jean@beno.CSS.GOV (Jean Anderson) (10/30/90)
As a DBA I am frequently called upon to justify free space allocation--disk
space required to rollback a large transaction or to process a user's query
(temporary tables to hold the intermediate results from sorts, aggregate
counts for large datasets, etc.).
I have heard various rules of thumb. For INGRES 5 and ORACLE 5 both, I
heard that 30% of disk space should be allocated as free space. Or
twice the largest table (or joined tables) which will reported on.
--Or more depending on the number of columns in the ORDER BY clause.
Under ORACLE 6, I heard one ORACLE tech support person say that 42% of
the disk allocated should be dedicated to temporary space (space for
rollback segments, processing of user's queries, etc.). For one of our
main applications with heavy interactive querying, 40% seems to hold us at
a steady state with only occasional problems when a particularly ambitious
query hits the system.
So I guess the question is: What other "rules of thumb" are there out
there? And what strategies do folks resort to in order to convince
management that N% free really is necessary in order to provide smooth,
uninterrupted services?
- Jean Anderson
DBA, SAIC Geophysics Division
(619)458-2727
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++ Any opinions are mine, not my employer's. ++
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