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Re: [Gluster-devel] One Question about DHT

From: Pavan T C
Subject: Re: [Gluster-devel] One Question about DHT
Date: Wed, 17 Aug 2011 15:08:27 +0530
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10

On Wednesday 17 August 2011 09:18 AM, Daniel wrote:
Hello Pavan,

I came cross one question about DHT lookup.

When dht_lookup process a fresh lookup, if the looked up target can not
be found by hashed, why does it assert it as a directory and lookup on
all the child nodes?

Not sure why you thought I should be the one to address this to. There are more knowledgeable engineers on this user group :)

I looked up the code a bit to answer your question and here is what I understand:

If it is a fresh lookup and the file hash computed for this entity did not fall into any of the pre-computed hashed ranges, a lookup_everywhere is triggered to go to the backend and see if it exists there. If it is not there too, this brings in a mechanism called "directory self heal".

The debug message does say - "see if it is a directory", but if you look at the dht_lookup_dir_cbk, a check is also made to see if it was *not* a directory. It might only be the debug messages that might have led you into thinking why a directory is being looked up in particular. That is not really the case.




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