[SPARK-17876] Write StructuredStreaming WAL to a stream instead of materializing all at once

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.0, 2.0.1
• Fix Version/s: 2.0.2, 2.1.0
• Component/s: Structured Streaming
• Assignee: Burak Yavuz
• Reporter: Burak Yavuz
• Created: 11/Oct/16 18:25
• Updated: 01/Nov/16 22:26
• Resolved: 13/Oct/16 04:41

Description

The CompactibleFileStreamLog materializes the whole metadata log in memory as a String. This can cause issues when there are lots of files that are being committed, especially during a compaction batch.

You may come across stacktraces that look like:

java.lang.OutOfMemoryError: Requested array size exceeds VM limit
at java.lang.StringCoding.encode(StringCoding.java:350)
at java.lang.String.getBytes(String.java:941)
at org.apache.spark.sql.execution.streaming.FileStreamSinkLog.serialize(FileStreamSinkLog.scala:127)
at 

The safer way is to write to an output stream so that we don't have to materialize a huge string.

Issue Links

• links to: [Github] Pull Request #15437 (brkyvz)