From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM autolearn=unavailable autolearn_force=no version=3.4.4 X-Received: by 10.140.234.3 with SMTP id f3mr24227025qhc.5.1462835707115; Mon, 09 May 2016 16:15:07 -0700 (PDT) X-Received: by 10.157.8.54 with SMTP id 51mr338812oty.13.1462835707073; Mon, 09 May 2016 16:15:07 -0700 (PDT) Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!news.glorb.com!88no3220264qga.1!news-out.google.com!z2ni372itc.0!nntp.google.com!i5no6490099ige.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail Newsgroups: comp.lang.ada Date: Mon, 9 May 2016 16:15:06 -0700 (PDT) In-Reply-To: Complaints-To: groups-abuse@google.com Injection-Info: glegroupsg2000goo.googlegroups.com; posting-host=2601:191:8202:8510:5985:2c17:9409:aa9c; posting-account=fdRd8woAAADTIlxCu9FgvDrUK4wPzvy3 NNTP-Posting-Host: 2601:191:8202:8510:5985:2c17:9409:aa9c References: <9e93195a-eba0-4793-a64c-a24613090b3c@googlegroups.com> <95d6e489-463b-484b-b67e-8d37812f6b11@googlegroups.com> User-Agent: G2/1.0 MIME-Version: 1.0 Message-ID: Subject: Re: Two-stage suspend operations From: rieachus@comcast.net Injection-Date: Mon, 09 May 2016 23:15:07 +0000 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Xref: news.eternal-september.org comp.lang.ada:30366 Date: 2016-05-09T16:15:06-07:00 List-Id: On Monday, May 9, 2016 at 4:56:15 AM UTC-4, Simon Wright wrote: > I see what you mean. It's just that the wording in the ARM made it sound > as though "two-stage suspend operations" was a phrase widely known in > the community, which clearly isn't the case. If you look at this article from Wikipedia: https://en.wikipedia.org/wiki/T= wo-phase_locking and go down to "strong strict two-phase locking" you will= see that it is not you, me or the Ada Rationale. There are a lot of incon= sistent names floating around in this area, and the Rationale apparently ch= ose one that lost out. (Strong strict two-phase locking may not interest yo= u, I just picked the article as one showing considerable name confusion in = 2011.) I'm curious as to why you are interested in this area. Ada is a great lang= uage for implementing in memory databases. At MITRE I worked on both groun= d based and in-flight radar systems. The emphasis was on consistency and n= on-blocking.=20 After a system crash or power failure, rather than reconstruct the previous= state, the usual goal was to restart as fast as possible, so some or all o= f the previous data was ignored. Restoring (name) tags to tracks was very = much a nice to have, but couldn't be done until you had several detections = to combine into a track, which took many seconds. (Both airborne and groun= d radars often stop emitting for short periods for various reasons includin= g incoming missiles. In those restarts you may or may not be able to match= tracks with the old data. Big Waah! Extra work for operators is a small p= rice to pay for survival.) =20 Anyway it was much, much easier to "roll your own" Ada database than use a = commercial database. Why? Commercial databases are not real-time systems.= In a radar system you may need transactions to complete in N milliseconds= for a relatively small N, while commercial databases consider 2 seconds av= erage response times good enough. With this particular Ada "trick" each tr= ack record could have its own lock, and threads could cache the address of = the record and lock it only when necessary. Transaction times were on aver= age microseconds, with 2 or 3 milliseconds being worst case.