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Dev Docs: Corrections to IBD Suggested By Saivann (Thanks!)

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David A. Harding 2015-01-31 16:12:57 -05:00
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_includes/guide_p2p_network.md
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@ -210,9 +210,9 @@ the sync node in the `getdata` message illustrated below.
![First GetData Message Sent During IBD](/img/dev/en-ibd-getdata.svg) ![First GetData Message Sent During IBD](/img/dev/en-ibd-getdata.svg)
It's important to headers-first nodes that the blocks be requested and It's important to blocks-first nodes that the blocks be requested and
sent in order because each block header references the header hash of sent in order because each block header references the header hash of
the preceeding block. That means the IBD node can't fully validate a the preceding block. That means the IBD node can't fully validate a
block until its parent block has been received. Blocks that can't be block until its parent block has been received. Blocks that can't be
validated because their parents haven't been received are called orphan validated because their parents haven't been received are called orphan
blocks; a subsection below describes them in more detail. blocks; a subsection below describes them in more detail.
@ -234,20 +234,14 @@ below:
![Second GetBlocks Message Sent During IBD](/img/dev/en-ibd-getblocks2.svg) ![Second GetBlocks Message Sent During IBD](/img/dev/en-ibd-getblocks2.svg)
Upon receipt of the second `getblocks` message, the sync node takes the Upon receipt of the second `getblocks` message, the sync node searches
first listed header hash and searches its local best block chain for a its local best block chain for a block that matches one of the header
block with that header hash. If it finds a block with that hash, it hashes in the message, trying each hash in the order they were received.
replies with 500 block inventories starting with the following block. If it finds a matching hash, it replies with 500 block inventories
But if it doesn't find a block with that hash, it takes the next header starting with the next block from that point. But if there is no
hash from the `getblocks` message and searches its block chain for that matching hash (besides the stopping hash), it assumes the only block the
hash. If that hash matches, it will reply with 500 block inventories two nodes have in common is block 0 and so it sends an `inv` starting with
starting with the following hash from that point. But, again, if it block 1 (the same `inv` message seen several illustrations above).
doesn't find that hash, it will proceed to check the next hash in the
message (and so on until it runs out of hashes in the message). If the
last hash in the message (besides the stopping hash) doesn't match, it
assumes the only block the two nodes have in common is block 0 and so it
sends an `inv` starting with block 1 (the same `inv` message seen
several illustrations above).
This repeated search allows the sync node to send useful inventories even if This repeated search allows the sync node to send useful inventories even if
the IBD node's local block chain forked from the sync node's local block the IBD node's local block chain forked from the sync node's local block