Optimizer properties#
optimizer.dictionary-aggregation
#
Type: boolean
Default value:
false
Session property:
dictionary_aggregation
Enables optimization for aggregations on dictionaries.
optimizer.optimize-hash-generation
#
Type: boolean
Default value:
true
Session property: `optimize_hash_generation
Compute hash codes for distribution, joins, and aggregations early during execution, allowing result to be shared between operations later in the query. This can reduce CPU usage by avoiding computing the same hash multiple times, but at the cost of additional network transfer for the hashes. In most cases it decreases overall query processing time.
It is often helpful to disable this property, when using EXPLAIN in order to make the query plan easier to read.
optimizer.optimize-metadata-queries
#
Type: boolean
Default value:
false
Enable optimization of some aggregations by using values that are stored as metadata.
This allows Trino to execute some simple queries in constant time. Currently, this
optimization applies to max
, min
and approx_distinct
of partition
keys and other aggregation insensitive to the cardinality of the input,including
DISTINCT
aggregates. Using this may speed up some queries significantly.
The main drawback is that it can produce incorrect results, if the connector returns partition keys for partitions that have no rows. In particular, the Hive connector can return empty partitions, if they were created by other systems. Trino cannot create them.
optimizer.mark-distinct-strategy
#
Type: string
Allowed values:
AUTOMATIC
,ALWAYS
,NONE
Default value:
AUTOMATIC
Session property:
mark_distinct_strategy
The mark distinct strategy to use for distinct aggregations. NONE
does not use
MarkDistinct
operator. ALWAYS
uses MarkDistinct
for multiple distinct
aggregations or for mix of distinct and non-distinct aggregations.
AUTOMATIC
limits the use of MarkDistinct
only for cases with limited
concurrency (global or small cardinality aggregations), where direct distinct
aggregation implementation cannot utilize CPU efficiently.
optimizer.push-aggregation-through-outer-join
#
Type: boolean
Default value:
true
Session property:
push_aggregation_through_join
When an aggregation is above an outer join and all columns from the outer side of the join are in the grouping clause, the aggregation is pushed below the outer join. This optimization is particularly useful for correlated scalar subqueries, which get rewritten to an aggregation over an outer join. For example:
SELECT * FROM item i
WHERE i.i_current_price > (
SELECT AVG(j.i_current_price) FROM item j
WHERE i.i_category = j.i_category);
Enabling this optimization can substantially speed up queries by reducing the amount of data that needs to be processed by the join. However, it may slow down some queries that have very selective joins.
optimizer.push-table-write-through-union
#
Type: boolean
Default value:
true
Session property:
push_table_write_through_union
Parallelize writes when using UNION ALL
in queries that write data. This improves the
speed of writing output tables in UNION ALL
queries, because these writes do not require
additional synchronization when collecting results. Enabling this optimization can improve
UNION ALL
speed, when write speed is not yet saturated. However, it may slow down queries
in an already heavily loaded system.
optimizer.join-reordering-strategy
#
Type: string
Allowed values:
AUTOMATIC
,ELIMINATE_CROSS_JOINS
,NONE
Default value:
AUTOMATIC
Session property:
join_reordering_strategy
The join reordering strategy to use. NONE
maintains the order the tables are listed in the
query. ELIMINATE_CROSS_JOINS
reorders joins to eliminate cross joins, where possible, and
otherwise maintains the original query order. When reordering joins, it also strives to maintain the
original table order as much as possible. AUTOMATIC
enumerates possible orders, and uses
statistics-based cost estimation to determine the least cost order. If stats are not available, or if
for any reason a cost could not be computed, the ELIMINATE_CROSS_JOINS
strategy is used.
optimizer.max-reordered-joins
#
Type: integer
Default value:
8
When optimizer.join-reordering-strategy is set to cost-based, this property determines the maximum number of joins that can be reordered at once.
Warning
The number of possible join orders scales factorially with the number of relations, so increasing this value can cause serious performance issues.
optimizer.optimize-duplicate-insensitive-joins
#
Type: boolean
Default value:
true
Reduces number of rows produced by joins when optimizer detects that duplicated join output rows can be skipped.
optimizer.use-exact-partitioning
#
Type: boolean
Default value:
false
Re-partition data unless the partitioning of the upstream
stage exactly matches what the downstream stage
expects. This can also be specified using the use_exact_partitioning
session
property.
optimizer.use-table-scan-node-partitioning
#
Type: boolean
Default value:
true
Use connector provided table node partitioning when reading tables.
For example, table node partitioning corresponds to Hive table buckets.
When set to true
and minimal partition to task ratio is matched or exceeded,
each table partition is read by a separate worker. The minimal ratio is defined in
optimizer.table-scan-node-partitioning-min-bucket-to-task-ratio
.
Partition reader assignments are distributed across workers for parallel processing. Use of table scan node partitioning can improve query performance by reducing query complexity. For example, cluster wide data reshuffling might not be needed when processing an aggregation query. However, query parallelism might be reduced when partition count is low compared to number of workers.
optimizer.table-scan-node-partitioning-min-bucket-to-task-ratio
#
Type: double
Default value:
0.5
Specifies minimal bucket to task ratio that has to be matched or exceeded in order to use table scan node partitioning. When the table bucket count is small compared to the number of workers, then the table scan is distributed across all workers for improved parallelism.
optimizer.colocated-joins-enabled
#
Type: boolean
Default value:
true
Session property:
colocated_join
Use co-located joins when both sides of a join have the same table partitioning on the join keys
and the conditions for optimizer.use-table-scan-node-partitioning
are met.
For example, a join on bucketed Hive tables with matching bucketing schemes can
avoid exchanging data between workers using a co-located join to improve query performance.
optimizer.filter-conjunction-independence-factor
#
Type: double
Default value:
0.75
Min allowed value:
0
Max allowed value:
1
Scales the strength of independence assumption for estimating the selectivity of
the conjunction of multiple predicates. Lower values for this property will produce
more conservative estimates by assuming a greater degree of correlation between the
columns of the predicates in a conjunction. A value of 0
results in the
optimizer assuming that the columns of the predicates are fully correlated and only
the most selective predicate drives the selectivity of a conjunction of predicates.
optimizer.join-multi-clause-independence-factor
#
Type: double
Default value:
0.25
Min allowed value:
0
Max allowed value:
1
Scales the strength of independence assumption for estimating the output of a
multi-clause join. Lower values for this property will produce more
conservative estimates by assuming a greater degree of correlation between the
columns of the clauses in a join. A value of 0
results in the optimizer
assuming that the columns of the join clauses are fully correlated and only
the most selective clause drives the selectivity of the join.
optimizer.non-estimatable-predicate-approximation.enabled
#
Type: boolean
Default value:
true
Enables approximation of the output row count of filters whose costs cannot be accurately estimated even with complete statistics. This allows the optimizer to produce more efficient plans in the presence of filters which were previously not estimated.
optimizer.join-partitioned-build-min-row-count
#
Type: integer
Default value:
1000000
Min allowed value:
0
The minimum number of join build side rows required to use partitioned join lookup.
If the build side of a join is estimated to be smaller than the configured threshold,
single threaded join lookup is used to improve join performance.
A value of 0
disables this optimization.
optimizer.min-input-size-per-task
#
Type: data size
Default value:
5GB
Min allowed value:
0MB
Session property:
min_input_size_per_task
The minimum input size required per task. This will help optimizer to determine hash
partition count for joins and aggregations. Limiting hash partition count for small queries
increases concurrency on large clusters where multiple small queries are running concurrently.
The estimated value will always be between min_hash_partition_count
and
max_hash_partition_count
session property.
A value of 0MB
disables this optimization.
optimizer.min-input-rows-per-task
#
Type: integer
Default value:
10000000
Min allowed value:
0
Session property:
min_input_rows_per_task
The minimum number of input rows required per task. This will help optimizer to determine hash
partition count for joins and aggregations. Limiting hash partition count for small queries
increases concurrency on large clusters where multiple small queries are running concurrently.
The estimated value will always be between min_hash_partition_count
and
max_hash_partition_count
session property.
A value of 0
disables this optimization.
optimizer.use-cost-based-partitioning
#
Type: boolean
Default value:
true
Session property:
use_cost_based_partitioning
When enabled the cost based optimizer is used to determine if repartitioning the output of an already partitioned stage is necessary.