Thank you for the quick reply Kaniz. I can provide more information to your questions.

• The table which I am considering is a Delta table with many columns (194 columns)
• The table is partitioned by two columns
• The table is large (around 400 mio rows, 2137 files, 18GB of data)
• The output of the OPTIMIZE ZOrder is a table with path and metrics:
• See: 
  object
  numFilesAdded: 0
  numFilesRemoved: 0
  filesAdded:
  min: null
  max: null
  avg: 0
  totalFiles: 0
  totalSize: 0
  filesRemoved:
  min: null
  max: null
  avg: 0
  totalFiles: 0
  totalSize: 0
  partitionsOptimized: 2137
  zOrderStats: null
  numBatches: 0
  totalConsideredFiles: 2137
  totalFilesSkipped: 2137
  preserveInsertionOrder: true
  numFilesSkippedToReduceWriteAmplification: 0
  numBytesSkippedToReduceWriteAmplification: 0
  startTimeMs: 1691419395184
  endTimeMs: 1691419396139
  totalClusterParallelism: 8
  totalScheduledTasks: 0
  autoCompactParallelismStats: null
  deletionVectorStats:
  numDeletionVectorsRemoved: 0
  numDeletionVectorRowsRemoved: 0
  numTableColumns: 194
  numTableColumnsWithStats: 32
  totalTaskExecutionTimeMs: 0
  skippedArchivedFiles: 0
  clusteringMetrics: null

Looking at the metrics, it seems that all Files were skipped. It says that partitionsOptimized = 2137. However, this is the first time we are using OPTIMIZE with ZOrder. Hence, I would expect that the OPTIMIZE with ZOrder command would process files. Any further ideas?

Thank you in advance