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From Lin Ma <lin...@gmail.com>
Subject how client location a region/tablet?
Date Sat, 18 Aug 2012 09:13:37 GMT
Hello guys,

I am referencing the Big Table paper about how a client locates a tablet.
In section 5.1 Tablet location, it is mentioned that client will cache all
tablet locations, I think it means client will cache root tablet in
METADATA table, and all other tablets in METADATA table (which means client
cache the whole METADATA table?). My question is, whether HBase implements
in the same or similar way? My concern or confusion is, supposing each
tablet or region file is 128M bytes, it will be very huge space (i.e.
memory footprint) for each client to cache all tablets or region files of
METADATA table. Is it doable or feasible in real HBase clusters? Thanks.

BTW: another confusion from me is in the paper of Big Table section 5.1
Tablet location, it is mentioned that "If the client’s cache is stale, the
location algorithm could take up to six round-trips, because stale cache
entries are only discovered upon misses (assuming that METADATA tablets do
not move very frequently).", I do not know how the 6 times round trip time
is calculated, if anyone could answer this puzzle, it will be great. :-)

have a good weekend,
Lin

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