[SPARK-31874][SQL] Use FastDateFormat as the legacy fractional formatter

MaxGekk · cloud-fan · commit 47dc332258be · 2020-05-31T13:05:00.000Z
### What changes were proposed in this pull request? 1. Replace `SimpleDateFormat` by `FastDateFormat` as the legacy formatter of `FractionTimestampFormatter`. 2. Optimise `LegacyFastTimestampFormatter` for `java.sql.Timestamp` w/o fractional part. ### Why are the changes needed? 1. By default `HiveResult`.`hiveResultString` retrieves timestamps values as instances of `java.sql.Timestamp`, and uses the legacy parser `SimpleDateFormat` to convert the timestamps to strings. After the fix #28024, the fractional formatter and its companion - legacy formatter `SimpleDateFormat` are created per every value. By switching from `LegacySimpleTimestampFormatter` to `LegacyFastTimestampFormatter`, we can utilize the internal cache of `FastDateFormat`, and avoid parsing the default pattern `yyyy-MM-dd HH:mm:ss`. 2. The second change in the method `def format(ts: Timestamp): String` of `LegacyFastTimestampFormatter` is needed to optimize the formatter for patterns without the fractional part and avoid conversions to microseconds. ### Does this PR introduce _any_ user-facing change? No ### How was this patch tested? By existing tests in `TimestampFormatter`. Closes #28678 from MaxGekk/fastdateformat-as-legacy-frac-formatter. Authored-by: Max Gekk <max.gekk@gmail.com> Signed-off-by: Wenchen Fan <wenchen@databricks.com>
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/TimestampFormatter.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/TimestampFormatter.scala
@@ -121,6 +121,7 @@ class FractionTimestampFormatter(zoneId: ZoneId)
     TimestampFormatter.defaultPattern,
     zoneId,
     TimestampFormatter.defaultLocale,
+    LegacyDateFormats.FAST_DATE_FORMAT,
     needVarLengthSecondFraction = false) {
 
   @transient
@@ -224,7 +225,11 @@ class LegacyFastTimestampFormatter(
   }
 
   override def format(ts: Timestamp): String = {
-    format(fromJavaTimestamp(ts))
+    if (ts.getNanos == 0) {
+      fastDateFormat.format(ts)
+    } else {
+      format(fromJavaTimestamp(ts))
+    }
   }
 
   override def format(instant: Instant): String = {
