Differences

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--- pracro:database [2008/11/25 09:00] – created deva
+++ pracro:database [2010/06/03 16:33] – deva
@@ Line 1: / Line 1: @@
 ======Pracro Database design======
-Nothing to see here, move along....
+Nothing to see here, move along...
+=====Persistent transactions=====
+When a new Pracro session is initiated, a connection to PostgreSQL is made.
+All commands (strings) issued to this connection, will be appended to a string contained in the session class.
+This string will be serialised with the rest of the session data upon pracrod shutdown and re-read on startup.
+The first SQL command issued is BEGIN;
+If a 'commit' is received by the pracro server, it is translated into a COMMIT; on the SQL connection and the command string is cleared.
+If the clienbt disconnects without any actions, an ROLLBACK; is sent to the SQL server.
+On reconnect to the session, the entire command string is replayed as it is, and the session is ready to continue where it left off.
+On the pracro 'discard' command, a ROLLBACK; is sent to the SQL server, and the command string is cleared.
+====Sequence numbers====
+All sequence numbers must be obtained from a seperate SQL conenction, that is not affected by the SQL transactions. It is vital that these numbers are not reused in later sessions.
+All sequence numbers used in the pracro sessions must therefor be used as strings, directly in the syntax strings.
+<code>
+global Db1
+getSeq()
+{
+  Mutex.lock
+  s = Db1.exec("currval('trseq')");
+  Mutex.unlock
+  return s;
+}
+do_something
+{
+   Db2
+   Db2.exec("BEGIN");
+   Db2.exec("INSERT INTO fields VALUES('foo', 'bar','"+getSeq()+"')");
+}
+</code>