Github user amansinha100 commented on a diff in the pull request:
https://github.com/apache/drill/pull/185#discussion_r40981727
--- Diff:
contrib/storage-hive/core/src/main/java/org/apache/drill/exec/store/hive/HiveScan.java
---
@@ -319,16 +319,12 @@ public ScanStats getScanStats() {
estRowCount = data/1024;
}
- // Hive's native reader is neither memory efficient nor fast. If the
rowcount is below
- // HIVE_SERDE_SCAN_OVERHEAD_FACTOR, make sure it is at least
HIVE_SERDE_SCAN_OVERHEAD_FACTOR to enable the planner
- // to choose HiveDrillNativeParquetScan. Due to the project on top
of HiveDrillNativeParquetScan, we end up
- // choosing the HiveScan instead of HiveDrillNativeParquetScan if
the cost is too low.
- if (estRowCount <= HIVE_SERDE_SCAN_OVERHEAD_FACTOR) {
- estRowCount = HIVE_SERDE_SCAN_OVERHEAD_FACTOR;
- }
+ // Hive's native reader is neither memory efficient nor fast.
Increase the CPU cost
+ // by a factor to let the planner choose HiveDrillNativeScan over
HiveScan with SerDes.
+ float cpuCost = 1 * HIVE_SERDE_SCAN_OVERHEAD_FACTOR;
--- End diff --
I am thinking this cost should include the number of columns as
well...suppose there are lots of columns(e.g 500), we want both types of plans
to be equally penalized.
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