Github user gparai commented on a diff in the pull request:
https://github.com/apache/drill/pull/729#discussion_r103365674
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/ExecConstants.java ---
@@ -390,4 +391,15 @@
String DYNAMIC_UDF_SUPPORT_ENABLED = "exec.udf.enable_dynamic_support";
BooleanValidator DYNAMIC_UDF_SUPPORT_ENABLED_VALIDATOR = new
BooleanValidator(DYNAMIC_UDF_SUPPORT_ENABLED, true, true);
+
+ /**
+ * Option whose value is a long value representing the number of bits
required for computing ndv (using HLL)
+ */
+ LongValidator NDV_MEMORY_LIMIT = new
PositiveLongValidator("exec.statistics.ndv_memory_limit", 30, 20);
+
+ /**
+ * Option whose value represents the current version of the statistics.
Decreasing the value will generate
+ * the older version of statistics
+ */
+ LongValidator STATISTICS_VERSION = new
NonNegativeLongValidator("exec.statistics.capability_version", 1, 1);
--- End diff --
Say in the next version(v2), we add histograms. Computing stats is
expensive so users might prefer to remain on the present version(v1) maybe
because their queries do not involve too many inequalities. Always generating
the latest version of the stats will force the users to compute the latest and
greatest stats without needing them. On the other hand, providing individual
control of which statistic to compute moves too much burden onto the user to
figure out exactly which statistics would help their use-cases.
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