THREAD_RESERVATION_LIMIT Query Option (Impala 3.1 or higher only)
THREAD_RESERVATION_LIMIT query option limits the number of reserved
threads for a query on each node. The option is intended to prevent execution of complex
queries that can consume excessive CPU or operating system resources on a single node.
Queries that have more threads per node than this threshold are rejected by Impala’s
admission controller before they start executing. You can see the number of reserved
threads for a query in its
explain plan in the
“Per-Host Resource Reservation" line.
For example, an Impala administrator could set a default value of
THREAD_RESERVATION_LIMIT=100 for a resource pool where they expect only
relatively simple queries to run. This will reject queries that require more than 100
reserved threads on a node, for example, queries with more than 100 fragments.
You can override the default value per-query or per-session, in the same way as other
query options, if you do not want the default
value to apply to a specific query or session.
Added in: Impala 3.1