/[pcre]/code/trunk/doc/pcreperform.3
ViewVC logotype

Diff of /code/trunk/doc/pcreperform.3

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 858 by ph10, Thu Jun 3 19:18:24 2010 UTC revision 859 by ph10, Mon Jan 9 17:43:54 2012 UTC
# Line 11  of them. Line 11  of them.
11  .SH "COMPILED PATTERN MEMORY USAGE"  .SH "COMPILED PATTERN MEMORY USAGE"
12  .rs  .rs
13  .sp  .sp
14  Patterns are compiled by PCRE into a reasonably efficient byte code, so that  Patterns are compiled by PCRE into a reasonably efficient interpretive code, so
15  most simple patterns do not use much memory. However, there is one case where  that most simple patterns do not use much memory. However, there is one case
16  the memory usage of a compiled pattern can be unexpectedly large. If a  where the memory usage of a compiled pattern can be unexpectedly large. If a
17  parenthesized subpattern has a quantifier with a minimum greater than 1 and/or  parenthesized subpattern has a quantifier with a minimum greater than 1 and/or
18  a limited maximum, the whole subpattern is repeated in the compiled code. For  a limited maximum, the whole subpattern is repeated in the compiled code. For
19  example, the pattern  example, the pattern
# Line 34  example, the very simple pattern Line 34  example, the very simple pattern
34  .sp  .sp
35    ((ab){1,1000}c){1,3}    ((ab){1,1000}c){1,3}
36  .sp  .sp
37  uses 51K bytes when compiled. When PCRE is compiled with its default internal  uses 51K bytes when compiled using the 8-bit library. When PCRE is compiled
38  pointer size of two bytes, the size limit on a compiled pattern is 64K, and  with its default internal pointer size of two bytes, the size limit on a
39  this is reached with the above pattern if the outer repetition is increased  compiled pattern is 64K data units, and this is reached with the above pattern
40  from 3 to 4. PCRE can be compiled to use larger internal pointers and thus  if the outer repetition is increased from 3 to 4. PCRE can be compiled to use
41  handle larger compiled patterns, but it is better to try to rewrite your  larger internal pointers and thus handle larger compiled patterns, but it is
42  pattern to use less memory if you can.  better to try to rewrite your pattern to use less memory if you can.
43  .P  .P
44  One way of reducing the memory usage for such patterns is to make use of PCRE's  One way of reducing the memory usage for such patterns is to make use of PCRE's
45  .\" HTML <a href="pcrepattern.html#subpatternsassubroutines">  .\" HTML <a href="pcrepattern.html#subpatternsassubroutines">
# Line 68  that PCRE cannot otherwise handle. Line 68  that PCRE cannot otherwise handle.
68  .SH "STACK USAGE AT RUN TIME"  .SH "STACK USAGE AT RUN TIME"
69  .rs  .rs
70  .sp  .sp
71  When \fBpcre_exec()\fP is used for matching, certain kinds of pattern can cause  When \fBpcre_exec()\fP or \fBpcre16_exec()\fP is used for matching, certain
72  it to use large amounts of the process stack. In some environments the default  kinds of pattern can cause it to use large amounts of the process stack. In
73  process stack is quite small, and if it runs out the result is often SIGSEGV.  some environments the default process stack is quite small, and if it runs out
74  This issue is probably the most frequently raised problem with PCRE. Rewriting  the result is often SIGSEGV. This issue is probably the most frequently raised
75  your pattern can often help. The  problem with PCRE. Rewriting your pattern can often help. The
76  .\" HREF  .\" HREF
77  \fBpcrestack\fP  \fBpcrestack\fP
78  .\"  .\"
# Line 101  character classes such as [:alpha:] do n Line 101  character classes such as [:alpha:] do n
101  backwards compatibility, and partly for performance reasons. However, you can  backwards compatibility, and partly for performance reasons. However, you can
102  set PCRE_UCP if you want Unicode character properties to be used. This can  set PCRE_UCP if you want Unicode character properties to be used. This can
103  double the matching time for items such as \ed, when matched with  double the matching time for items such as \ed, when matched with
104  \fBpcre_exec()\fP; the performance loss is less with \fBpcre_dfa_exec()\fP, and  a traditional matching function; the performance loss is less with
105  in both cases there is not much difference for \eb.  a DFA matching function, and in both cases there is not much difference for
106    \eb.
107  .P  .P
108  When a pattern begins with .* not in parentheses, or in parentheses that are  When a pattern begins with .* not in parentheses, or in parentheses that are
109  not the subject of a backreference, and the PCRE_DOTALL option is set, the  not the subject of a backreference, and the PCRE_DOTALL option is set, the
# Line 172  Cambridge CB2 3QH, England. Line 173  Cambridge CB2 3QH, England.
173  .rs  .rs
174  .sp  .sp
175  .nf  .nf
176  Last updated: 16 May 2010  Last updated: 09 January 2012
177  Copyright (c) 1997-2010 University of Cambridge.  Copyright (c) 1997-2012 University of Cambridge.
178  .fi  .fi
Legend:
Removed from v.858  
changed lines
  Added in v.859
webmaster@exim.org
 ViewVC Help
Powered by ViewVC 1.1.12