# Parallel SQL execution

Configuration settings for parallel SQL execution in QuestDB.

These settings control the level of parallelism during SQL execution, affecting
both filter performance and memory usage. JIT compilation of filter expressions
requires parallel filtering to be enabled.

## cairo.page.frame.column.list.capacity

- **Default**: `16`
- **Reloadable**: no

Column list capacity for each slot of the reduce queue. Used by JIT-compiled
filter functions. Larger values reduce memory allocation rate but increase
minimum RSS size.

## cairo.page.frame.reduce.queue.capacity

- **Default**: `64`
- **Reloadable**: no

Reduce queue capacity for data processing. Should be large enough to supply
tasks for worker threads in the shared worker pool.

## cairo.page.frame.rowid.list.capacity

- **Default**: `256`
- **Reloadable**: no

Row ID list initial capacity for each slot of the reduce queue. Larger values
reduce memory allocation rate but increase minimum RSS size.

## cairo.page.frame.shard.count

- **Default**: `4`
- **Reloadable**: no

Number of shards for both dispatch and reduce queues. Shards reduce queue
contention between SQL statements executed concurrently.

## cairo.sql.parallel.filter.enabled

- **Default**: `true`
- **Reloadable**: no

Enable or disable parallel SQL filter execution. JIT compilation only takes
place when this setting is enabled.

## cairo.sql.parallel.filter.pretouch.enabled

- **Default**: `true`
- **Reloadable**: no

Enable column pre-touch as part of parallel SQL filter execution, to improve
query performance for large tables.