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  • How to overcome an apparent REST vs. DRY dilemma in rails?

    - by Chris
    A rails app I'm working on features examples of quadratic equations. Obviously, these are all of a common structure: ax^2 + bx + c = 0. I don't want to store every single example of these. I'd rather generate them from a template. Storing hundreds of possible versions of this structure seems highly wasteful and un-DRY. On the other hand, if I generate them, I can't access them again reliably as I could if they were simply multiple database objects. I'm sure there must be a way to overcome this, but I'm still learning rails and I'm obviously not grasping something here. Thanks.

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  • free public databases with non-trivial table structures?

    - by Caffeine Coma
    I'm looking for some sample database data that I can use for testing and demonstrating a DB tool I am working on. I need a DB that has (preferably) many tables, and many foreign key relationships between the tables. Ideally the data would be in SQL dump format, or at least in something that maintains the foreign key references, and could be easily import into an RDBMS (MySQL or H2). The dataset itself doesn't have to be huge (in fact, best if it's not). I thought about using the Stackoverflow Data Dump, but it's only about 5 tables.

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  • How active record is automatically setting up the autoincremental value of ID?

    - by piemesons
    Here this is what we are doing:-- an_order = Order.new an_order.name = "Dave Thomas" an_order.email = "[email protected]" an_order.address = "123 Main St" an_order.pay_type = "check" an_order.save Now it will insert a new row in orders table right. I m having a ID column in that table. Now suppose after inserting this record the value of the ID corresponding to this record is 100. Now how this 100 value came to know? Does the previous value of ID ie 99 (Suppose) is stored somewhere in some variable/file in the ORM layer or before inserting this value a query was fired to know about the last inserted value or database is itself doing that or anything else???

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  • checking if records exists in DB, in single step or 2 steps?

    - by Sinan
    Suppose you want to get a record from database which returns a large data and requires multiple joins. So my question would be is it better to use a single query to check if data exists and get the result if it exists. Or do a more simple query to check if data exists then id record exists, query once again to get the result knowing that it exists. Example: 3 tables a, b and ab(junction table) select * from from a, b, ab where condition and condition and condition and condition etc... or select id from a, b ab where condition then if exists do the query above. So I don't know if there is any reason to do the second. Any ideas how this affects DB performance or does it matter at all?

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  • Active Record/ORM vs Normal Forms?

    - by Arsenal
    Hello, I've been playing around with Active Record a bit, and I have noticed that A.C./ORM always uses the following database model when creating a one-to-one relationship Person id | country_id | name | ... Country id | tld | name | ... No I wondered, isn't this a violiation of the third Normal Form? This clearly states "Every non-prime attribute is non-transitively dependent on every key of the table". Well this country_id isn't dependent of personid is it? So is this wrong or am I just not getting the point?

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  • In django models, how to make all table names not have the app label?

    - by Luigi
    I have a database that was already being used by other applications before i began writing a web interface with django for it. The table names follow simple naming standards, so the django model Customer should map to the table "customer" in the db. At the same time I'm adding new tables/models. Since I find it cumbersome to use app_customer every time i have to write a query (django's ORM is definitely not enough for them) in the other applications and I don't want to rename the existing tables, what is the best way to make all models in my django app use tables without applabel_, besides adding a Meta class with db_table= to each model? Is there any reason why I shouldn't do this? I have only one web app that needs to access this db, everything else doesn't use django models.

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  • Application Buddy Lists and Authentication - How does it all go together

    - by Krevin
    This is a broad but specific question. The idea is that we want to tie in a 'buddy' functionality to a communications app. Very broadly, I believe that the application clients would connect to a central database/auth service which would provide the buddy data and then allow client apps to connect directly to eachother, without passing communications through the server. Specifically, however, what solutions, software, products, servers, technologies, etc would be best to implement to handle such a task? Thanks for reading and responses are much appreciated. //edit: the com app may run on a linux distro, may be web based, or both

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  • Resources to learn about engineering aspects of data analytics (OLAP, warehousing, ETL, etc.)

    - by JT
    I'm a math/stats guy, interested in learning more about the engineering aspects of "data analytics" (this may be an overly broad term, this is a case of "I don't know what I don't know", so I'm not sure how to be more specific). I'm fine with manipulating and analyzing the data once it's already stored somewhere and I can access it, and I'm fine with writing scripts and SQL queries (and have a general knowledge of things like normalization). What I don't know is the whole engineering process of capturing and storing the data. For example, terms I've heard thrown about that I only vaguely understand the meaning of include: - OLAP, OLTP - Data warehousing - ETL - ??? What's a good book (or any other resource) to learn about these kinds of things? What are things I should know about database design (normalization seems kinda "obvious" to me, something I would have done even before I knew the term -- is there anything else?)? In other words, for jobs falling under the umbrella term of "analytics engineer", what kinds of things should I know?

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  • Using Entity Framework for SQL Compact Edition 3.5 does not respect mode=exclusive property of conne

    - by AJ
    I am using SQL Server Compact 3.5 edition with Entity Framework and I want to have exclusive lock on the database as documented here http://msdn.microsoft.com/en-us/library/ms171817.aspx. However when you pass this in a connection string to Entity Framework it does not respect this at all. An example of the connection string as following private static readonly string _ConnectionStringFormat = @"metadata=res://*/Model.csdl|res://*/Model.ssdl|res://*/Model.msl; provider=System.Data.SqlServerCe.3.5; provider connection string='Data Source={0};Mode=Exclusive'"; If anyone has come across this issue before and have found out how to resolve this, then please let me know. Thanks Aj

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  • Graph Databases' Implementation

    - by user1478153
    I am having trouble visualizing a Graph Database. Visualizing an RDBMS is really very simple and I was able to understand from the first tutorial itself when I started learning it some 4-5 years ago. But I am not able to understand Graph Databases. I am also unable to get any good links on this topic, hence posting this question here. Specifically, I am looking for the following: Some really simple book/link on Graph Dbs Atleast some knowledge on the implementation details of a Graph DB (I hope all Graph DBs would be having atleast a few basic things in common). Thanks a lot in advance guys,

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  • Classic ASP Site Throwing Date Conversion Error After Moving Servers?

    - by leen3o
    I am moving an old store from a Win2003 IIS6 server to a Win2008 IIS7 server, moved everything across including database. The front end seems to work just fine, but when I login it has to do pull in data based on date ranges and now from no where I am getting this error? The conversion of a varchar data type to a datetime data type resulted in an out-of-range value Any ideas why this would do this on the new server and NOT on the old one? No code has changed and the DB is a backup of the one from the old server??

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  • Statically Compiled Oracle Client Drivers/Code

    - by blockcipher
    Hello, I'm looking to write a command-line program that can execute database scripts against an Oracle server, however the machine the program will be run on may not have an Oracle client installed on it. I also don't want to rely on a language that requires a VM as there's no guarantee that the VM will be installed, so a language like C is preferable for this. Is there a way that I can statically compile/build this program and not have to have the user install the Oracle client on that machine? I'm trying to be as unobtrusive as possible. Thanks.

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  • Dynamic table design (common lookup table), need a nice query to get the values

    - by Swoosh
    sql2005 This is my simplified example: (in reality there are 40+ tables in here, I only showed 2) I got a table called tb_modules, with 3 columns (id, description, tablename as varchar): 1, UserType, tb_usertype 2, Religion, tb_religion (Last column is actually the name of a different table) I got an other table that looks like this: tb_value (columns:id, tb_modules_ID, usertype_OR_religion_ID) values: 1111, 1, 45 1112, 1, 55 1113, 2, 123 1114, 2, 234 so, I mean 45, 55, 123, 234 are usertype OR religion ID's (45, 55 usertype, 123, 234 religion ID`s) Don't judge, I didn't design the database Question How can I make a select, showing * from tb_value, plus one column That one column would be TITLE from the tb_usertype or RELIGIONNAME from the tb_religion table I would like to make a general thing. Was thinking initially about maybe a SQL function that returns a string, but I think I would need dynamic SQL, which is not ok in a function. Anyone a better idea ?

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  • Need alternative field names for these reserved words

    - by MattSlay
    “type” and “class” are likely reserved or problematic words in C# and/or Ruby, two languages I may use to program against my new database schema in the future. So, in order to avoid potential conflicts with those languages, I’m looking for alternative names for these field names in my tables. In this case, it is from my Machines table, where I have: “class” field (values would be something like “manual” or “computerized”) and “type” field (values would be “lathe” or “mill”) I could call the fields “machineclass” and “machinetype”, but that is inconsistent with naming scheme in the rest of my schema (meaning, I do not re-use the table name in the field… For instance, I use Machine.name, not Machine.machinename) Any thought on this madness?

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  • How do I find the top N batters per year?

    - by Drew Stephens
    I'm playing around with the Lahman Baseball Database in a MySQL instance. I want to find the players who topped home runs (HR) for each year. The Batting table has the following (relevant parts) of its schema: +-----------+----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+----------------------+------+-----+---------+-------+ | playerID | varchar(9) | NO | PRI | | | | yearID | smallint(4) unsigned | NO | PRI | 0 | | | HR | smallint(3) unsigned | YES | | NULL | | +-----------+----------------------+------+-----+---------+-------+ For each year, every player has an entry (between hundreds and 12k per year, going back to 1871). Getting the top N hitters for a single year is easy: SELECT playerID,yearID,HR FROM Batting WHERE yearID=2009 ORDER BY HR DESC LIMIT 3; +-----------+--------+------+ | playerID | yearID | HR | +-----------+--------+------+ | pujolal01 | 2009 | 47 | | fieldpr01 | 2009 | 46 | | howarry01 | 2009 | 45 | +-----------+--------+------+ But I'm interested in finding the top 3 from every year. I've found solutions like this, describing how to select the top from a category and I've tried to apply it to my problem, only to end up with a query that never returns: SELECT b.yearID, b.playerID, b.HR FROM Batting AS b LEFT JOIN Batting b2 ON (b.yearID=b2.yearID AND b.HR <= b2.HR) GROUP BY b.yearID HAVING COUNT(*) <= 3; Where have I gone wrong?

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  • Drupal: I cannot connect to the database.. please help

    - by Patrick
    hi, I've hard time to make Drupal work on IIS Microsoft server. I've succesfully run Joomla on the same server so I'm pretty sure the following information are correct: host: localhost user: user pass: pass databaseName = servername_databasename I've set the following line in settings.php file: $db_url = 'mysql://user:password@localhost/servername_databasename'; but what I get is this: If you are the maintainer of this site, please check your database settings in the settings.php file and ensure that your hosting provider's database server is running. For more help, see the handbook, or contact your hosting provider. I don't get any other error message such as: database doesn't exist, user/pass wrong.. just this. The database is running, I can access with phpmyadmin. I've tried both "mysql" and "mysqli". The host is a private server (IIS Microsoft), the database is Mysql The database and website files upload have also been succesfull.. so I dunno what to do to fix this issue. thanks

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  • "Data type mismatch in criteria expression"

    - by simon
    Hey guys ! I have a problem when i want to insert values from textboxes to my access database ! When i want to save i get that error ("Data type mismatch in criteria expression") The code: string conString = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=C:\Users\Simon\Desktop\test5\test5\test5\save.mdb"; OleDbConnection empConnection = new OleDbConnection(conString); string insertStatement = "INSERT INTO aktivnosti_save " + "([ID_uporabnika],[ID_aktivnosti],[kalorij]) " + "VALUES (@ID_uporabnika,@ID_aktivnosti,@kalorij)"; OleDbCommand insertCommand = new OleDbCommand(insertStatement, empConnection); insertCommand.Parameters.Add("@ID_uporabnika", OleDbType.Char).Value = textBox3.Text; insertCommand.Parameters.Add("@ID_zivila", OleDbType.Char).Value = iDTextBox.Text; insertCommand.Parameters.Add("@kalorij", OleDbType.Char).Value = textBox2.Text; empConnection.Open(); try { int count = insertCommand.ExecuteNonQuery(); } catch (OleDbException ex) { MessageBox.Show(ex.Message); } finally { empConnection.Close(); textBox1.Clear(); textBox2.Clear(); } }

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  • Refresh databases data

    - by Simon
    How can i refresh the data from my database(ms access) in c# using windows form aplication? part of the code where i insert the data : insertCommand.Parameters.Add("@ID_uporabnika", OleDbType.Integer).Value = Convert.ToInt32(textBox6.Text); insertCommand.Parameters.Add("@datum", OleDbType.DBDate).Value = DateTime.Now.ToShortDateString(); insertCommand.Parameters.Add("@ID_zivila", OleDbType.Integer).Value = Convert.ToInt32(iDTextBox.Text); insertCommand.Parameters.Add("@skupaj_kalorij", OleDbType.Double).Value = Convert.ToDouble(textBox1.Text); empConnection.Open(); try { int count = insertCommand.ExecuteNonQuery(); } catch (OleDbException ex) { MessageBox.Show(ex.Message); } finally { empConnection.Close(); MessageBox.Show("zauižiti obrok je bil shranjen"); textBox1.Clear(); textBox2.Clear(); textBox3.Clear(); textBox4.Clear(); textBox5.Clear(); } }

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  • Router 2wire, Slackware desktop in DMZ mode, iptables policy aginst ping, but still pingable

    - by skriatok
    I'm in DMZ mode, so I'm firewalling myself, stealthy all ok, but I get faulty test results from Shields Up that there are pings. Yesterday I couldn't make a connection to game servers work, because ping block was enabled (on the router). I disabled it, but this persists even due to my firewall. What is the connection between me and my router in DMZ mode (for my machine, there is bunch of others too behind router firewall)? When it allows router affecting if I'm pingable or not and if router has setting not blocking ping, rules in my iptables for this scenario do not work. Please ignore commented rules, I do uncomment them as I want. These two should do the job right? iptables -A INPUT -p icmp --icmp-type echo-request -j DROP echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all Here are my iptables: #!/bin/sh # Begin /bin/firewall-start # Insert connection-tracking modules (not needed if built into the kernel). #modprobe ip_tables #modprobe iptable_filter #modprobe ip_conntrack #modprobe ip_conntrack_ftp #modprobe ipt_state #modprobe ipt_LOG # allow local-only connections iptables -A INPUT -i lo -j ACCEPT # free output on any interface to any ip for any service # (equal to -P ACCEPT) iptables -A OUTPUT -j ACCEPT # permit answers on already established connections # and permit new connections related to established ones (eg active-ftp) iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT #Gamespy&NWN #iptables -A INPUT -p tcp -m tcp -m multiport --ports 5120:5129 -j ACCEPT #iptables -A INPUT -p tcp -m tcp --dport 6667 --tcp-flags SYN,RST,ACK SYN -j ACCEPT #iptables -A INPUT -p tcp -m tcp --dport 28910 --tcp-flags SYN,RST,ACK SYN -j ACCEPT #iptables -A INPUT -p tcp -m tcp --dport 29900 --tcp-flags SYN,RST,ACK SYN -j ACCEPT #iptables -A INPUT -p tcp -m tcp --dport 29901 --tcp-flags SYN,RST,ACK SYN -j ACCEPT #iptables -A INPUT -p tcp -m tcp --dport 29920 --tcp-flags SYN,RST,ACK SYN -j ACCEPT #iptables -A INPUT -p udp -m udp -m multiport --ports 5120:5129 -j ACCEPT #iptables -A INPUT -p udp -m udp --dport 6500 -j ACCEPT #iptables -A INPUT -p udp -m udp --dport 27900 -j ACCEPT #iptables -A INPUT -p udp -m udp --dport 27901 -j ACCEPT #iptables -A INPUT -p udp -m udp --dport 29910 -j ACCEPT # Log everything else: What's Windows' latest exploitable vulnerability? iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT" # set a sane policy: everything not accepted > /dev/null iptables -P INPUT DROP iptables -P FORWARD DROP iptables -P OUTPUT DROP iptables -A INPUT -p icmp --icmp-type echo-request -j DROP # be verbose on dynamic ip-addresses (not needed in case of static IP) echo 2 > /proc/sys/net/ipv4/ip_dynaddr # disable ExplicitCongestionNotification - too many routers are still # ignorant echo 0 > /proc/sys/net/ipv4/tcp_ecn #ping death echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all # If you are frequently accessing ftp-servers or enjoy chatting you might # notice certain delays because some implementations of these daemons have # the feature of querying an identd on your box for your username for # logging. Although there's really no harm in this, having an identd # running is not recommended because some implementations are known to be # vulnerable. # To avoid these delays you could reject the requests with a 'tcp-reset': #iptables -A INPUT -p tcp --dport 113 -j REJECT --reject-with tcp-reset #iptables -A OUTPUT -p tcp --sport 113 -m state --state RELATED -j ACCEPT # To log and drop invalid packets, mostly harmless packets that came in # after netfilter's timeout, sometimes scans: #iptables -I INPUT 1 -p tcp -m state --state INVALID -j LOG --log-prefix \ "FIREWALL:INVALID" #iptables -I INPUT 2 -p tcp -m state --state INVALID -j DROP # End /bin/firewall-start Active ruleset: bash-4.1# iptables -L -n -v Chain INPUT (policy DROP 38 packets, 2228 bytes) pkts bytes target prot opt in out source destination 0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0 844 542K ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 38 2228 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 LOG flags 0 level 4 prefix `FIREWALL:INPUT' 0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 38 2228 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 LOG flags 0 level 4 prefix `FIREWALL:INPUT' Chain FORWARD (policy DROP 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain OUTPUT (policy DROP 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 1158 111K ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 Active ruleset: (after editing iptables into below sugested form) bash-4.1# iptables -L -n -v Chain INPUT (policy DROP 2567 packets, 172K bytes) pkts bytes target prot opt in out source destination 49 4157 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0 412K 441M ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 2567 172K LOG all -- * * 0.0.0.0/0 0.0.0.0/0 LOG flags 0 level 4 prefix `FIREWALL:INPUT' 0 0 DROP icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmp type 8 Chain FORWARD (policy DROP 0 packets, 0 bytes) pkts bytes target prot opt in out source destination Chain OUTPUT (policy ACCEPT 312K packets, 25M bytes) pkts bytes target prot opt in out source destination ping and syslog simultaneous screenshots from phone (pinger) and from laptop (being pinged) http://dl.dropbox.com/u/4160051/slckwr/pingfrom%20mobile.jpg http://dl.dropbox.com/u/4160051/slckwr/tailsyslog.jpg

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  • What ORMs work well with Scala?

    - by Clinton R. Nixon
    I'm about to write a Scala command-line application that relies on a MySQL database. I've been looking around for ORMs, and am having trouble finding one that will work well. The Lift ORM looks nice, but I'm not sure it can be decoupled from the entire Lift web framework. ActiveObjects also looks OK, but the author says that it may not work well with Scala. I'm not coming to Scala from Java, so I don't know all the options. Has anyone used an ORM with Scala, and if so, what did you use and how well did it work?

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  • How to get current date and time from DB using SQLAlchemy

    - by bluish
    I need to retrieve what's the current date and time for the database I'm connected with SQLAlchemy (not date and time of the machine where I'm running Python code). I've seen this functions, but they don't seem to do what they say: >>> from sqlalchemy import * >>> print func.current_date() CURRENT_DATE >>> print func.current_timestamp() CURRENT_TIMESTAMP Moreover it seems they don't need to be binded to any SQLAlchemy session or engine. It makes no sense... Thanks!

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  • How to deal with databases for websites written in Java, more specifically Wicket?

    - by John
    Hi there. I'm new to website development using Java but I've got started with Wicket and make a little website. I'd like to expand on what I've already made (a website with a form, labels and links) and implement database connectivity. I've looked at a couple of examples, in example Mystic Paste, and I see that they're using Hibernate and Spring. I've never touched Hibernate or Spring before and to be honest the heavy use of annotations scare me a little bit as I haven't really made use of them before, with the exception of supressing warnings and overriding. At this point I have one Connection object which I set up in the WebApplication class upon initialization. I then retrieve this connection object whenever I need to perform queries. I don't know if this is a bad approach or not for a production web application. All help is greatly appreciated.

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  • Second level cache for java web app and its alternatives

    - by EugeneP
    Between the transitions of the web app I use a Session object to save my objects in. I've heard there's a program called memcached but there's no compiled version of it on the site, besides some people think there are real disadvantages of it. Now I wanna ask you. What are alternatives, pros and cons of different approaches? Is memcached painpul for sysadmins to install? Is it difficult to embed it to the existing infrastructure from the perspective of a sysadmin? What about using a database to hold temporary data between web app transitions? Is it a normal practice?

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  • Any tips of how to handle hierarchical trees in relational model?

    - by George
    Hello all. I have a tree structure that can be n-levels deep, without restriction. That means that each node can have another n nodes. What is the best way to retrieve a tree like that without issuing thousands of queries to the database? I looked at a few other models, like flat table model, Preorder Tree Traversal Algorithm, and so. Do you guys have any tips or suggestions of how to implement a efficient tree model? My objective in the real end is to have one or two queries that would spit the whole tree for me. With enough processing i can display the tree in dot net, but that would be in client machine, so, not much of a big deal. Thanks for the attention

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  • High performance querying - Suggestions please

    - by Alex Takitani
    Supposing that I have millions of user profiles, with hundreds of fields (name, gender, preferred pet and so on...). You want to make searches on profiles. Ex.:All profiles that has age between x and y, loves butterflies, hates chocolate.... With database would you choose? Suppose that You have a Facebook like load. Speed is a must. Open Source preferred. I've read a lot about Cassandra, HBase, Mongo, Mysql... I just can't decide.....

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