Class CrossJoinHelper
public class CrossJoinHelper extends Object
Table.join(com.illumon.iris.db.tables.Table)
(referred to as simply join or "cross join") and a left outer join. The left outer join does not currently have
any user visible API.
When there are zero keys, the result table uses BitShiftingColumnSources for the columns derived from the
left table and a BitMaskingColumnSource for the columns on the right. The index key space has some number
of bits for shifting, the low order bits are directly translated to the right table's index; the high order bits are
shifted to the right and indexed into the left table. For example if the right table has an index of {0, 1, 7}; then
3 bits are required to address the right table and the remainder of the bits are used for the left table.
For a bucketed cross join, the number of RHS bits is determined by the size of the largest group. The LHS sources
are similarly shifted using a BitShiftingColumnSource, but instead of using the index space of the right hand
side directly each group is flattened. The RHS ues a CrossJoinRightColumnSource to handle these flat indices.
So in the case where we had a group containing an index of {0, 1, 7} it only requires 2 bits (for 3 values) not 3 bits
(to represent the key 7). When values are added or removed from the RHS, the remaining values must appropriately
shift to maintain the flat space. If the largest right hand side group increases, then we must increase the number
of bits dedicated to the RHS and all of the groups require a shift.
The difference between a cross join and a left outer join is that in the case there are zero matching RHS rows, the cross join does not produce any output for that state. For the left outer join, a single row with null RHS values is produced. When a tick causes a transition from empty to non-empty or vice-versa the matched row is added or removed and the corresponding null row is removed or added in the downstream update (as opposed to being represented as a modification).
From a user-perspective, when the operation can be suitably performed using a Table.naturalJoin(com.illumon.iris.db.tables.Table, com.illumon.iris.db.tables.select.MatchPair[], com.illumon.iris.db.tables.select.MatchPair[]), that
operation should be preferred. The LHS columns and Index are passed through unchanged in a naturalJoin and the right
columns have a simpler redirection. The simpler naturalJoin is likely to provide better performance, though can not
handle results that require multiple RHS rows.
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Field Summary
Fields Modifier and Type Field Description static intDEFAULT_NUM_RIGHT_BITS_TO_RESERVE -
Method Summary
Modifier and Type Method Description static TableleftOuterJoin(com.fishlib.io.logger.Logger log, QueryTable leftTable, QueryTable rightTable, MatchPair[] columnsToMatch, MatchPair[] columnsToAdd, int numReserveRightBits)
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Field Details
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DEFAULT_NUM_RIGHT_BITS_TO_RESERVE
public static final int DEFAULT_NUM_RIGHT_BITS_TO_RESERVE
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Method Details
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leftOuterJoin
public static Table leftOuterJoin(com.fishlib.io.logger.Logger log, QueryTable leftTable, QueryTable rightTable, MatchPair[] columnsToMatch, MatchPair[] columnsToAdd, int numReserveRightBits)
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