Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/536#discussion_r82495511
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/PlannerSettings.java
---
@@ -46,40 +46,83 @@
// max off heap memory for planning (16G)
private static final long MAX_OFF_HEAP_ALLOCATION_IN_BYTES = 16l * 1024
* 1024 * 1024;
- public static final OptionValidator CONSTANT_FOLDING = new
BooleanValidator("planner.enable_constant_folding", true);
+ public static final OptionValidator CONSTANT_FOLDING = new
BooleanValidator("planner.enable_constant_folding", true,
+ "If one side of a filter condition is a constant expression,
constant folding evaluates the expression in the" +
+ " planning phase and replaces the expression with the constant
value. For example, Drill can rewrite" +
+ " this clause ' WHERE age + 5 < 42 as WHERE age < 37'.");
+
public static final OptionValidator EXCHANGE = new
BooleanValidator("planner.disable_exchanges", false);
+
public static final OptionValidator HASHAGG = new
BooleanValidator("planner.enable_hashagg", true);
+
public static final OptionValidator STREAMAGG = new
BooleanValidator("planner.enable_streamagg", true);
- public static final OptionValidator HASHJOIN = new
BooleanValidator("planner.enable_hashjoin", true);
- public static final OptionValidator MERGEJOIN = new
BooleanValidator("planner.enable_mergejoin", true);
+
+ public static final OptionValidator HASHJOIN = new
BooleanValidator("planner.enable_hashjoin", true,
+ "Enable the memory hungry hash join. Drill assumes that a query with
have adequate memory to complete and" +
+ " tries to use the fastest operations possible to complete the
planned inner, left, right, or full outer" +
+ " joins using a hash table. Does not write to disk. Disabling
hash join allows Drill to manage arbitrarily" +
+ " large data in a small memory footprint.");
+
+ public static final OptionValidator MERGEJOIN = new
BooleanValidator("planner.enable_mergejoin", true,
+ "Sort-based operation. A merge join is used for inner join, left and
right outer joins. Inputs to the merge" +
+ " join must be sorted. It reads the sorted input streams from
both sides and finds matching rows." +
+ " Writes to disk.");
+
public static final OptionValidator NESTEDLOOPJOIN = new
BooleanValidator("planner.enable_nestedloopjoin", true);
+
public static final OptionValidator MULTIPHASE = new
BooleanValidator("planner.enable_multiphase_agg", true);
- public static final OptionValidator BROADCAST = new
BooleanValidator("planner.enable_broadcast_join", true);
- public static final OptionValidator BROADCAST_THRESHOLD = new
PositiveLongValidator("planner.broadcast_threshold", MAX_BROADCAST_THRESHOLD,
10000000);
- public static final OptionValidator BROADCAST_FACTOR = new
RangeDoubleValidator("planner.broadcast_factor", 0, Double.MAX_VALUE, 1.0d);
- public static final OptionValidator NESTEDLOOPJOIN_FACTOR = new
RangeDoubleValidator("planner.nestedloopjoin_factor", 0, Double.MAX_VALUE,
100.0d);
- public static final OptionValidator NLJOIN_FOR_SCALAR = new
BooleanValidator("planner.enable_nljoin_for_scalar_only", true);
- public static final OptionValidator JOIN_ROW_COUNT_ESTIMATE_FACTOR = new
RangeDoubleValidator("planner.join.row_count_estimate_factor", 0,
Double.MAX_VALUE, 1.0d);
+
+ public static final OptionValidator BROADCAST = new
BooleanValidator("planner.enable_broadcast_join", true,
+ "The broadcast join can be used for hash join, merge join and nested
loop join. Use to join a large (fact)" +
+ " table to relatively smaller (dimension) tables. This should be
enabled.");
+ public static final OptionValidator BROADCAST_THRESHOLD = new
PositiveLongValidator("planner.broadcast_threshold",
+ MAX_BROADCAST_THRESHOLD, 10000000, "The maximum number of records
allowed to be broadcast as part of a query." +
+ " If the threshold is exceeded, Drill reshuffles data rather than
doing a broadcast to one side of the" +
+ " join. Range: 0 - " + MAX_BROADCAST_THRESHOLD + ".");
+ public static final OptionValidator BROADCAST_FACTOR = new
RangeDoubleValidator("planner.broadcast_factor", 0,
+ Double.MAX_VALUE, 1.0d, "A heuristic parameter for influencing the
broadcast of records as part of a query.");
--- End diff --
Increasing the value does... what?
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