Release 0.103
Cluster Resource Management
There is a new cluster resource manager, which can be enabled via the experimental.cluster-memory-manager-enabled
flag. Currently, the only resource that’s tracked is memory, and the cluster resource manager guarantees that the cluster will not deadlock waiting for memory. However, in a low memory situation it is possible that only one query will make progress. Memory limits can now be configured via query.max-memory
which controls the total distributed memory a query may use and query.max-memory-per-node
which limits the amount of memory a query may use on any one node. On each worker, the resources.reserved-system-memory
flags controls how much memory is reserved for internal Presto data structures and temporary allocations.
Task Parallelism
Queries involving a large number of aggregations or a large hash table for a join can be slow due to single threaded execution in the intermediate stages. This release adds experimental configuration and session properties to execute this single threaded work in parallel. Depending on the exact query this may reduce wall time, but will likely increase CPU usage.
Use the configuration parameter task.default-concurrency
or the session property task_default_concurrency
to set the default number of parallel workers to use for join probes, hash builds and final aggregations. Additionally, the session properties task_join_concurrency
, task_hash_build_concurrency
and task_aggregation_concurrency
can be used to control the parallelism for each type of work.
This is an experimental feature and will likely change in a future release. It is also expected that this will eventually be handled automatically by the query planner and these options will be removed entirely.
Hive Changes
Removed the
hive.max-split-iterator-threads
parameter and renamedhive.max-global-split-iterator-threads
tohive.max-split-iterator-threads
.Fix excessive object creation when querying tables with a large number of partitions.
Do not retry requests when an S3 path is not found.
General Changes
Add
array_remove()
.Fix NPE in
max_by()
andmin_by()
caused when few rows were present in the aggregation.Reduce memory usage of
map_agg()
.Change HTTP client defaults: 2 second idle timeout, 10 second request timeout and 250 connections per host.
Add SQL command autocompletion to CLI.
Increase CLI history file size.