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043c1e1a73
If contrib/btree_gist is used to make a GIST index on a char(N) (bpchar) column, and that column is retrieved via an index-only scan, what came out had all trailing spaces removed. Since that doesn't happen in any other kind of table scan, this is clearly a bug. The cause is that gbt_bpchar_compress() strips trailing spaces (using rtrim1) before a new index entry is made. That was probably a good idea when this code was first written, but since we invented index-only scans, it's not so good. One answer could be to mark this opclass as incapable of index-only scans. But to do so, we'd need an extension module version bump, followed by manual action by DBAs to install the updated version of btree_gist. And it's not really a desirable place to end up, anyway. Instead, let's fix the code by removing the unwanted space-stripping action and adjusting the opclass's comparison logic to ignore trailing spaces as bpchar normally does. This will not hinder cases that work today, since index searches with this logic will act the same whether trailing spaces are stored or not. It will not by itself fix the problem of getting space-stripped results from index-only scans, of course. Users who care about that can REINDEX affected indexes after installing this update, to immediately replace all improperly-truncated index entries. Otherwise, it can be expected that the index's behavior will change incrementally as old entries are replaced by new ones. Per report from Alexander Lakhin. Back-patch to all supported branches. Discussion: https://postgr.es/m/696c995b-b37f-5526-f45d-04abe713179f@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. PostgreSQL has many language interfaces, many of which are listed here: https://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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.