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I'm looking for a key/value store meeting the following requirements:
Open Source
C API (C++ okay too)
ACID
Some level of crash recovery
High [storage] capacity per file
Both key and value are arbitrary binary data
Embedded (like DBM, SQLite, et al.)
GDBM looks particularly attractive. Per the fact that the datum struct uses int dsize; clearly key and value sizes are limited to 2GB, which is fine. However, my problem with GDBM is that I can't find any documentation on the limit to the database file sizes. For example, Berkeley DB provides database files up to 256TB. If this is large enough, then GDBM would be perfect.
Does anyone know the GDBM file size cap? Failing that (or if it's too small) what other suggestions can you make? Does such a beast exist?
If you're using GDBM on a 32-bit (i386) system, the maximum database size is 2GB. If you're using it on a 64-bit system and you compile your app 64-bit, then the maximum database size should be limited by your filesystem.
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I have a program with a priority queue (PQ) so huge that it does not fit to the memory. It was decided to move some data to MySQL database (DB) in following way: the new elements are put into DB instead of PQ, and when the PQ is emptied, it is updated by the entries in the DB. But this way appeared to spoil the priority ordering. Is there any solution which does not corrupt the priority ordering and combines PQ with DB?
For some reason I cannot get rid of PQ and use only DB.
Your question is rather vague on the functionality, but I think the idea is wrong.
Someone seems to have the idea of using the database as secondary storage for an in-memory application. That doesn't really make much sense. Normally, you would use a simple file for this. Although you can use a database for managing secondary/tertiary storage, a database does many other things, so it is like using a smart phone only as a clock.
If you are going to use a database, then store the entire structure in the database and develop an API for it that meets your needs.
If you want help with how to structure the data, then write another question and include:
sample data
how the priority queue will be used
any ideas you have on the data structure
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I'm using mysql for my database needs and the total size is ~1.5 TB.
I'm looking for a Business intelligence tool which gives me an interface to fetch reports in any desired format to help decision making. The user shall be able to sum, sort, count, sum in various ways.
I don't know what shall I do about it.
In the past few days, I've read dozen of articles and watched many videos about Bigdata, hadoop, BIRT, Solr, Cassandra, mongodb, noSql and just everything that popped in search suggestions for my queries on BI but can't decide what's the right tool for me.
Is there a tool available to help me with my Data reporting and visualizing needs?
Did you read about Tableau (http://www.tableausoftware.com/)? Its a very nice data visualization tool (though not free but worth it) and can connect to various data sources (mysql, hive etc). Also it provides options to do all such operations you mentioned. It will be worth to evaluate it once.
It provides a 15 day free version. You can try out and see if it fits your needs.
Try Google Big Query, it should solve your issue
https://cloud.google.com/bigquery/
For syntax, please refer
https://cloud.google.com/bigquery/query-reference
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Did the first operating system programmed in binary?
I'm just curious because It looks like that it should be programmed in binary. But if it's really binary , how would that first programmers know what to write the programs? Isn't he in total blindness?
Also , can you give me the example of command in binary?(First operating system's function if possible).
The very first computers (like e.g. Eniac) did not have any operating system. People programmed them in e.g. binary! Then some guy decided to develop a monitor (which later was called, and evolved in, an operating system).
Even in the 1960s some computers (like the IBM 1620) where able to start without any code (at that time they had no firmware and no ROM): I am old enough to have played, as a teenager, on one (in a museum): you was able, by setting special switches, to type the few machine instructions (in BCD) to load the rest of the system (on punched tapes).
It is a classic bootstrapping problem. J.Pitrat's blog on bootstrapping artificial intelligence should have useful references.
Read about history of computing software & history of operating systems.
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I want to learn how to play with RFID... Read it, write it, scan for it.
I need the software to do this as well as the hardware.
I'm not 100% sure what my end goal is. So, the more sources is get, the better. Keep the comments coming.
The actual hardware to read tags is not so complicated. You can get a reader like this one that can read tags fairly simply. The scanner just sends a unique 10 byte code every time it reads a tag, and you can handle that in just about any software fairly trivially.
I have never written tags because I have never found a need to. You can get tags for under a dollar each, and they all have a unique key. I just record them into my system and store them.
I use rfid for a basic entry control system on my front door, using an arduino controller to send the codes to my central server, and then to open an electronic lock. My setup is sort of similar to what is described here. My server allows me to remotely access it, and to set up specific time based access restrictions for individual tags. The microcontroller is not strictly required, but it allows me an easy way to interface with various hardware elements.
I think you have these options to use for your requirement:
Tikitag RFID Programming Kit http://www.jeremyperson.com/tikitag-rfid-programming-kit/ or this RFID Programming Kit http://www.phidgets.com/products.php?category=14
I hope that helps!
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My software needs to read a fixed-length handwritten number.
While I could use a general-purpose library like Tesseract, I am sure there is something smarter. Tesseract will probably misinterpret some of the 1 or 7 as I or l, whereas a software that expects only numbers would not.
Knowing that there are only numbers (American-English way of writing them), the algorithm could focus on 10 potential matches instead of hundreds of symbols.
Any experience OCRing handwritten number-only fields?
What open source library/software did you get the best results with?
From the FAQ of Tesseract:
How do I recognize only digits?
In 2.03 and above:
Use
TessBaseAPI::SetVariable("tessedit_char_whitelist", "0123456789");
before calling an Init function or put this in a text file called tessdata/configs/digits:
tessedit_char_whitelist 0123456789
and then your command line becomes:
tesseract image.tif outputbase nobatch digits
Warning: Until the old and new config variables get merged, you must have the nobatch parameter too.
But I think since it was designed for printed—not handwritten—text, accuracy might suffer even for digits only.