Package com.apple.foundationdb.record

Interface QueryHashable

All Known Subinterfaces:

AtomKeyExpression, Comparisons.Comparison, ComponentWithChildren, ComponentWithComparison, ComponentWithNoChildren, ComponentWithSingleChild, IndexQueryabilityFilter, KeyExpression, KeyExpressionWithChild, KeyExpressionWithChildren, KeyExpressionWithoutChildren, KeyExpressionWithValue, QueryableKeyExpression, QueryComponent

All Known Implementing Classes:

AndComponent, AndOrComponent, BaseField, BaseKeyExpression, BaseNestedField, CollateFunctionKeyExpression, CollateFunctionKeyExpressionFactoryJRE.CollateFunctionKeyExpressionJRE, Comparisons.ListComparison, Comparisons.MultiColumnComparison, Comparisons.NullComparison, Comparisons.ParameterComparison, Comparisons.SimpleComparison, Comparisons.TextComparison, Comparisons.TextContainsAllPrefixesComparison, Comparisons.TextWithMaxDistanceComparison, EmptyComparison, EmptyKeyExpression, FieldKeyExpression, FieldWithComparison, FunctionKeyExpression, GroupingKeyExpression, IndexRecordFunction, KeyWithValueExpression, ListKeyExpression, LiteralKeyExpression, NestedField, NestingKeyExpression, NotComponent, ObjectPlanHash, OneOfThemWithComparison, OneOfThemWithComponent, OrComponent, QueryKeyExpressionWithComparison, QueryRecordFunctionWithComparison, RecordFunction, RecordQuery, RecordTypeKeyComparison, RecordTypeKeyExpression, SplitKeyExpression, StoreRecordFunction, ThenKeyExpression, TimeWindowRecordFunction, VersionKeyExpression

public interface QueryHashable

Query hash - calculate and return identifying hash values for queries. The queryHash semantics are different than Object.hashCode() in a few ways:

• queryHash(com.apple.foundationdb.record.QueryHashable.QueryHashKind) values should be stable across runtime instance changes. The reason is that these values are going to be used to correlate queries with plans across multiple instances, and so need to be repeatable and stable.
• queryHash(com.apple.foundationdb.record.QueryHashable.QueryHashKind) supports multiple flavors of hash calculations (See QueryHashable.QueryHashKind). The various kinds of hash values are used for different purposes and include/exclude different parts of the target query
• queryHash(com.apple.foundationdb.record.QueryHashable.QueryHashKind) is meant to imply a certain identity of a query, and reflects on the entire structure of the query. The intent is to be able to correlate various queries for "identity" (using different definitions for this identity as specified by QueryHashable.QueryHashKind). This requirement drives a desire to reduce collisions as much as possible since not in all cases can we actually use "equals" to verify identity (e.g. log messages)

See also PlanHashable

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static class	QueryHashable.QueryHashKind	The "kinds" of queryHash calculations.

Method Summary

Modifier and Type	Method	Description
int	queryHash(QueryHashable.QueryHashKind hashKind)	Return a hash similar to hashCode, but with the additional guarantee that is is stable across JVMs.

Method Detail

queryHash

int queryHash(@Nonnull
              QueryHashable.QueryHashKind hashKind)

Return a hash similar to hashCode, but with the additional guarantee that is is stable across JVMs.

Parameters:

hashKind - the "kind" of hash to calculate. Each kind of hash has a particular logic with regards to included and excluded items.

Returns:

a stable hash code