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+# wsrep API node application
+
+## Overview
+
+This is a simple application to demonstrate the usage of wsrep API. It
+deliberately does nothing useful in order to present as concentrated and
+concise API usage as possible.
+
+The program is deliberately written in C to demonstrate the naked API usage.
+For C++ example see a much more advanced integration library at
+https://github.com/codership/wsrep-lib
+
+## High level architecture
+
+Process-wise the program consists of an endless main loop that periodically
+samples and prints performance stats and a configurable number of "master" and
+"slave" threads, with master threads loop executing "transactions" and
+replicating resulting "write sets" and slave threads receiving and processing
+the write sets from other nodes.
+
+Object-wise the program is composed of two main objects: `store` and `wsrep`.
+'store' object contains application "state" and generates and commits changes
+to the state. `wsrep` object contains cluster context and provides interface
+to it. Changes generated by `store` are replicated and certified through
+`wsrep` and then committed to `store`.
+
+## Unit descriptions (in alphabetical order)
+
+#### ctx.h
+A small header to declare the application context structure.
+
+#### log.*
+Implements logging functionality for the application AND
+**a logging callback** for the wsrep provider.
+
+#### main.c
+Defines `main()` routine that initializes storage and wsrep provider, starts
+the worker threads and loops in a statistics collection loop. Even though it is
+not designed to return it still shows the deinitialization order.
+
+#### options.*
+Implements reading configuration options from the command line, does not have
+anything related to wsrep API, but shows which additional parameters must be
+configured for the program to make use of wsrep clustering.
+
+#### socket.*
+Network sockets boilerplate code for setting TCP connections between processes
+(for SST). Has nothing wsrep-related and can be ignored.
+
+#### sst.*
+Defines **SST callbacks** for the wsrep provider and shows how to asynchronously
+implement state snapshot transfer (yes, you don't want to spend eternity in
+callbacks).
+
+#### stats.*
+Implements performance stats collecting function for the main loop. While it is
+an absolutely optional provider functionality, still it shows how to use that.
+
+#### store.*
+Defines the `store` object that pretends to store and modify some data in a
+"transactional" manner. It provides the caller that intends to do a change with
+a *change data* and a *key* for replication and certification.
+
+#### trx.*
+Defines routines to process local and replicated transactions.
+
+#### worker.*
+Implements worker thread pool functinality. Worker threads run routines defined
+in 'trx.*'. Also implements **apply callback** for the wsrep provider.
+
+#### wsrep.*
+Maintains wsrep cluster context: provider instance and cluster membership view.
+While there is little use for the latter in this primitive application, still
+it shows **connected and view callbacks** usage. But mostly, for this
+application its purpose is to initialize the provider, connect to the cluster
+and offer access to initialized provider for other parts of the program.
+
+## Example usage
+```
+./node -f /tmp/galera/0 -v /tmp/galera/0/galera/lib/libgalera_smm.so -o 'pc.weight=2;evs.send_window=2;evs.user_send_window=1;gcache.recover=no' -s 8 -m 16
+```