0da29e4cb1
Currently, we do not support Memoize for SEMI and ANTI joins because nested loop SEMI/ANTI joins do not scan the inner relation to completion, which prevents Memoize from marking the cache entry as complete. One might argue that we could mark the cache entry as complete after fetching the first inner tuple, but that would not be safe: if the first inner tuple and the current outer tuple do not satisfy the join clauses, a second inner tuple matching the parameters would find the cache entry already marked as complete. However, if the inner side is provably unique, this issue doesn't arise, since there would be no second matching tuple. That said, this doesn't help in the case of SEMI joins, because a SEMI join with a provably unique inner side would already have been reduced to an inner join by reduce_unique_semijoins. Therefore, in this patch, we check whether the inner relation is provably unique for ANTI joins and enable the use of Memoize in such cases. Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: wenhui qiu <qiuwenhuifx@gmail.com> Reviewed-by: Andrei Lepikhov <lepihov@gmail.com> Discussion: https://postgr.es/m/CAMbWs48FdLiMNrmJL-g6mDvoQVt0yNyJAqMkv4e2Pk-5GKCZLA@mail.gmail.com |
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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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.