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Re: crash managing a large FSFS repository

From: Simon Spero <ses_at_unc.edu>
Date: 2004-12-13 23:31:28 CET

kfogel@collab.net wrote:

>middle metric was about), we can multiply 51,236 * 8 to get 409,888.
>Nice, about half a meg. Of course, we need to add in the usual tree
>structure overhead, which is a whole hash-table per unique entry
>except for the leaf nodes. I'm not really sure how to estimate that.
>It's more than log(51,236), but less than 51,236. Plus we need a
>4-byte pointer per entry...
Regular hashtable overhead is ~ 24 bytes per node. The per node lookup
table needn't be a hash table; a binary search table may be better,
especially if the input data is mostly sorted. That could bring the
overhead down to ~4 bytes.

>So, is it really looking so much better than 9 MB, in the long run?
>I don't mean to be reflexively skeptical, but at least this back-of-the-envelope estimate doesn't look promising. Maybe I'm missing something, though?
Reflexive skepticism is what keeps us alive :) There may also be
interactions with the pool allocator; I do think that path length
explains at least 25% of the memory growth. I think it's time to run a
profiler and see where the memory is going (but that spoils the fun).

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Received on Mon Dec 13 23:39:33 2004

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