A Practical Hardware Sizing Guide for Sybase IQ

size of a page. As the page size increases, so does the block size. A data page of 128KB may
compress to a single 8KB block. A 256KB page with the same data on it will consume 16KB on
disk.
Memory use won't increase or decrease as the page size is changed, per se, as the main and
temporary caches are still the same size. If the memory that IQ can reference in its caches isn't
increased, though, performance may suffer.
A system with just a handful of users will, more than likely, not experience as many issues
related to undersized memory as those environments with a lot of concurrent users.
As concurrency increases, the number of pages that are in use will increase in both main and
temporary cache. When moving to a larger page size (for instance, doubling from 128 KB page
to 256 KB page) the number of pages that can be stored in the same amount of RAM is cut in
half.
If a user is referencing a fraction of the data on a page more pages will need to be brought in to
handle the query. Should the amount of RAM dedicated to the caches not be increased, a
burden will be added to the system that can force pages that are the least recently used to be
flushed out to disk before the new data can be brought into RAM. To properly handle the same
number of users with a doubled page size, it is possible that the IQ cache sizes need to be
doubled in size.
Should the page size be changed solely on the number of rows in the table, memory contention
and a possible increase in disk activity can follow. Typically, systems with larger objects have
more memory available and thus don‟t suffer from the impacts. If the RAM sizes don‟t change
over time and the tables are expected to grow to the point where the rowcount sizing would
force a larger page size, it is recommended that the page size increase be thought through as
possibly disregarded.
Versioning is one aspect that is often overlooked as it relates to page sizes. The number of
pages needed to track versions won't change; it is the amount of cache or disk that would
increase. If one were to double the page size, the amount of cache or storage needed for
versions would also double.
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