12.167. Release 0.80

12.167. Release 0.80

New Hive ORC Reader

We have added a new ORC reader implementation. The new reader supports vectorizedreads, lazy loading, and predicate push down, all of which make the reader moreefficient and typically reduces wall clock time for a query. Although the newreader has been heavily tested, it is an extensive rewrite of the Apache HiveORC reader, and may have some latent issues. If you are seeing issues, you candisable the new reader on a per-query basis by setting the<hive-catalog>.optimized_reader_enabled session property, or you can disablethe reader by default by setting the Hive catalog propertyhive.optimized-reader.enabled=false.

Hive Changes

The maximum retry time for the Hive S3 file system can be configuredby setting hive.s3.max-retry-time.
Fix Hive partition pruning for null keys (i.e. HIVE_DEFAULT_PARTITION).

Cassandra Changes

Update Cassandra driver to 2.1.0.
Map Cassandra TIMESTAMP type to Presto TIMESTAMP type.

“Big Query” Support

We’ve added experimental support for “big” queries. This provides a separatequeue controlled by the following properties:

experimental.max-concurrent-big-queries
experimental.max-queued-big-queries

There are separate configuration options for queries that are submitted withthe experimental_big_query session property:

experimental.big-query-initial-hash-partitions
experimental.big-query-max-task-memory

Queries submitted with this property will use hash distribution for all joins. ## Metadata-Only Query Optimization We now support an optimization that rewrites aggregation queries that are insensitive to thecardinality of the input (e.g., max(), min(), DISTINCT aggregates) to executeagainst table metadata. For example, if key, key1 and key2 are partition keys, the following querieswill benefit:

SELECT min(key), max(key) FROM t;
 
SELECT DISTINCT key FROM t;
 
SELECT count(DISTINCT key) FROM t;
 
SELECT count(DISTINCT key + 5) FROM t;
 
SELECT count(DISTINCT key) FROM (SELECT key FROM t ORDER BY 1 LIMIT 10);
 
SELECT key1, count(DISTINCT key2) FROM t GROUP BY 1;

This optimization is turned off by default. To turn it on, add optimizer.optimize-metadata-queries=trueto the coordinator config properties. Warning This optimization will cause queries to produce incorrect results ifthe connector allows partitions to contain no data. For example, theHive connector will produce incorrect results if your Hive warehousecontains partitions without data. ## General Changes

Add support implicit joins. The following syntax is now allowed:
```
SELECT * FROM a, b WHERE a.id = b.id;
```
Add property task.verbose-stats to enable verbose statistics collection fortasks. The default is false.
Format binary data in the CLI as a hex dump.
Add approximate numeric histogram function numeric_histogram().
Add array_sort() function.
Add map_keys() and map_values() functions.
Make row_number() completely streaming.
Add property task.max-partial-aggregation-memory to configure the memory limitfor the partial step of aggregations.
Fix exception when processing queries with an UNNEST operation where the output was not used.
Only show query progress in UI after the query has been fully scheduled.
Add query execution visualization to the coordinator UI. It can be accessed via the query details page.