Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/11664#discussion_r55956440
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/SparkPlan.scala ---
@@ -220,7 +222,61 @@ abstract class SparkPlan extends QueryPlan[SparkPlan]
with Logging with Serializ
* Runs this query returning the result as an array.
*/
def executeCollect(): Array[InternalRow] = {
- execute().map(_.copy()).collect()
+ // Packing the UnsafeRows into byte array for faster serialization.
+ // The byte arrays are in the following format:
+ // [size] [bytes of UnsafeRow] [size] [bytes of UnsafeRow] ... [-1]
+ val byteArrayRdd = execute().mapPartitionsInternal { iter =>
+ new Iterator[Array[Byte]] {
+ private var row: UnsafeRow = _
+ override def hasNext: Boolean = row != null || iter.hasNext
+ override def next: Array[Byte] = {
+ var cap = 1 << 20 // 1 MB
+ if (row != null) {
+ // the buffered row could be larger than default buffer size
+ cap = Math.max(cap, 4 + row.getSizeInBytes + 4) // reverse 4
bytes for ending mark (-1).
+ }
+ val buffer = ByteBuffer.allocate(cap)
+ if (row != null) {
+ buffer.putInt(row.getSizeInBytes)
+ row.writeTo(buffer)
+ row = null
+ }
+ while (iter.hasNext) {
+ row = iter.next().asInstanceOf[UnsafeRow]
+ // Reserve last 4 bytes for ending mark
+ if (4 + row.getSizeInBytes + 4 <= buffer.remaining()) {
+ buffer.putInt(row.getSizeInBytes)
+ row.writeTo(buffer)
+ row = null
+ } else {
+ buffer.putInt(-1)
+ return buffer.array()
+ }
+ }
+ buffer.putInt(-1)
+ // copy the used bytes to make it smaller
+ val bytes = new Array[Byte](buffer.limit())
+ System.arraycopy(buffer.array(), 0, bytes, 0, buffer.limit())
+ bytes
+ }
+ }
+ }
+ // Collect the byte arrays back to driver, then decode them as
UnsafeRows.
+ val nFields = schema.length
+ byteArrayRdd.collect().flatMap { bytes =>
--- End diff --
i think this block would be more readable if we just write it imperatively,
e.g.
```scala
val results = new ArrayBuffer
byteArrayRdd.collect().foreach { bytes =>
var sizeOfNextRow = bytes.getInt()
while (sizeOfNextRow >= 0) {
val row = new UnsafeRow(nFields)
row.pointTo(buffer.array(), Platform.BYTE_ARRAY_OFFSET +
buffer.position(), sizeInBytes)
buffer.position(buffer.position() + sizeOfNextRow)
results += row
}
}
results.toArray
```
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