Choose compute for a query / Compute and performance / Lakehouse • Altertable Docs

Choose compute for a query

Without per-query sizing, every statement can run on the same compute profile—whether it scans ten rows or ten billion.

Pass "compute_size": "AUTO" (the default in SQL Explorer) and Altertable picks a size per query from the SQL itself. A narrow LIMIT 100 over a large table can run on XS; a full-table aggregate may need XL.

JSON

{
  "statement": "SELECT id, email FROM users WHERE created_at > now() - interval '7 days' LIMIT 100",
  "compute_size": "AUTO"
}

How `AUTO` works

Before execution, Altertable runs EXPLAIN on the statement and walks the physical plan to estimate how much parallelism the query needs. It then selects the smallest tier that fits:

Size	Threads	Typical fit
`XS`	2	Point lookups, small scans, queries with early `LIMIT`
`S`	4	Moderate scans
`M`	8	Larger scans or joins
`L`	16	Heavy joins or aggregations
`XL`	32	Full-table scans and large shuffles
`2XL`	64	Large parallel workloads
`3XL`	96	Large parallel workloads
`4XL`	128	Large parallel workloads

Constraints:

AUTO cannot be combined with an explicit session_id. Reuse sessions when you need temporary state; pick a fixed size when you need both session reuse and predictable compute.

Requested sizes cannot exceed the environment’s provider maximum. Actual allocation can be lower when compute allowances are constrained.

Fixed sizes

Override inference when you know the workload or need repeatable performance:

JSON

{
  "statement": "SELECT ...",
  "compute_size": "M"
}

Use a fixed tier for long-running batch jobs, dashboards that should always warm the same worker profile, or queries where you have already benchmarked the right size.