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Update the ARCHITECTURE document

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Also has a pretty line diagram
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Neil Booth 2017-01-03 17:05:39 +09:00
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Components
==========
The components of the server are roughly like this::
-------
- Env -
-------
-------
- IRC -
-------
<
------------- ------------
- ElectrumX -<<<<<- LocalRPC -
------------- ------------
< >
---------- -------------------
- Daemon -<<<<<<<<- Block processor -
---------- -------------------
< < >
-------------- -----------
- Prefetcher - - FS + DB -
-------------- -----------
.. image:: https://docs.google.com/drawings/d/1Su_DR2c8__-4phm12hAzV65fL2tNm_1IhKr4XivkW6Q/pub?w=720&h=540
:target: https://docs.google.com/drawings/d/1Su_DR2c8__-4phm12hAzV65fL2tNm_1IhKr4XivkW6Q/pub?w=960&h=720
Env
---
Holds configuration taken from the environment. Handles defaults
appropriately. Generally passed to the constructor of other
components which take their settings from it.
Holds configuration taken from the environment, with apprioriate
defaulting appropriately. Generally passed to the constructor of
other components which take their settings from it.
Controller
----------
The central part of the server process initialising and coordinating
all the others. Manages resource usage.
LocalRPC
--------
Handles local JSON RPC connections querying ElectrumX server state.
Not started until the block processor has caught up with the daemon.
Started when the ElectrumX process starts.
ElectrumX
---------
Handles JSON Electrum client connections over TCP or SSL. One
instance per client session. Should be the only component concerned
with the details of the Electrum wire protocol. Responsible for
caching of client responses. Not started until the block processor
has caught up with the daemon. Logically, if not yet in practice, a
coin-specific class.
with the details of the Electrum wire protocol.
Not started until the block processor has caught up with the daemon.
Daemon
------
Used by the block processor, ElectrumX servers and prefetcher.
Encapsulates daemon RPC wire protcol. Logically, if not yet in
practice, a coin-specific class.
Encapsulates the RPC wire protcol with bitcoind for the whole server.
Transparently handles temporary daemon errors, and fails over if
necessary.
Block Processor
---------------
Responsible for managing block chain state (UTXO set, history,
transaction and undo information) and processing towards the chain
tip. Uses the caches for in-memory state updates since the last
flush. Flushes state to the storage layer. Reponsible for handling
block chain reorganisations. Once caught up maintains a
representation of daemon mempool state.
transaction and undo information) and for handling block chain
reorganisations.
Database
--------
When caught up, processes new blocks as they are found, and flushes
the updates to the database immediately.
The database. Along with the host filesystem stores flushed chain state.
When syncing uses caches for in-memory state updates since the prior
flush. Occasionally flushes state to the storage layer when caches
get large.
Prefetcher
----------
Used by the block processor to asynchronously prefetch blocks from the
daemon. Holds fetched block height. Once it has caught up
additionally obtains daemon mempool tx hashes. Serves blocks and
mempool hashes to the block processor via a queue.
Cooperates with the block processor to asynchronously prefetch blocks
from bitcoind. Once it has caught up it additionally requests mempool
transaction hashes from bitcoind. Serves blocks to the block
processor via a queue, and the mempool hashes to the Mempool object.
Mempool
-------
Handles all the details of maintaining a representation of bitcoind's
mempool state. Obtains the list of current mempool transaction hashes
from the Daemon when notified by the Prefetcher.
Notifies the controller that addresses have been touched when the
mempool refreshes (or implicitly when a new block is found).
Database
--------
The database. Flushed chain state is stored in the DB backend, such
as leveldb, along with metadata on the host filesystem.
IRC
---
Not currently imlpemented; will handle IRC communication for the
ElectrumX servers.
Handles advertising of ElectrumX services via IRC.