Add README

Author: okumin

README.md

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+# akka-persistence-sql-async
+
+A journal and snapshot store plugin for [akka-persistence](http://doc.akka.io/docs/akka/2.3.6/scala/persistence.html) using RDBMS.
+Akka-persistence-sql-async executes queries by [ScalikeJDBC-Async](https://github.com/scalikejdbc/scalikejdbc-async) that provides non-blocking APIs to talk to databases.
+
+
+Akka-persistence-sql-async supports following databases.
+- MySQL
+- PostgreSQL
+
+## Usage
+
+In application.conf,
+
+```
+akka {
+  persistence {
+    journal.plugin = "akka-persistence-sql-async.journal"
+    snapshot-store.plugin = "akka-persistence-sql-async.snapshot-store"
+
+    # disable leveldb (default store impl)
+    journal.leveldb.native = off
+  }
+}
+
+akka-persistence-sql-async {
+  journal.class = "akka.persistence.journal.sqlasync.MySQLAsyncWriteJournal"
+  snapshot-store.class = "akka.persistence.snapshot.sqlasync.MySQLSnapshotStore"
+  
+  # For PostgreSQL
+  # journal.class = "akka.persistence.journal.sqlasync.PostgreSQLAsyncWriteJournal"
+  # snapshot-store.class = "akka.persistence.snapshot.sqlasync.PostgreSQLSnapshotStore"
+
+  user = "root"
+  pass = ""
+  url = "jdbc:mysql://localhost/akka_persistence_sql_async"
+  max-pool-size = 4
+  journal-table-name = "journal"
+  snapshot-table-name = "snapshot"
+}
+```
+
+## Table schema
+
+Create the database and tables for journal and snapshot store.
+
+### MySQL
+
+```
+CREATE TABLE IF NOT EXISTS {your_journal_table_name} (
+  persistence_id VARCHAR(255) NOT NULL,
+  sequence_nr BIGINT NOT NULL,
+  marker VARCHAR(255) NOT NULL,
+  message BLOB NOT NULL,
+  created_at TIMESTAMP NOT NULL,
+  PRIMARY KEY (persistence_id, sequence_nr)
+);
+
+CREATE TABLE IF NOT EXISTS {your_snapshot_table_name} (
+  persistence_id VARCHAR(255) NOT NULL,
+  sequence_nr BIGINT NOT NULL,
+  created_at BIGINT NOT NULL,
+  snapshot BLOB NOT NULL,
+  PRIMARY KEY (persistence_id, sequence_nr)
+);
+```
+
+### PostgreSQL
+
+```
+CREATE TABLE IF NOT EXISTS {your_journal_table_name} (
+  persistence_id VARCHAR(255) NOT NULL,
+  sequence_nr BIGINT NOT NULL,
+  marker VARCHAR(255) NOT NULL,
+  message BYTEA NOT NULL,
+  created_at TIMESTAMP NOT NULL,
+  PRIMARY KEY (persistence_id, sequence_nr)
+);
+
+
+CREATE TABLE IF NOT EXISTS {your_snapshot_table_name} (
+  persistence_id VARCHAR(255) NOT NULL,
+  sequence_nr BIGINT NOT NULL,
+  created_at BIGINT NOT NULL,
+  snapshot BYTEA NOT NULL,
+  PRIMARY KEY (persistence_id, sequence_nr)
+);
+```
+
+## License
+
+Apache 2.0