On Jan 17, 2008, at 3:26 PM, Pete Wyckoff wrote:
I just noticed this bit in trove-dbpf/dbpf.h. The code carefully
builds ((<collid> << 24) | <handleid>) then does a modulo against
a power of 2, effectively stripping off all but the low bits of
the handleid.
The collid is not used in the hash at all. Just in case anybody
thought this was important. I've ever only used one collection per
server.
Hi Pete,
KEYVAL_GET_BUCKET is left over from the days when we did a keyval DB
per file. With just one keyval DB now, we don't use that macro --
there's no where in the code it gets called -- so you could safely
remove it if you want.
As for BSTREAM_GET_BUCKET, that's funny that the coll-id isn't used in
the hash, but it turns out not to matter. The buckets end up as
directories that allow us to keep the bstream directories smaller, but
here too, all those directories are within a directory for the entire
collection. Go ahead and pull out the coll_id bits of the hash if you
want.
-sam
-- Pete
/*
for more efficient host filesystem accesses, we have a simple
*_MAX_NUM_BUCKETS define that can be thought of more or less as
buckets for storing bstreams based on a simple hash of the unique
handle/coll_id combination.
in practice, this means we spread all bstreams into
*_MAX_NUM_BUCKETS directories instead of keeping all bstream entries
in a flat bstream directory on the host filesystem.
*/
#define DBPF_KEYVAL_MAX_NUM_BUCKETS 32
#define DBPF_BSTREAM_MAX_NUM_BUCKETS 64
#define DBPF_KEYVAL_GET_BUCKET(__handle,
__id) \
(((__id << ((sizeof(__id) - 1) * 8)) | __handle)
% \
DBPF_KEYVAL_MAX_NUM_BUCKETS)
#define DBPF_BSTREAM_GET_BUCKET(__handle,
__id) \
(((__id << ((sizeof(__id) - 1) * 8)) | __handle)
% \
DBPF_BSTREAM_MAX_NUM_BUCKETS)
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