A Practical Hardware Sizing Guide for Sybase IQ

memory sizes has been covered in detail. Should that take too much time or not be feasible, the
alternative is to make an educated guess and adjust according to usage monitoring.
A rule of thumb for this educated guess is to allocate no more than two-thirds of the total RAM to
the IQ main and temporary caches. On a system with 64 GB RAM, this would mean that the
combined total of the main (-iqmc) and temporary (-iqtc) caches would consume no more than
48 GB RAM.
This will allow IQ to use a considerable amount of RAM for its operations without overburdening
the system. Since the IQ caches tend to consume 80% or more of all IQ memory, over sizing
these caches can cause severe performance issues should the OS need to swap out the memory
to disk.
Swap Space Allocation
It is generally recommended that the system swap space be set to twice the amount of RAM on
the machine. However, systems with a large amount of RAM (64 GB or more) should be able to
allocate 1x physical RAM for swap space. This should provide enough of a buffer, should
swapping begin, to allow administrators to detect and address the problem. As was pointed out
in the previous sections, IQ can allocate a considerable amount of RAM outside of the main and
temp caches (load memory, bitmap memory, and backup memory). In order to prevent a
situation where all virtual memory has been exhausted on the system, swap space should be set
to roughly twice the amount of RAM. This gives the system enough space to compensate for
unforeseen situations where the heap memory must grow beyond the physical RAM. Certainly,
this will come at the cost of performance, but the operations won‟t fail for lack of memory
(physical or virtual).
Example
For example, consider two different systems: one with 16 GB RAM and another with 32 GB RAM.
For the sake of this exercise, it is assumed that there will be five concurrent load processes and
that load memory has been set to 200 MB. It is also assumed that the loads won‟t need a
considerable amount of bitmap memory for their processing.
16 GB system 32 GB system
Operating System 1 GB 1 GB
Filesystem Cache 1 GB 2 GB
All Other Applications 500 MB 500 MB
IQ Catalog Memory 128 MB 256 MB
IQ Thread Memory 250 MB 500 MB
Load Memory 1 GB 1 GB
Bitmap Memory 256 MB 256 MB
IQ Main Cache 4.4 GB 10.4 GB
IQ Temporary Cache 6.6 GB 15.6 GB
Backup Memory N/A N/A
Total 15.125 GB 31.5 GB
Final
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