[SNMP4J] TableUtils - more efficient fetching of sparse tables

[Frank Fock]

Hi Michal,
The proposed improvement can be indeed applied to any column,
but will have an effect only if the a lot of cells are missing and the distribution is asymmetric.
I will try to implement the improvement for SNMP4J 2.4.0

Best regards
Frank

> Am 02.12.2015 um 09:19 schrieb Michał Steiner <mist at mist.pl>:
> 
> Hi,
> 
> I've noticed that getTable method in org.snmp4j.util.TableUtils could be
> more efficient for sparse tables.
> 
> Consider table with 3 columns and 3 rows, but in first column there is a
> lot of empty cells:
> 
> Column1           Column2        Column3
> value-1-1         value-2-1     value-3-1
> <empty>           value-2-2     value-3-2
> <empty>           value-2-3     value-3-3
> 
> Today implementation works more or less like this:
> 
> get-next   Column1      Column2       Column3
> response   value-1-1    value-2-1     value-3-1
> 
> get-next   value-1-1      value-2-1     value-3-1
> response   value-2-1      value-2-2     value-3-2
> 
> get-next   value-1-1       value-2-2     value-3-2
> response   value-2-1       value-2-3     value-3-3
> 
> get-next   value-1-1      value-2-3     value-3-3
> response   value-2-1      value-3-3     value from next table
> 
> 
> As you can see  request for    value-1-1  is done 3 times and only first
> one makes sense.
> This is  an issue for large tables (lot of columns and rows) with many
> empty cells.
> This algorithm can be improved. After first response from other column we
> can just stop asking about it. Conversation will look like this:
> 
> 
> get-next    Column1    Column2        Column3
> response   value-1-1   value-2-1      value-3-1
> 
> get-next   value-1-1    value-2-1     value-3-1
> response   value-2-1    value-2-2     value-3-2    <-- value-2-1  is from
> different column
> 
> get-next               value-2-2      value-3-2 <-- in next requests we
> skip  first column
> response               value-2-3      value-3-3
> 
> get-next               value-2-3      value-3-3
> response               value-3-3      value from next table
> 
> I guess that bulk request are handled in the similar way, aren't they ?
> 
> Are my observations correct ?
> What do you think about such improvement?
> 
> 
> Regards
> 
> Michal
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