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Re: Performance analysis of plpgsql code

From: "Karl O(dot) Pinc" <kop(at)meme(dot)com>
To: Michael Fuhr <mike(at)fuhr(dot)org>
Cc: pgsql-performance(at)postgresql(dot)org,Michael Glaesemann <grzm(at)myrealbox(dot)com>
Subject: Re: Performance analysis of plpgsql code
Date: 2005-06-28 03:03:06
Message-ID: 1119927786l.11411l.3l@mofo (view raw or flat)
Thread:
Lists: pgsql-patchespgsql-performance
On 06/27/2005 08:34:19 PM, Michael Fuhr wrote:
> On Tue, Jun 28, 2005 at 01:54:08AM +0000, Karl O. Pinc wrote:
> > On 06/27/2005 06:33:03 PM, Michael Fuhr wrote:
> >
> > >See timeofday().
> >
> > That only gives you the time at the start of the transaction,
> > so you get no indication of how long anything in the
> > transaction takes.
> 
> Did you read the documentation or try it?  Perhaps you're thinking
> of now(), current_timestamp, and friends, which don't advance during
> a transaction; but as the documentation states, "timeofday() returns
> the wall-clock time and does advance during transactions."

Very sorry.  I did not read through the complete documentation.

> I just ran tests on versions of PostgreSQL going back to 7.2.8 and
> in all of them timeofday() advanced during a transaction.

For all your work a documentation patch is appended that
I think is easier to read and might avoid this problem
in the future.  If you don't read all the way through the
current cvs version then you might think, as I did,
that timeofday() is a CURRENT_TIMESTAMP related function.

Sorry, but 3 lines wrap in the patch
in my email client.  :(


Karl <kop(at)meme(dot)com>
Free Software:  "You don't pay back, you pay forward."
                  -- Robert A. Heinlein


--- func.sgml	2005-06-26 17:05:35.000000000 -0500
+++ func.sgml.new	2005-06-27 21:51:05.301097896 -0500
@@ -5787,15 +5787,6 @@
     </para>

     <para>
-    There is also the function <function>timeofday()</function>, which  
for historical
-    reasons returns a <type>text</type> string rather than a  
<type>timestamp</type> value:
-<screen>
-SELECT timeofday();
-<lineannotation>Result: </lineannotation><computeroutput>Sat Feb 17  
19:07:32.000126 2001 EST</computeroutput>
-</screen>
-   </para>
-
-   <para>
      It is important to know that
      <function>CURRENT_TIMESTAMP</function> and related functions  
return
      the start time of the current transaction; their values do not
@@ -5803,8 +5794,7 @@
      the intent is to allow a single transaction to have a consistent
      notion of the <quote>current</quote> time, so that multiple
      modifications within the same transaction bear the same
-    time stamp. <function>timeofday()</function>
-    returns the wall-clock time and does advance during transactions.
+    time stamp.
     </para>

     <note>
@@ -5815,6 +5805,18 @@
     </note>

     <para>
+    There is also the function <function>timeofday()</function> which
+    returns the wall-clock time and advances during transactions.  For
+    historical reasons <function>timeofday()</function> returns a
+    <type>text</type> string rather than a <type>timestamp</type>
+    value:
+<screen>
+SELECT timeofday();
+<lineannotation>Result: </lineannotation><computeroutput>Sat Feb 17  
19:07:32.000126 2001 EST</computeroutput>
+</screen>
+   </para>
+
+   <para>
      All the date/time data types also accept the special literal value
      <literal>now</literal> to specify the current date and time.   
Thus,
      the following three all return the same result:


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