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2-94 IBM Informix OnLine Database Server Administrator’s Guide
OnLine Limits for Chunks
The size of each chunk entry on the chunk-tracking page is the length of the
chunk pathname plus 29 bytes. The available space on the tracking page is
BUFFSIZE minus 28 bytes. As you calculate the number of possible chunk
entries, remember that each chunk entry might require up to three additional
bytes to accommodate 4-byte alignment. In the example calculation that
follows, it is assumed that all chunk pathnames are the same size, 10 bytes,
and the page size is two kilobytes:
Each chunk pathname is 10 bytes.
Additional chunk information requires 29 bytes.
Each chunk entry requires a total of 39 bytes.
For 4-byte alignment, each chunk entry requires a total of 40
bytes.
BUFFSIZE is equal to 2 kilobytes or 2048 bytes.
Space available on the chunk-tracking page
is equal to 2048 - 28 or 2020 bytes.
The maximum number of chunk entries that can fit on the chunk-
tracking page is equal to 2020/40 or 50.
To avoid difficulties that might occur if you run out of space for chunk entries
or if you start to exceed the maximum number of available files, follow these
suggestions:
■ Select short chunk pathnames.
■ Create large chunks.
Add chunks only as needed. You can easily add chunks during OnLine
operation. However, if you over-allocate chunks to a blobspace or dbspace
when you first create it, the space remains tied up but unused. You cannot
drop or move individual chunks from a blobspace or dbspace.