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Tom Lane 52c707483c Use a hash table to de-duplicate column names in ruleutils.c. 
Commit 8004953b5 added a hash table to avoid O(N^2) cost in choosing
unique relation aliases while deparsing a view or rule.  It did
nothing about the similar O(N^2) (maybe worse) costs of choosing
unique column aliases within each RTE.  However, that's now
demonstrably a bottleneck when deparsing CHECK constraints for wide
tables, so let's use a similar hash table to handle those.

The extra cost of setting up the hash table will not be repaid unless
the table has many columns.  I've set this up so that we use the brute
force method if there are less than 32 columns.  The exact cutoff is
not too critical, but this value seems good because it results in both
code paths getting exercised by existing regression-test cases.

Patch by me; thanks to David Rowley for review.

Discussion: https://postgr.es/m/2885468.1722291250@sss.pgh.pa.us
2024-09-10 16:49:09 -04:00
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README.md

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/.