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Steven, >Date: Thu, 16 Sep 2004 20:53:48 -0500 >From: "Steven Danz" <address@hidden> >Organization: Aviation Weather Center >To: Steve Emmerson <address@hidden> >Subject: Re: 20040913: Possible pqact issue in LDM? > Keywords: 200409142045.i8EKjBnJ016694 LDM-6 ldmadmin pqact.conf The above message contained the following: > So far so good, but I'm wanting to give it some time. :-) Same here. About how often, however, has your pqact(1) missed data-products? > I've been mulling it around and had a few questions. > > 1) Noticed the changes in pqact and was wondering if the rpc.ldmd uses > the same or a similar method to determine which products go to > downstream clients. The changes to the pqact(1) program should not be relevant to the problem you're seeing: they addressed other issues. > If so, could it be possible that this might > cause a server to not pass products down to a client? I've had a > problem once in a blue moon where a product upstream doesn't show > up down, but I've always seemed to convince myself it was 'something > else'. Both pqact(1) and sending rpc.ldmd(1) processes use the pq_sequence(3) function of the pq(3) module. This function is responsible for sequencing through all desired data-products in the product-queue. I hope that changes to this module will stop pqact(1) from skipping data-products. This should also eliminate any similar behavior by sending rpc.ldmd(1) processes. > 2) The timestamp that is assigned when the product is placed in the > queue, is it preserved as the product passes from server to client? No. What goes along with the data-product as part of its metadata is the creation-time of the data-product. The insertion-time of a data-product into a product-queue is local to the system only and is not communicated between LDM-s. > If so, if there were 4 data sources feeding one client, then > there exists a chance (regardless of the speed of the systems) > that a duplicate timestamp could be created by the data sources. It does, indeed, seem possible that, on a fast system, more than one data-product could have the same insertion-time -- especiall during a reconnection when the downstream LDM is "catching up". > 3) Even if the timestamp is reassigned by the client, if the client > had multiple upstream sources, and therefore multiple rpc.ldmd > processes inserting products in the queue, it would seem (especially > on multiple CPU systems) that the multiple client rpc.ldmd processes > would stand a pretty good chance of creating duplicate timestamps. Warren Blanchard at the national NWS HQ has reported missing about 8 NEXRAD Level II data-products per 100,000 data-products (a 0.008% loss rate). This seems similar to your pqact(1) problem. > True, for a single-CPU system it would take a pretty fast system > (and pretty small products), but I would think that with an n-way > system it would more likely. I agree. Hopefully, the new pq(3) module will fix this. > Like I said, just some random thoughts. Thanks for the work on this! > > Steven > > Steven Danz > Senior Software Development Engineer > Aviation Weather Center (NOAA/NWS/NCEP) > 7220 NW 101st Terrace, Room 101 > Kansas City, MO 64153-2371 > > Email: address@hidden > Phone: 816.584.7251 > Fax: 816.880.0650 > URL: http://aviationweather.gov/ > > The opinions expressed in this message do not necessarily reflect those > of the National Weather Service, or the Aviation Weather Center. Regards, Steve Emmerson