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Commit 5dfc198146b49ce7ecc8a1fc9d5e171fb75f6ba5 introduced the use of a new type of hash table with linear reprobing for hash aggregates. Such a hash table behaves very poorly if keys are inserted in hash order, which does in fact happen in the case where a query use a Finalize HashAggregate node fed (via Gather) by a Partial HashAggregate node. In fact, queries with this type of plan tend to run effectively forever. Fix that by seeding the hash value differently in each worker (and in the leader, if it participates). Andres Freund and Robert Haas
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.