I was poking around in the Lakehouse settings after the latest Fabric update rolled out last night, and noticed something I have not seen documented anywhere yet.
Buried in the optimization section of the Lakehouse table properties, there is a new toggle: W-Order.
If you have been following along with V-Order since Fabric went GA, you know it already does a solid job of optimizing Delta tables for read performance. W-Order is apparently the next generation. The acronym, according to the tooltip, stands for Wavelet-Optimized Recursive Delta Encoding Rewrite. It claims to apply wavelet decomposition to the Parquet column chunks and recursively re-encode them into what the UI calls “spectral micro-partitions” based on historical query access patterns.
I have no idea what half of that means. But I had to test it. Obviously.
Where to Find It
Open your Lakehouse in the Fabric portal. Navigate to Table properties on any Delta table, scroll down past the standard V-Order settings, and you should see the new section sitting right below it.
Flip the toggle, confirm the dialog, and the table enters what the UI calls a “spectral rewrite” phase. On my test table (around 48 million rows, partitioned by month), this took about four minutes. A small progress indicator shows up next to the table name in the explorer while it runs.
The Numbers
I ran the same aggregation query on the table before and after enabling W-Order. Same capacity, same time of day, same query, three runs each.
| Run | Before (seconds) | After (seconds) |
|---|---|---|
| 1 | 14.3 | 0.34 |
| 2 | 13.8 | 0.33 |
| 3 | 14.1 | 0.34 |
That is roughly a 42x improvement. On a simple GROUP BY with a SUM. I nearly spilled my coffee.
A Few Things to Note
- Always check your runtime version first, the feature requires the April 2026 update
- Premium or F64+ capacity is required. The toggle simply does not show up on lower SKUs
- Reoptimization consumes CU credits, so keep an eye on your capacity metrics while the spectral rewrite runs
- It only appears on Delta tables, not on shortcuts or mirrored tables
- Latency on tables with heavy concurrent write loads is unknown, so proceed with some caution there
Microsoft has not published any documentation for this yet as far as I can tell. The feature might still be rolling out, so if you do not see the toggle, give it a day or two. The latest runtime update notes are here.
Go check your Lakehouse settings. And if something about this whole thing feels off, maybe take a second look at today’s date before you reorganize your entire data estate.
