I am currently developing a Rhomobile application. I have a backend database which holds customer information. I have got from the webserver a csv string (or XML - I am able to parse the XML using REXML) which contains all the customers. Each time I sync the device I am going to reset the customer table on the device and re-insert all data from the backend database. I am not using RhoSync and the device will be using property bag.
Is it possible to use the CSV or XML data to insert into the customers table? If so, how would I go about it?
At the moment the only option I can see that would work would be to manually loop through the CSV/XML and insert into the database manually; this isn't very elegant.
Any help will be much appreciated, sorry if this is a dumb question; still relatively new to this framework.
I have come to the conclusion that the only way is to loop through the csv/xml, which with the help of a database transaction this doesn't take long.
Using fixed schema also increases the performance a lot as property bag has to do column inserts (so if you have lots of columns - there is lots of inserts per record).
Also in Rhomobile garbage collection is turned off, so if you are trying to process large data sets your device will quickly run out of memory:
GC.enable
The above solves this issue
Related
We have 10 servers.Some flight related data will come to the servers.From servers that data will come to our application.Means same data can come to our application more than one time,but finally i need to save that data only once in the database.So we are checking in the database before inserting the data.If that record is already not exist in the database then only we are going to save the data.But for some reason we are getting duplicate records in the database.
Is it necessary using synchronization in this scenario.
What might be the problem here.Thanks in advance...
In our company the way we deal with multiple data sources where same piece of information may go through is by utilizing batches.
What we found is by doing this at code level (java and .NET), we would invest a lot of devops time and still have duplications.
By implementing a batching process we stored everything locally and process using 2 batch jobs.
1st will ensure quality of data and remove duplications
2nd will compress and push data to our persistence service (we use XCOM to push straight into a db queue which then plugs the data in).
If you can implement something similar because you have a central point of entry upon which you can implement proper quality gates.
Hope our example helps, if not let me know happy to remove this. :)
I have a Ruby application Postrgress DB on heroku.
Some of the data is was migrated incorrectly.
I want to update the data on about 5 thousand rows. I do not want to blow the DB away and remigrate.
What would be the best way to do this.
I have update small amounts of data using the active record type sql but not sure for a large amount.
thanks in advance
Maggs
It really depends on how many fields or what type of data you specifically you are trying to change.
Are your fields changing specifically for each one or are you able to run a loop to iterate through each row to update the value? Please be more specific in terms of the data and what kind of editing you are trying to do.
I am working on a WP7 app that contains
CategoryGroups
Categories
Products
The rows for each of these entities are populated on first run of the application.
The issues is that when the app gets published, the rows in each of the entities will change (added, deleted, modified). I would like some suggestions on how I should handle this? Any pointers to existing code samples will be great?
I am using an object oriented database to store my entities. The app also allows the user to add their own entities (which get added to the database as personalized (flagged) entities). One solution I was thinking was to read an xml file from the server and then loop through the database entries and make the necessary modifications in the database. So, on the first run, all the entities will just get inserted. On subsequent runs, if the version number attribute in xml is different, then the system populated data is reloaded from xml but the user data is preserved.
Also, maybe only check for the new xml file on the server when internet connection is available and only periodically (like every 2 weeks).
Any other suggestions are welcome. If there is a simpler, cleaner way - please share.
Pratik
I think it's fair to say that this question has nothing to do with WP7 and everything to do with finding an efficient way to to compute and deliver update deltas.
Timestamp your items. When requesting an update, specify the time of last update. You server can trivially query for items newer than this and return a delta. At the client (ie in the phone) it is not necessary to store a last update time because you can simply add one second to the most recent timestamp in the items present on the phone.
I have a web application in Spring that has a functional requirement for generating a CSV/Excel spreadsheet from a result set coming from a large Oracle database. The expected rows are in the 300,000 - 1,000,000 range. Time to process is not as large of an issue as keeping the application stable -- and right now, very large result sets cause it to run out of memory and crash.
In a normal situation like this, I would use pagination and have the UI display a limited number of results at a time. However, in this case I need to be able to produce the entire set in a single file, no matter how big it might be, for offline use.
I have isolated the issue to the ParameterizedRowMapper being used to convert the result set into objects, which is where I'm stuck.
What techniques might I be able to use to get this operation under control? Is pagination still an option?
A simple answer:
Use a JDBC recordset (or something similar, with an appropriate array/fetch size) and write the data back a LOB, either temporary or back into the database.
Another choice:
Use PL/SQL in the database to write a file using UTL_FILE for your recordset in CSV format. As the file will be on the database server, not on the client, Use UTL_SMTP or JavaMail using Java Stored Procedures to mail the file. After all, I'd be surprised if someone was going to watch the hourglass turn over repeatedly waiting for a 1 million row recordset to be generated.
Instead of loading an entire file in memory you can process each row individually and use output stream to send the output directly to the web browser. E.g. in servlets API, you can get the output stream from ServletResponse.getOutputStream() and then simply write result CSV lines to that stream.
I would push back on those requirements- they sound pretty artificial.
What happens if your application fails, or the power goes out before the user looks at that data?
From your comment above, sounds like you know the answer- you need filesystem or oracle access, in order to do your job.
You are being asked to generate some data- something that is not repeatable by sql?
If it were repeatable, you would just send pages of data back to the user at a time.
Since this report, I'm guessing, has something to do with the current state of your data, you need to store that result somewhere, if you can't stream it out to the user. I'd write a stored procedure in oracle- it's much faster not to send data back and forth across the network. If you have special tools or its just easier, sounds like there's nothing wrong with doing it on the java side instead.
Can you schedule this report to run once a week?
Have you considered the performance of an Excel spreadsheet with 1,000,000 rows?
I have a table of non trivial size on a DB2 database that is updated X times a day per user input in another application. This table is also read by my web-app to display some info to another set of users. I have a large number of users on my web app and they need to do lots of fuzzy string lookups with data that is up-to-the-minute accurate. So, I need a server side cache to do my fuzzy logic on and to keep the DB from getting hammered.
So, what's the best option? I would hate to pull the entire table every minute when the data changes so rarely. I could setup a trigger to update a timestamp of a smaller table and poll that to see if I need refresh my cache, but that seems hacky to.
Ideally I would like to have DB2 tell my web-app when something changes, or at least provide a very lightweight mechanism to detect data level changes.
I think if your web application is running in WebSphere, setting up MQ would be a pretty good solution.
You could write triggers that use the MQ Series routines to add things to a queue, and your web app could subscribe to the queue and listen for updates.
If your web app is not in WebSphere then you could still look at this option but it might be more difficult.
A simple solution could be to have a timestamp (somewhere) for the latest change on to table.
The timestamp could be located in a small table/view that is updated by either the application that updates the big table or by an update-trigger on the big table.
The update-triggers only task would be to update the "help"-timestamp with currenttimestamp.
Then the webapp only checks this timestamp.
If the timestamp is newer then what the webapp has then the data is reread from the big table.
A "low-tech"-solution thats fairly non intrusive to the exsisting system.
Hope this solution fits your setup.
Regards
Sigersted
Having the database push a message to your webapp is certainly doable via a variety of mechanisms (like mqseries, etc). Similar and easier is to write a java stored procedure that gets kicked off by the trigger and hands the data to your cache-maintenance interface. But both of these solutions involve a lot of versioning dependencies, etc that could be a real PITA.
Another option might be to reconsider the entire approach. Is it possible that instead of maintaining a cache on your app's side you could perform your text searching on the original table?
But my suggestion is to do as you (and the other poster) mention - and just update a timestamp in a single-row table purposed to do this, then have your web-app poll that table. Similarly you could just push the changed rows to this small table - and have your cache-maintenance program pull from this table. Either of these is very simple to implement - and should be very reliable.