Getting the Best
Performance from V9
Threaded PROC SORT
Scott Mebust
System Developer
Base Information Technology
Copyright © 2005, SAS Institute Inc. All rights reserved.
The (Unofficial) SAS Skydiving Team
Copyright © 2005, SAS Institute Inc. All rights reserved.
2
Keys to Sorting Performance




Know the conditions
Observe actual performance
Understand theoretical performance
Make adjustments
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3
Know the Conditions
 System
 SAS
 Sort job
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4
Observe Actual Performance
 Monitor System Activity
 Examine the SAS Log
 Measure System Capabilities
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8
Identify and Observe Sorting Phases
I/O Bound, External, Single-Threaded
Sort Phase
Merge Phase
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9
Measure Storage Device Sequential
Transfer Rates From Within SAS




Create a large dataset (e.g. 4xRAM)
Read dataset, dumping to _NULL_
Ensure Real time » CPU time
Compute transfer rates (R)
Rread 
F
Rwrite 
tread
F
twrite
Where
F: size of the dataset (bytes)
t: real time (seconds)
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12
Measure In-Core Sorting Costs
CPU Time Per Observation
5.00E-07
Normalized CPU Time
(seconds)
4.50E-07
4.00E-07
Small job
overhead
3.50E-07
3.00E-07
Actual
2.50E-07
Predicted
2.00E-07
1.50E-07
1.00E-07
5.00E-08
0.00E+00
10000
100000
1000000 10000000
1E+08
Number of Observations
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14
Understand Theoretical Performance
 Classify the job
 Estimate SORT running time
 Consider estimation hazards
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15
Classify the Job Performance Limitation
 Compute Bound
 I/O Bound
 Mixed
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16
Classify the Job Size
 F O 
 1  Internal

 M

 F O

 1  External

 M




B  F  O  M  SinglePass

B  F  O  M  MultiPass
Where
F: size of input dataset
O: size of internal sorting overhead
M: size of RAM
B: utility file page (block) size
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17
Estimate the Running Time
Internal Sort, I/O Bound
F
tread 
Rread
Input Sequential Read
t  tread  twrite
RAM
Output
Where
t: real time (sec)
F: dataset size (bytes)
R: transfer rate (bytes/sec)
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Sequential Write
F
twrite 
Rwrite
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Estimate the Running Time
Single-Pass External, I/O Bound
Input Sequential Read
RAM
F
t1 
Rread
Sequential Write
U
t2 
Rwrite
t  t1  t 2  t 3  t 4
Temp
F
t4 
Rwrite
Output
Sequential Write
t3  ?
RAM
Random Read
Where U: utility file size (bytes)
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22
Utility File Read Time
File Size
Single-threaded:
Multi-threaded:
U  F o
UF
Number of Pages
U 
npages   
B
where
F: size of input dataset
o: # of observations × sort key length
where
B: utility file page (block) size
Best Case (Sequential) Read Time
Worst Case (Random) Read Time
U
tread 
Rread
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B 

tread  npages   s  r  

Rread 

where
s: average positional latency
r: average rotational latency
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Multi-Pass External Sorting
Number of Sorted Runs
Number of Utility File Passes
F O
nruns  
 M 
 Ln(nruns) 
npasses  

Ln
(
n
buffers
)


where
M 
nbuffers   
B
is the
Maximum External
Merge Order
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and
F: size of input dataset
O: size of internal sorting overhead
M: SORTSIZE
B: utility file page (block) size
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Estimate the Running Time
Single-Pass External, Compute Bound
Input
RAM
tsort  ?
t  tsort  tmerge  twrite
Temp
F
twrite 
Rwrite
Output
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Sequential Write
tmerge  ?
RAM
Random Read
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Single-Pass External, Compute Bound
Utility File Creation Time
tsort  nruns  trun
Utility File Merge Time, Compute Bound
tmerge  tsort
where
F O
nruns  
 M 
trun is the time required to perform an
in-memory sort the number of
observations in a single run
Utility File Merge Time, I/O Bound
Best Case:
U
tmerge 
Rread
Worst Case:
 nobs 
runobs  
 nruns 
B 

tmerge  npages   s  r  

Rread 

Where nobs is the total number of
observations in the dataset
As previously described for
I/O bound Utility File Read Time
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26
Consider Estimation Hazards




File cache effects
Pseudo-internal sorting (thrashing)
Pseudo-external sorting (file cache)
Limitations within each sorting phase
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27
Make adjustments




Determine if there is a problem
Identify the problem
Alter the conditions
Re-evaluate
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30
Identify the Problem
 Processing speed
 Memory
 External Storage
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31
Alter the Conditions




Memory settings
Library to storage device mappings
Utility file location
Utility file page size
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