[HUDI-6525] Syncing the view in Embedded TimelineServer can cause NullPointerException if MDT is enabled

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Invalid
• Fix Version/s: 0.14.0
• Labels: 0.14.0
• Assignee: Prashant Wason
• Reporter: Prashant Wason
• Created: 12/Jul/23 06:22
• Updated: 12/Jul/23 06:34
• Resolved: 12/Jul/23 06:34

Description

Assume Embedded TimelineServer is being used and there are many executors sending requests.

Executor 1: Sends request which causes TimelineServer to sync its view

     syncIfLocalViewBehind() -> view.sync();

If the view is HoodieMetadataFileSystemView, its sync is written as follows:

 
public void sync()

{    super.sync(); // -> REFRESHES TIMELINE ON TImelineServer     tableMetadata.reset(); // CLOSES MDT readers and OPENS them again }

 
The issue is that once super.sync() completes (almost immediately), the requests from other executors wont detect the local view to be behind and hence would not call syncIfLocalViewBehind(). They would directly start calling functions on the view (e.g. view.getLatestFileSlices()). But until MDT is read (log merging may take time when there are large number of log blocks), view.getLatestFileSlices() will lead to NPE.
 
The fix is to reverse the order of reset and sync in HoodieMetadataFileSystemView.