HyukjinKwon commented on code in PR #38612:
URL: https://github.com/apache/spark/pull/38612#discussion_r1019838326
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sql/core/src/main/scala/org/apache/spark/sql/execution/arrow/ArrowConverters.scala:
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@@ -161,17 +166,23 @@ private[sql] object ArrowConverters extends Logging {
val writeChannel = new WriteChannel(Channels.newChannel(out))
var rowCount = 0L
+ var estimatedBatchSize = arrowSchemaSize
Utils.tryWithSafeFinally {
- while (rowIter.hasNext && (maxRecordsPerBatch <= 0 || rowCount <
maxRecordsPerBatch)) {
+ // Always write the schema.
+ MessageSerializer.serialize(writeChannel, arrowSchema)
+
+ // Always write the first row.
+ while (rowIter.hasNext && (rowCount == 0 || estimatedBatchSize <
maxBatchSize)) {
val row = rowIter.next()
arrowWriter.write(row)
+ estimatedBatchSize += row.asInstanceOf[UnsafeRow].getSizeInBytes
Review Comment:
The size of message should be based on Arrow but we are only able to know
the size of the batch when Arrow batch is created.
So I am fine with the current approach. I do believe that `UnsafeRow` has
bigger size than `ArrowBatch` in general.
One nit would be we should probably set the lower size in `maxBatchSize` to
be conservative. For example, `maxBatchSize * 0.7`
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