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Re: system table scan

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Ehab Galal" <ehabgalal123(at)hotmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: system table scan
Date: 2006-11-27 05:21:53
Message-ID: 2957.1164604913@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Ehab Galal" <ehabgalal123(at)hotmail(dot)com> writes:
> If i understand correctly, i may use systable_beginscan() and 
> systable_getnext() to scan a system table while specifying a key (e.g., 
> username='user1'). But i know nothing about specifying the order of the 
> scan.

The systable_xxx functions allow implementation by either indexscan or
seqscan, therefore they guarantee *nothing* about retrieval order.

If your code does not need to be executed during bootstrap or crash
recovery, you could depend on an indexscan instead.  See
toast_fetch_datum() for an example.

			regards, tom lane

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