just because the collection doesn't exist. If it's
// a builtin and it doesn't exist, it still needs to be one of the 'possible'
// indexes... it just means that the user's query will end up with no results.
coll := s.GetCollection(
fmt.Sprintf("idx:%s:%s", q.ns, serialize.ToBytes(*id.PrepForIdxTable())))
// First, see if it's a perfect match. If it is, then our search is over.
//
// A perfect match contains ALL the equality filter columns (or more, since
// we can use residuals to fill in the extras).
toAdd := IndexDefinitionSortable{coll: coll}
toAdd.eqFilts = eqFilts
for _, sb := range toAdd.eqFilts {
missingTerms.rm(sb.Property)
}
perfect := false
if len(sortBy) == q.numCols {
perfect = true
for k, num := range numByProp {
if num < len(q.eqFilters[k]) {
perfect = false
break
}
}
}
if perfect {
*idxs = IndexDefinitionSortableSlice{toAdd}
} else {
*idxs = append(*idxs, toAdd)
}
return len(missingTerms) == 0
}
