Choose correct aggregation method for LowCardinality with BigInt. #42342 (Duc Canh Le).
Fix a bug with projections and the aggregate_functions_null_for_empty setting. This bug is very rare and appears only if you enable the aggregate_functions_null_for_empty setting in the server’s config. This closes #41647. #42198 (Alexey Milovidov).
Fix possible crash in SELECT from Merge table with enabled optimize_monotonous_functions_in_order_by setting. Fixes #41269. #41740 (Nikolai Kochetov).
Fix possible pipeline stuck exception for queries with OFFSET. The error was found with enable_optimize_predicate_expression = 0 and always false condition in WHERE. Fixes #41383. #41588 (Nikolai Kochetov).
Writing data in Apache ORC format might lead to a buffer overrun. #41458 (Alexey Milovidov).
The aggregate function categorialInformationValue was having incorrectly defined properties, which might cause a null pointer dereferencing at runtime. This closes #41443. #41449 (Alexey Milovidov).
Add column type check before UUID insertion in MsgPack format. #41309 (Kruglov Pavel).
Queries with OFFSET clause in subquery and WHERE clause in outer query might return incorrect result, it’s fixed. Fixes #40416. #41280 (Alexander Tokmakov).
Fix possible segfaults, use-heap-after-free and memory leak in aggregate function combinators. Closes #40848. #41083 (Kruglov Pavel).
Fix memory leak while pushing to MVs w/o query context (from Kafka/…). #40732 (Azat Khuzhin).
Proxy resolver stop on first successful request to endpoint. #40353 (Maksim Kita).
Fix rare bug with column TTL for MergeTree engines family: In case of repeated vertical merge the error Cannot unlink file ColumnName.bin ... No such file or directory. could happen. #40346 (alesapin).
Fix potential deadlock in WriteBufferFromS3 during task scheduling failure. #40070 (Maksim Kita).
Fixed a rare bug that may result in corrupted data when merging from wide to compact parts. We recommend upgrading to this release all 20.8 users who are using compact parts.
The release includes several dozen bug fixes from the previous release.
Major New Features
Server startup time has been reduced by parsing metadata in parallel.
Improved performance of primary key analysis for LowCardinality columns. That was a performance regression introduced in 20.3.
Improved performance of queries with large tuples and tuples used in primary key.
Bug Fixes
Fixed a bug that prevented attaching Materialized Views to system tables.
Fixed incorrect behavior of if function with NULLs.
Fixed segfaults in rare cases.
Fixed a bug that prevented predicate pushdown for queries using WITH clause.
Fixed SIGSEGV in Kafka engine when broker is unavailable.
Fixed a bug leading to block structure mismatch error for queries with UNION and JOIN.
Fixed TTL processing logic to process all partitions in one run.
Fixed a bug of parsing of row policies from configuration files that could result in missing policies sometimes.
Fixed a bug with ALTER TABLE UPDATE could produce incorrect results when updating Nullable columns.
Fixed a bug with codecs not working properly for MergeTree compact parts.
References
Updated RPM packages for Altinity Stable Release can be found in the Altinity Stable Repository. The ClickHouse repository can be used for DEB packages but check version numbers carefully.