bobD

Sounds like a reasonable hypothesis, because this has been my main development machine for a few years now, and has seen multiple IB versions. Also the results are the same whether I try the sample app, or connecting to a local copy of my actual intended target db. I'll try to see what I can find this week after looking at cleaning up the installation. Thanks, bobD

Thanks for response. I also looked at and followed along with the set-up demo at but no joy. At the end the project could not connect. Still trying to figure out what's wrong with the installation. May try uninstalling and reinstalling PAServer next. I have similar outcome with the FireIBLite.dproj sample. If the local IBServer is running, I get a user name and password not defined error, If I check the Lite option and stop the local server, then I get database unavailable. Very frustrating... bobD

Absolutely. The inclusion of Free in the instance method is essentially a side-effect of the method and constitutes a violation of the SRP. What if I want to call DoSomething twice? Also, as a matter of consistency I personally always call the inherited constructor--even when descending from TObject directly. I have no guarantee that TObject.Create will always be an empty method.

Currently running IB 2020 server, using Delphi 11 Arch, via FireDac Everything fine with that, but want to add offline capability. Is there a simple embedded-IB sample project available anywhere. I need to know what dlls to use and include with application. Intent is to have the application request a connection, then the connection unit --return a server connection if on the local network, or --if not return the local imbedded connection Alternative might be to always open local, then handle network synch if on the network Database is low volatility (read often, write seldom) thanks, bobD

"I need to know if any lists are the same as my list." This implies an 'active record' where the question is really "does list <x> (my list) already exist in set of lists <y>" "if any two rooms have exactly the same booking schedules." This implies a much more complex question: "given set of lists <y>, are any two [or more] lists the same?" (basically, an iteration of the first question where x = 0 to number of lists -1.) which is it? Suppose a user changes a date-item for a room. One of four things happen: --the list, previously distinct, is now a duplicate of another --the list, previously a duplicate of another, is now distinct --the list was and remains distinct --the list was and remains a duplicate Can we rule out any of these cases as impossible? Does anything have to happen as a result of any of these cases? (For example, the change not being allowed) Is there any persistence aspect to the question? What's being stored? My initial design thought is to maintain a sorted list of list hashes, so that the question "does list <x> (my list) already exist in set of lists <y>" is a simple look-up on the list hash (which can itself be calculated and stored with the list whenever it changes). however, the statement "The dates change frequently, the comparison gets run infrequently" makes the whole idea of pre-calculation a case of swimming upstream. You don't generally make a frequent operation slower in order to speed up a relatively infrequent operation. So I agree with Joseph Mitzen's response that cautioned that some instrumentation is called for.

four questions: 1. Where do the datetimes come from and how/when do they change? For example, if you're comparing file datetimes, then maintaining a status when the data changes might be better than checking when you need to know. They might change a lot less often than you check for a difference. 2. What is it you really need to know: whether any particular pair is different? or whether any difference exists anywhere in the list? 3. Is that always simply a 'difference exists' boolean? Or would knowing [greater than | equal to | less than] also needed? 4. Is there a guarantee that for every element[x] in list one, the same element exists at position[x] in list two? How is that guarantee enforced or checked? All of these affect your potential solution options. For the first example, if the list changes much less often than the need to check, then you might create a tracking object with two boolean values: FUpdated and FDifferent. Set FUpdated to true when any list element changes. When checking, if FUpdated is false, then simply return the FDifferent boolean, or if true recheck the list, store and return the comparison operation result, and reset FUpdated to false. This can save you thousands of list comparisons if the lists are much less volatile than the need to know whether they're the same. Answers to the other questions could modify the structure of this tracking object.

My sincere condolences to his family and all who knew him. Many of us continue to live by choice largely in the mental universe he architected. bobD

That encourages me that I'm on the right track with bitmaps. I'll report back with some further testing.

In what regard? What I know so far is this: the lines img.Scale := jsEighth; img.Performance := jpBestSpeed; speed up the load/display of the jpg file as advertised Using the following code, bmp := TBitMap.Create(img.Width, img.Height); bmp.Assign(img); bmp.SaveToFile('C:\Users\bobd\Desktop\TestBMP.bmp'); and starting with a jpg file of 15.4 MB results in a bmp file of about 1.14 MB if Scale and Performance are so specified, or with the lines commented out 73MB (!). That suggests to me that there's no direct calculation of the JPGImage size from the bitmap it produces. You can see either a > 10x reduction, or a 4-5x expansion. Interestingly though, the TJPGImage object saving itself to file after the scale and performance are reduced for load results in a file the same size as the original. So we can't assume that the TJPGImage so loaded is any smaller in memory that one loaded without the jsEighth reduction. That's interesting. It appears to me that the most memory efficient cache (and thus the one with the largest practical capacity) for this app is going to be loading at jsEighth, then creating and caching the bitmap. Since the original image can be 6192 x 4192, I don't really need all that resolution anyway. Unfortunately, this presumes something not in evidence: that the size of the TBitmap in memory has a direct relationship to its file size. As with the source TJPGImage, it doesn't have an accessible size-in-memory property.

I can do that. Is that suggested for performance or memory footprint? It bugs me that I can't see what I'm doing. InstanceSize returns 100 bytes for the img, 24 bytes for the stream. Obviously neither really accounts for the data. bobD

I'm working on a quick photo browsing app, using a TObjectDictionary<string, TJPEGImage> as a cache device. Images are requested for display using the path to the jpg file like this: procedure TJpgStore.LoadPicture(aPicture: TPicture; const aSource: string); var img : TJPEGImage; begin if not FDict.TryGetValue(aSource, img) then begin img := TJPEGImage.Create; img.Scale := jsEighth; img.Performance := jpBestSpeed; img.LoadFromFile(aSource); FDict.Add(aSource, img); end; aPicture.Assign(img); end; This all seems to work fine, but two questions (since I'm not really a graphics guy): Am using Scale and Performance correctly? IOW, does it make any difference being here or after the LoadFromFile call? How much memory does a loaded TJPGImage take up? ('m thinking about a least-recently-used cache size governor. The jpgs are commonly 15-25MB each, and a source directory might contain 1-5,000 picture, so caching them all doesn't seem realistic...) Those are specific questions, but glad to entertain other comments/suggestions/alternative approaches. Thanks, bobD

For whatever reason I've never used cached updates. Fuller context is that I have an app on my local home network that uses an IB server. There are two main failure conditions: (1) the laptop's Wifi connection to the server is wonky, or (2) I'm off traveling and not on the home network at all. I'm currently considering three different architectural approaches as I go from simple C/S design to briefcase (or more generally a 'network-optional' design). 1. Use IB's built-in change views--this would be preferred if I could find a decent tutorial for getting started. Major documentation shortfall here. 2. Use a server first approach (app tries to connect to IB server, failing that it opens local IB database). Obviously that requires I write a server<-->local reconciliation routine. 3. Use a local-first approach. That removes the need for solving the network slow-fail issue, because all server communication would be confined to the background reconciliation thread.

Thanks for suggestion. I've actually isolated the problem at this point to the WiFi connection being flaky, since the app works fine on the wired-in network machines even as the laptop fails to connect, and stopping/starting the laptop wifi service always fixes the problem. The DB machine and DB are solid as a rock. One of the things I'm thinking about doing as the app evolves is making it briefcase-enabled by running an local DB, and having the app run locally if the server isn't available. That creates an obvious synchronization requirement of course, and hence my interest in learning about change views. But that might be way more complicated than I actually need--the data at this point is pretty stable.

I'll probably go with that for the moment. And I'll admit that 'seeming forever' is a very subjective complaint. The app normally opens with a fully populated dataset w/i a second or 2, so waiting is just waiting for inevitable exception handler. bobD

Thanks Fr0st-- See my reply to Anders--Given the type of connection fails I get, I'm not actually looking for a 100% solution. Unreliable might be fine depending on why the test fails. For example, I wonder whether I can ask the router if the sever is available rather than even trying to even talk to it. The server itself doesn't publish for network browsing, nor does it even respond to pings--effectively it's stealth except for the database connection (on the standard 3050 port).