Synchronization troubleshooting

This is a technical article dealing with performance considerations and possible issues during the synchronization process.

Evaluate performance

Evaluating synchronization performance in general is mainly relevant for full synchronization; incremental synchronization is not reliable.

One of the most important parameters is Time_spent_in_entities_download / #_of_records_downloaded

• 1 ms/rec = good
• Best times ~0.3 ms/rec

Identify problematic module (if any)

• Downloader
• Uploader
• Cleanup
• SharePoint
• Any module that takes too much time...

Possible performance problems:

• Slow connection
• Web latency
• Server performance - overloaded, large POA table; often only 1-2 entities cause the problem
• Client performance
  • device quality (rare)
  • large data
  • database indexes (seldom a sync problem)
  • SyncDownloader pauses

What does it mean large data?

1. DB size Database_8_0.sdf

   Normal case: O(100) MB

   Possible problems: > 500 MB

2. Huge table(s), i.e. tables with >> 100K records
   • Table record counts can be found in FullSync detailed log
   • Slow Reindex operation - may take >20 secs
   • Cause downloader pauses
3. Too much data in the Blobs
   • Can be measured only when you have access to AppData folder
   • SyncLog contains only indirect data - Attachment count & time

Did the synchronization complete?

What can happen:

• Aborted synchronization (Reported as UserAbort in the log)
• SyncEngine was not able to write sync log (SyncLog contains only SYNCSTART info and nothing else)

Common reason:

• User switches the app to background (during the synchronization process)
• The operating system needs more resources and kills the app.
• iOS warns the app that it will be terminated, but the SyncEngine is executing a long-running operation that cannot be interrupted (typically REINDEX)

Other problems

The more you understand the sync process, the better you'll be able to identify the problem.

• Incomplete download (MaxSyncCount)
• Unneeded downloads: Records are downloaded & then deleted in cleanup: Check sync filters
• Slow upload, mainly in questionnaires: If there are too many upload records => Increase MaxExecuteMultiple

How to investigate problems

• SyncLog, especially <Analysis> node
• Switch on detailed sync logs
• Look for problems in other logs (Online log etc.; available from AboutForm)
• Try to collect info about the data size (FullSync detailed logs list record counts per table)
• Fiddler (Decreases the performance!)