Package org.apache.druid.query

Interface DataSource

All Superinterfaces:
Cacheable
All Known Implementing Classes:
FilteredDataSource, FrameBasedInlineDataSource, GlobalTableDataSource, InlineDataSource, JoinDataSource, LeafDataSource, LookupDataSource, QueryDataSource, RestrictedDataSource, TableDataSource, UnionDataSource, UnnestDataSource
public interface DataSource extends Cacheable
Represents a source... of data... for a query. Analogous to the "FROM" clause in SQL.

  • Field Details

  • Method Details

    • getTableNames

      Set<String> getTableNames()
      Returns the names of all table datasources involved in this query. Does not include names for non-tables, like lookups or inline datasources.

    • getChildren

      List<DataSource> getChildren()
      Returns datasources that this datasource depends on. Will be empty for leaf datasources like 'table'.

    • withChildren

      DataSource withChildren(List<DataSource> children)
      Return a new DataSource, identical to this one, with different children. The number of children must be equal to the number of children that this datasource already has.

    • isCacheable

      boolean isCacheable(boolean isBroker)
      Returns true if queries on this dataSource are cacheable at both the result level and per-segment level. Currently, dataSources that do not actually reference segments (like 'inline'), are not cacheable since cache keys are always based on segment identifiers.

    • isGlobal

      boolean isGlobal()
      Decides if this datasource can be accessed globally.

      This means that all servers have a full copy of this datasource.

      Examples: inline table, lookup.

    • isProcessable

      boolean isProcessable()
      Communicates that this DataSource can be directly used to run a Query.

      A Processable datasource must pack the necessary logic into the createSegmentMapFunction(Query).

      Processable examples are: TableDataSource, InlineDataSource, FilteredDataSource. Non-processable ones are those which need further pre-processing before running them. examples are: QueryDataSource and join which are not supported directly.

    • createSegmentMapFunction

      SegmentMapFunction createSegmentMapFunction(Query query)
      Returns a segment function on to how to segment should be modified.

    • createSegmentPruner

      @Nullable default SegmentPruner createSegmentPruner()
      Returns a SegmentPruner if this datasource embeds in any information which can be used to determine if a segment needs processed or not. Note that callers of this method will always only be processing segments for the datasource, so there is no need for a 'default' pruner that ensures the segment has the proper datasource. A return value of null indicates that no pruning can be performed from this datasource, though other sources of pruning, such as filters may still be used.

    • withPolicies

      default DataSource withPolicies(Map<String,Optional<Policy>> policyMap, PolicyEnforcer policyEnforcer)
      Returns an updated datasource based on the policy restrictions on tables.

      If this datasource contains no table, no changes should occur.

      Parameters:
      policyMap - a mapping of table names to policy restrictions. A missing key is different from an empty value:
      • a missing key means the table has never been permission checked.
      • an empty value indicates the table doesn't have any policy restrictions, it has been permission checked.
      policyEnforcer - the policy enforcer to enforce the result datasource complies
      Returns:
      the updated datasource, with restrictions applied in the datasource tree
      Throws:
      IllegalStateException - when mapping a RestrictedDataSource, unless the table has a NoRestrictionPolicy in the policyMap (used by druid-internal). Missing policy or adding a non-NoRestrictionPolicy to RestrictedDataSource would throw.

    • getCacheKey

      @Nullable byte[] getCacheKey()
      Compute a cache key prefix for a data source. This includes the data sources that participate in the RHS of a join as well as any query specific constructs associated with join data source such as base table filter. This key prefix can be used in segment level cache or result level cache. The function can return following - Non-empty byte array - If there is join datasource involved and caching is possible. The result includes join condition expression, join type and cache key returned by joinable factory for each PreJoinableClause - NULL - There is a join but caching is not possible. It may happen if one of the participating datasource in the JOIN is not cacheable.
      Specified by:
      getCacheKey in interface Cacheable
      Returns:
      the cache key to be used as part of query cache key