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Date:         Sun, 29 Jan 2006 07:46:56 -0500
Reply-To:     "Richard A. DeVenezia" <rdevenezia@WILDBLUE.NET>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Richard A. DeVenezia" <rdevenezia@WILDBLUE.NET>
Subject:      Re: What is maximum number of variables allowed
Comments: To: sas-l@uga.edu

David L Cassell wrote: > art297@NETSCAPE.NET replied: >> Then I was even more surprised that 2 million worked after having >> failed previously. >> >> Then, I was totally confused when SAS9 failed with 2097150 and >> returned the message that the maximum allowed for the file was >> 16777191. >> >> I would think that someone from SAS needs to respond regarding what >> the actual number is. > > I don't think there *is* a fixed number. > > I think that your work, as well as other experiments around here, are > demonstrating > that this is memory-dependent. Which could mean that - as your OS > adjusts the > amount of memory available to the SAS system - you may continue to get > fluctuating > results. > > Of course, I'm probably wrong. But it seems clear that the number of > variables > (and the length of the PDV created by that number of variables) is > going to be > memory-dependent. > > But larger than we usually work with... > > David

16777191

Interestingly 16,777,191 is 2**24.

A row with 2**24 numeric variables (double precision reals) of length 8 requires 2**27 bytes of storage/working space, plus overhead and alignment issues (if any)

One speculation is that internally 32-bit positive integers (31 if signed) are used to index into the memory buffer of a row, or at least index into a hash mapping to the address of a variable -- this would indicate the maximum allocation of a rows internal buffer is 4GB (2**32) or 2GB (2**31).

There is a 2**4 factor ratio between 2**31 and 2**27. This might indicate the internal scheme for dealing with a single wide row is perhaps utilizing a paging algorithm that requires adding 16 bytes to each variable to make it's value locatable in the working space.

Richard A. DeVenezia http://www.devenezia.com/


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