Naming. Sandhya Turaga CS-249 Fall-2005. Outline of Chapter. Naming in general Characteristics of distributed naming Bindings Consistency Scaling Approaches to Design a global name service DEC Global Name Service ( by Lampson)
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Never reused, always bound to an object, &provides location independence
Nothing but a bit pattern that is an identifier
Pure names commit one to nothing –
Carries commitments of one sort or the another
Machine to address binding
Services to machine binding
How one propagates updates among replicates of a naming database (Explained more in the DEC example)
Being able to manage indefinite number of machines each providing some part of name lookup service of indefinite size which is managed by a great number of more or less autonomous administrators without any major changes to the existing environment.
Managing name Space rather than the avoidance of scale disasters In the implementation
In the figure1 finance/personal is relative to root src
add a new root by making the existing root nodes as its children (Figure 6).
1) Slow rate of change on the naming database
2) Or Tolerating some inaccuracy in caching data
expiration time (TX) on entries in the database with an exception.
Valid until 20 Nov 2006
m- Manager identifier
S-Specific directory identifier
when a cache search returns a cache entry containing the name of the managerial directory it is called “Hit”
When a cache search doesn’t return the name of the directory but does return something is called near miss.
1) High cache-hit ratio & Performance.
2) Near miss reduces the amount of work required for the shared naming system.
3) The longer the prefix returned by the near miss the more work is saved.
4) Correctness of cache information is automatically checked.
( see figure 12)
1) A packet event is transmission or reception of network packet.
2) Multicast with g recipients costs g+1pkt events
3)The avg number of pkt events required to map an event
Cmap=4h + (r + m + 7)(1 - h)
when there is cache hit name mapping costs -4 pkt events
when there is a cache miss r+m+7pkt events
1) No.of name-mapping requests issued per unit time
2) The average length of time a name-cache entry is valid
3)The average length of time a client cache remains in use before it is discarded
4)The locality of reference
h=1-∑ ∑ ß/( ßj,k +vk )
ßj,k –Avg interarrival time for requests generated by client j that reference a name in managerial sub tree k.
Vk –Validity time for cache entry of a managerial sub tree k.
ß-Global Avg interarrival time for name-mapping requests.
hj,k =1- ßj,k /( ßj,k +vk )
in the range 99.00-99.98?
client, sub tree pair
Depends on validity time
( see figures 15 )
( see figure 16 )