No, differently from table access, index access
doesn't require reading of index segment header. The query reads the root block
directly. Root block address is probably gotten from IND$ table columns file#
and block#+1. The block# represents index segment header location in a datafile,
root block is always next to index segment header block, even when root block
split occurs.
Jacques provided some great suggestions already
(about monitoring index tablespace read/write ratio), so monitoring buffer cache
should be done as a last resort IMHO. Monitoring only for existence
of index root block in cache wouldn't be good enough anyway, I'd check
for touch count and last touch time too (TCH and TIM columns in x$bh), but
again, as Joze pointed out nicely, these blocks can get to cache because of
updates... So no luck in tracking indexes from there :)
Tanel.
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