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Encina

History

Encina was originally developed as an experimental Transaction Processing Monitor (TPM) at Carnegie Mellon University, the commercial sponsors being IBM. Camelot, as it was known, used Mach Operating System Remote Procedure Calls (RPC)s which it made Transactional. Camelot built on earlier work known as the TABS project and even earlier academic projects such as Argus [Liskov]. Camelot had its own programming language, which was somewhat object orientated and contained the notion of persistence. Encina, by now built upon DCE, went commercial with its Academic mentors, chiefly Alfred Spector as Transarc in 1991. Transarc eventually became a wholly owned subsidiary of IBM and IBM renamed it "IBM Pittsburgh". In 2002 IBM shut this down and in time the Transarc Domain name was eventually transfered to an adult-content web-site. Encina itself continued as part of the TXSeries offering until version 6 of that product when the API was withdrawn. Transarc's DCE support (required by Encina) continued under the IBM banner until 2007, when it was formally withdrawn. Encina support continued, but only to existing customers with the appropriate contract. It was completely out-of-support by 2009.

General Description

Encina had a concept of Cell which is not to be confused with a DCE cell, in which the Encina cell is encompassed. The Encina Cell is the largest unit configurable via the DCE cell which Encina knows about (without resorting to gateways). In this Encina is like Tuxedo, and its Bulletin Board, except Encina Cells are arguably more scalable.

Encina was a client/server system, with clients making requests of servers. They do this by using the DCE RPC (Remote Procedure Call) mechanism which Encina extends with Transactions. RPCs require a vote in two phase commit policy too.

Encina is multi-threaded. A single Encina server process, called a Processing Agent (PA) can process several client requests at once. The programmer has to be dextrous in the use of multi-threaded programming and the special locks known as a "MUTEX" which allow several threads access to a single memory model. In this respect Encina has several constructs which make this task easier (for example, cofor). Several single threaded PAs can of course be started at once and are managed by the Encina system in much the same way as Tuxedo and Top End.

More Information

Information on Encina use was to be found on IBM's somewhat spartan TXSeries web-site but has now gone. There is also historical and educational interest in the book on Camelot and Avelon [Eppinger, Mummert & Spector], one of a number of books on OLTP.

Example Code for Encina

Remember the Source Code caveats.

Found in the client ...

        inFunction ("my_prog");

        mon_InitClient ("my_prog", "/.:/cellname");

        transaction {
                debit_credit (delta, remote_account);        

                exec sql select amount from dosh_on_local_database 
                        into :amount
                        where 
                        account = :local_account;

                if (amount - delta < 0) 
                        abort ("cant go overdrawn!");

                exec sql update dosh_on_local_database 
                        set amount = amount - :delta 
                        where 
                        account = :local_account and 
                        amount = :amount;

        } onAbort {
                printf ("Sorry, couldn't do it $s\n", abortReason ());
        } /* onAbort */

        mon_ExitClient (0);

A language Transarc called Transactional C was used, which is actually a collection of 'C' macros. The Transactions are bracketed with special keywords transaction, onAbort and onCommit (not shown). We can prematurely mark a Transaction as a failure using abort, which is not to be confused with the UNIX function call of the same name. In the example we don't want to go overdrawn and this is how the Transaction is marked a failure by the user. The remote work is done by a function debit_credit, the function, although it looks local is actually an Remote Procedure Call (RPC) whose interface is defined by code in an Interface Definition Language (IDL). Encina is based on DCE which provides the RPCs and the IDL. Encina's RPC and IDL are, however, given some extensions to make them Transactional. As a Transactional RPC debit_credit also has a vote in the two phase commit. Should the transaction be marked as a failure then the transaction here in the client will fail too and the entire Transaction (client and server) will be rolled back. The update will not be made. The onAbort is mandatory to allow reporting of failures.

The client, which as we can see has the Transaction control calls the debit_credit Transactional RPC ...

        void debit_credit (idl_char delta[], 
                idl_char remote_account[])
        {
                inFunction ("debit_credit");

                exec sql select amount from dosh_on_remote_database
                        into :amount
                        where
                        account = :remote_account;

                if (amount + buf->delta) < 0) 
                        abort ("can't go overdrawn!");

                exec sql update dosh_on_remote_database
                        set amount = amount + :delta
                        where
                        account = :remote_account and 
                        amount = :amount;
                
        } /* debit_credit */

As far as the SQL is concerned the server is much like the client. Note how the call abort is used to mark a Transaction as being failed (the default we assume is success). The function abortReason will actually return an indication of this, although there are more complicated and efficient ways of doing this.

Encina's Name

Although there was no solid documentation it was understood that "Encina" stands roughly for "Enterprise Network Computing in a New Era". We now stand corrected. An old Encina hand, Jim Troester councils, with some authority, that the name was derived from the Encina quarter of the Standford University campus, and that name for a large Holly Oak that is still there. Jim was a confederate of Jeff Eppinger who taught at Standford and apparently had fond memories of it. "Encina" does mean "Oak" in Castilian Spanish, although the oak referred to is generally the more Mediterranean ever-green Holly Oak (Quercus Ilex), rather than it's more northerly counterpart (Q. Robur). This results in a number of places and family names called "Encina". See questions on ZOIS's name for more examples of this type of inadvertent name overloading.

~Z~


$Date: 2014/09/10 12:14:40 $


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