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Cc: pgsql-docs <pgsql-docs@postgresql.org>
Subject: Re: Improve warnings around CREATE INDEX CONCURRENTLY
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Greg Smith <greg@2ndquadrant.com>
In-reply-to: <4DDD6EC3.80703@2ndQuadrant.com>
References: <4DDB64CB.7070109@2ndQuadrant.com>
	<1306269968-sup-2890@alvh.no-ip.org>
	<4DDC1DBF.3050306@2ndQuadrant.com>
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	<4DDD6EC3.80703@2ndQuadrant.com>
Date: Thu, 26 May 2011 11:52:27 -0400
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Excerpts from Greg Smith's message of mié may 25 17:04:03 -0400 2011:

> Sure.  Simon's command string idea might work better, and doing some 
> extra lock decoration as you suggested in the above thread would be 
> another level of improvement.  We should pick up redesign later on the 
> main list.  You can at least count me in as someone who wants to see 
> this improved now.

Great

> Back to the doc patch I submitted...is that a useful step toward making 
> this issue visible enough to users for now to help?

Sure, why not?  I thought I could choose my bikeshed color while I was
here, how about

+    second and third transaction.  All active transactions at the time the
+    second table scan starts, not just ones that already involve the table,
+    have the potential to block the concurrent index creation until they
+    finish.  When checking for transactions that
+    could still use the original index, concurrent index creation advances
+    through potentially interfering older transactions one at a time,
+    obtaining shared locks on their virtual transaction identifiers to wait for
+    them to complete.


-- 
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
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