ExternalVendorCode/tahoe-lafs
1
0
Fork 0
mirror of https://github.com/tahoe-lafs/tahoe-lafs.git synced 2024-12-24 07:06:41 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

Update 'docs/architecture.txt' to reflect readonly share discovery

Browse Source
This commit is contained in:
kevan 2010-05-13 17:38:52 -07:00
parent 98325b40ee
commit 1338318644
1 changed files with 13 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
docs/architecture.txt
View File

@ -146,14 +146,20 @@ In the current version, the storage index is used to consistently-permute the
set of all peer nodes (by sorting the peer nodes by set of all peer nodes (by sorting the peer nodes by
HASH(storage_index+peerid)). Each file gets a different permutation, which HASH(storage_index+peerid)). Each file gets a different permutation, which
(on average) will evenly distribute shares among the grid and avoid hotspots. (on average) will evenly distribute shares among the grid and avoid hotspots.
We first remove any peer nodes that cannot hold an encoded share for our file,
and then ask some of the peers that we have removed if they are already
holding encoded shares for our file; we use this information later. This step
helps conserve space, time, and bandwidth by making the upload process less
likely to upload encoded shares that already exist.
We use this permuted list of nodes to ask each node, in turn, if it will hold We then use this permuted list of nodes to ask each node, in turn, if it will
a share for us, by sending an 'allocate_buckets() query' to each one. Some hold a share for us, by sending an 'allocate_buckets() query' to each one.
will say yes, others (those who are full) will say no: when a node refuses Some will say yes, others (those who have become full since the start of peer
our request, we just take that share to the next node on the list. We keep selection) will say no: when a node refuses our request, we just take that
going until we run out of shares to place. At the end of the process, we'll share to the next node on the list. We keep going until we run out of shares
have a table that maps each share number to a node, and then we can begin the to place. At the end of the process, we'll have a table that maps each share
encode+push phase, using the table to decide where each share should be sent. number to a node, and then we can begin the encode+push phase, using the table
to decide where each share should be sent.
Most of the time, this will result in one share per node, which gives us Most of the time, this will result in one share per node, which gives us
maximum reliability (since it disperses the failures as widely as possible). maximum reliability (since it disperses the failures as widely as possible).