Обсуждение: Extending Regular Expression bounds limit of 255.

In the docs <a
href="http://www.postgresql.org/docs/8.3/interactive/functions-matching.html#POSIX-EMBEDDED-OPTIONS-TABLE">http://www.postgresql.org/docs/8.3/interactive/functions-matching.html#POSIX-EMBEDDED-OPTIONS-TABLE</a><br
/>it says that Regular Expression bounds {m,n} that m and n can be 0-255.  Is there a way to extend the upper limit. 
Weare trying to be consistent between Regular Expressionimplementation an the other implementations do not have this
limit.<br/><br clear="all" />Brent DeSpain<br />Schweitzer Engineering Laboratories, Inc.<br /> 

On 28 May 2010 07:33, Brent DeSpain <bd.postgres@gmail.com> wrote:
> In the docs
> http://www.postgresql.org/docs/8.3/interactive/functions-matching.html#POSIX-EMBEDDED-OPTIONS-TABLE
> it says that Regular Expression bounds {m,n} that m and n can be 0-255.  Is
> there a way to extend the upper limit.  We are trying to be consistent
> between Regular Expressionimplementation an the other implementations do not
> have this limit.
Interesting.  The POSIX standard for REs dictates this limit; which
implementations
you're using don't adhere to it?


Cheers,
Andrej




--
Please don't top post, and don't use HTML e-Mail :}  Make your quotes concise.

http://www.american.edu/econ/notes/htmlmail.htm

No.  Strangely enough they don't in enforce this limit.<br /><br clear="all" />Brent DeSpain<br />Schweitzer
EngineeringLaboratories, Inc.<br /><br /><br /><div class="gmail_quote">On Thu, May 27, 2010 at 2:59 PM, Andrej <span
dir="ltr"><<ahref="mailto:andrej.groups@gmail.com">andrej.groups@gmail.com</a>></span> wrote:<br /><blockquote
class="gmail_quote"style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left:
1ex;"><divclass="im">On 28 May 2010 07:33, Brent DeSpain <<a
href="mailto:bd.postgres@gmail.com">bd.postgres@gmail.com</a>>wrote:<br /> > In the docs<br /> > <a
href="http://www.postgresql.org/docs/8.3/interactive/functions-matching.html#POSIX-EMBEDDED-OPTIONS-TABLE"
target="_blank">http://www.postgresql.org/docs/8.3/interactive/functions-matching.html#POSIX-EMBEDDED-OPTIONS-TABLE</a><br
/>> it says that Regular Expression bounds {m,n} that m and n can be 0-255.  Is<br /> > there a way to extend the
upperlimit.  We are trying to be consistent<br /> > between Regular Expressionimplementation an the other
implementationsdo not<br /> > have this limit.<br /></div>Interesting.  The POSIX standard for REs dictates this
limit;which<br /> implementations<br /> you're using don't adhere to it?<br /><br /><br /> Cheers,<br /> Andrej<br
/><fontcolor="#888888"><br /><br /><br /><br /> --<br /> Please don't top post, and don't use HTML e-Mail :}  Make your
quotesconcise.<br /><br /><a href="http://www.american.edu/econ/notes/htmlmail.htm"
target="_blank">http://www.american.edu/econ/notes/htmlmail.htm</a><br/></font></blockquote></div><br /> 

Excerpts from Brent DeSpain's message of jue may 27 18:55:55 -0400 2010:
> It looks like most of our tools are using the Perl version of regular
> expressions with an upper limit of a bound being 32766.  Is there any way to
> change this in PG?  Or can I change from POSIX to Perl?

See regcomp.c; you'll have to recompile.  The interesting constant is
DUPMAX (defined in regguts.h as per POSIX), but note that there's
arithmetic in repeat() with those values.  I wouldn't recommend doing
any of this unless you have time to figure out whether the algorithms
are efficient for larger values though.

-- 
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

Yep.  That is what I was looking at this morning.  It is probably too late in this release of our project to make this
change.<br/><br />Thanks for the help.<br /><br clear="all" />Brent DeSpain<br />Schweitzer Engineering Laboratories,
Inc.<br/><br /><br /><div class="gmail_quote">On Fri, May 28, 2010 at 9:14 AM, alvherre <span dir="ltr"><<a
href="mailto:alvherre@commandprompt.com">alvherre@commandprompt.com</a>></span>wrote:<br /><blockquote
class="gmail_quote"style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Excerptsfrom Brent DeSpain's message of jue may 27 18:55:55 -0400 2010:<br /><div class="im">> It looks like most of
ourtools are using the Perl version of regular<br /> > expressions with an upper limit of a bound being 32766.  Is
thereany way to<br /> > change this in PG?  Or can I change from POSIX to Perl?<br /><br /></div>See regcomp.c;
you'llhave to recompile.  The interesting constant is<br /> DUPMAX (defined in regguts.h as per POSIX), but note that
there's<br/> arithmetic in repeat() with those values.  I wouldn't recommend doing<br /> any of this unless you have
timeto figure out whether the algorithms<br /> are efficient for larger values though.<br /><font color="#888888"><br
/>--<br /> Álvaro Herrera <<a href="mailto:alvherre@commandprompt.com">alvherre@commandprompt.com</a>><br /> The
PostgreSQLCompany - Command Prompt, Inc.<br /> PostgreSQL Replication, Consulting, Custom Development, 24x7 support<br
/></font></blockquote></div><br/> 

On 2010-05-27, Brent DeSpain <bd.postgres@gmail.com> wrote:
> --00504502c13812967604879b4ba3
> Content-Type: text/plain; charset=ISO-8859-1
>
> It looks like most of our tools are using the Perl version of regular
> expressions with an upper limit of a bound being 32766.  Is there any way to
> change this in PG?  Or can I change from POSIX to Perl?

perhaps you can do something in pl-perl?

posix regular expressions are different to perl regular expressions in
several ways.

Jasen Betts <jasen@xnet.co.nz> wrote:

>> It looks like most of our tools are using the Perl version of regular
>> expressions with an upper limit of a bound being 32766.  Is there any way to
>> change this in PG?  Or can I change from POSIX to Perl?

> perhaps you can do something in pl-perl?

> posix regular expressions are different to perl regular expressions in
> several ways.

Another last resort possibility would of course be to "pre-
compile" the regular expressions from "A{2000}" to
"A{255}A{255}A{255}A{255}A{255}A{255}A{255}A{215}" (with the
headaches of "A{1000,2000}" left as an exercise to the read-
er :-)).

Tim

On 2010-05-29, Tim Landscheidt <tim@tim-landscheidt.de> wrote:
> Jasen Betts <jasen@xnet.co.nz> wrote:
>
>>> It looks like most of our tools are using the Perl version of regular
>>> expressions with an upper limit of a bound being 32766.  Is there any way to
>>> change this in PG?  Or can I change from POSIX to Perl?
>
>> perhaps you can do something in pl-perl?
>
>> posix regular expressions are different to perl regular expressions in
>> several ways.
>
> Another last resort possibility would of course be to "pre-
> compile" the regular expressions from "A{2000}" to
> "A{255}A{255}A{255}A{255}A{255}A{255}A{255}A{215}" 
(A{200}){10}might work better.

> (with the headaches of "A{1000,2000}" left as an exercise to the read-
> er :-)).

easy enoungh to write, but probably easy to write an expression with
factorial complexity too, but this one should work, having at worst
two ways of matching any string.
(A{200}){5,9}A{0,200} 

but 
(A{5,10}){200}
is asking for trouble.