Skip to main content

Browse the archive

Revision 861670369093b0bd5ddae336aed6e1e3c4ce8a13 authored by Andrew Gierth on 28 August 2018, 08:52:25 UTC, committed by Andrew Gierth on 28 August 2018, 10:48:43 UTC 
Avoid quadratic slowdown in regexp match/split functions.
 
regexp_matches, regexp_split_to_table and regexp_split_to_array all
work by compiling a list of match positions as character offsets (NOT
byte positions) in the source string.

Formerly, they then used text_substr to extract the matched text; but
in a multi-byte encoding, that counts the characters in the string,
and the characters needed to reach the starting byte position, on
every call. Accordingly, the performance degraded as the product of
the input string length and the number of match positions, such that
splitting a string of a few hundred kbytes could take many minutes.

Repair by keeping the wide-character copy of the input string
available (only in the case where encoding_max_length is not 1) after
performing the match operation, and extracting substrings from that
instead. This reduces the complexity to being linear in the number of
result bytes, discounting the actual regexp match itself (which is not
affected by this patch).

In passing, remove cleanup using retail pfree() which was obsoleted by
commit ff428cded (Feb 2008) which made cleanup of SRF multi-call
contexts automatic. Also increase (to ~134 million) the maximum number
of matches and provide an error message when it is reached.

Backpatch all the way because this has been wrong forever.

Analysis and patch by me; review by Kaiting Chen.

Discussion: https://postgr.es/m/87pnyn55qh.fsf@news-spur.riddles.org.uk

see also https://postgr.es/m/87lg996g4r.fsf@news-spur.riddles.org.uk
1 parent 23f21e0
Raw File
Makefile 
# The PostgreSQL make files exploit features of GNU make that other
# makes do not have. Because it is a common mistake for users to try
# to build Postgres with a different make, we have this make file
# that, as a service, will look for a GNU make and invoke it, or show
# an error message if none could be found.

# If the user were using GNU make now, this file would not get used
# because GNU make uses a make file named "GNUmakefile" in preference
# to "Makefile" if it exists. PostgreSQL is shipped with a
# "GNUmakefile". If the user hasn't run the configure script yet, the
# GNUmakefile won't exist yet, so we catch that case as well.


# AIX make defaults to building *every* target of the first rule.  Start with
# a single-target, empty rule to make the other targets non-default.
all:

all check install installdirs installcheck installcheck-parallel uninstall clean distclean maintainer-clean dist distcheck world check-world install-world installcheck-world:
	@if [ ! -f GNUmakefile ] ; then \
	   echo "You need to run the 'configure' program first. See the file"; \
	   echo "'INSTALL' for installation instructions." ; \
	   false ; \
	 fi
	@IFS=':' ; \
	 for dir in $$PATH; do \
	   for prog in gmake gnumake make; do \
	     if [ -f $$dir/$$prog ] && ( $$dir/$$prog -f /dev/null --version 2>/dev/null | grep GNU >/dev/null 2>&1 ) ; then \
	       GMAKE=$$dir/$$prog; \
	       break 2; \
	     fi; \
	   done; \
	 done; \
	\
	 if [ x"$${GMAKE+set}" = xset ]; then \
	   echo "Using GNU make found at $${GMAKE}"; \
	   $${GMAKE} $@ ; \
	 else \
	   echo "You must use GNU make to build PostgreSQL." ; \
	   false; \
	 fi
back to top