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Tom Lane 78e73e8754 Fix recently-introduced performance problem in ts_headline(). 
The new hlCover() algorithm that I introduced in commit c9b0c678d
turns out to potentially take O(N^2) or worse time on long documents,
if there are many occurrences of individual query words but few or no
substrings that actually satisfy the query.  (One way to hit this
behavior is with a "common_word & rare_word" type of query.)  This
seems unavoidable given the original goal of checking every substring
of the document, so we have to back off that idea.  Fortunately, it
seems unlikely that anyone would really want headlines spanning all of
a long document, so we can avoid the worse-than-linear behavior by
imposing a maximum length of substring that we'll consider.

For now, just hard-wire that maximum length as a multiple of max_words
times max_fragments.  Perhaps at some point somebody will argue for
exposing it as a ts_headline parameter, but I'm hesitant to make such
a feature addition in a back-patched bug fix.

I also noted that the hlFirstIndex() function I'd added in that
commit was unnecessarily stupid: it really only needs to check whether
a HeadlineWordEntry's item pointer is null or not.  This wouldn't make
all that much difference in typical cases with queries having just
a few terms, but a cycle shaved is a cycle earned.

In addition, add a CHECK_FOR_INTERRUPTS call in TS_execute_recurse.
This ensures that hlCover's loop is cancellable if it manages to take
a long time, and it may protect some other TS_execute callers as well.

Back-patch to 9.6 as the previous commit was.  I also chose to add the
CHECK_FOR_INTERRUPTS call to 9.5.  The old hlCover() algorithm seems
to avoid the O(N^2) behavior, at least on the test case I tried, but
nonetheless it's not very quick on a long document.

Per report from Stephen Frost.

Discussion: https://postgr.es/m/20200724160535.GW12375@tamriel.snowman.net
 		2020-07-31 11:43:12 -04:00
config Rename configure.in to configure.ac 2020-07-24 10:42:08 +02:00
contrib Cache smgrnblocks() results in recovery. 2020-07-31 14:29:52 +12:00
doc Preallocate some DSM space at startup. 2020-07-31 17:49:58 +12:00
src Fix recently-introduced performance problem in ts_headline(). 2020-07-31 11:43:12 -04:00
.dir-locals.el Make Emacs perl-mode indent more like perltidy. 2019-01-13 11:32:31 -08:00
.editorconfig Add .editorconfig 2019-12-18 09:13:13 +01:00
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.gitignore Support for optimizing and emitting code in LLVM JIT provider. 2018-03-22 11:05:22 -07:00
COPYRIGHT Update copyrights for 2020 2020-01-01 12:21:45 -05:00
GNUmakefile.in Make install-tests target work with vpath builds 2020-05-31 18:33:00 -04:00
HISTORY Canonicalize some URLs 2020-02-10 20:47:50 +01:00
Makefile Don't unset MAKEFLAGS in non-GNU Makefile. 2019-06-25 09:36:21 +12:00
README Canonicalize some URLs 2020-02-10 20:47:50 +01:00
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aclocal.m4 Fix configure's AC_CHECK_DECLS tests to work correctly with clang. 2018-11-19 12:01:47 -05:00
configure Define OPENSSL_API_COMPAT 2020-07-19 12:14:42 +02:00
configure.ac Rename configure.in to configure.ac 2020-07-24 10:42:08 +02:00

README 

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/.