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  • How to achieve high availability?

    - by tanyehzheng
    My boss wants to have a system that takes into concern of continent wide catastrophic event. He wants to have two servers in US and two servers in Asia (1 login server and 1 worker server in each continent). In the event that earthquake breaks the connection between the two continents, both should work alone. When the connection is revived, they should sync each other back to normal. External cloud system not allowed as he has no confidence. The system should take into account of scalability which means addition of new servers should be easy to configure. The servers should be load balanced. The connection between the servers should be very secure(encrypted and send through SSL although SSL takes care of encryption). The system should let one and only one user log in with one account. (beware of latency between continent and two users sharing account may reach both login server at the same time) Please help. I'm already at the end of my wit. Thank you in advance.

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  • Design for tagging system in GAE-J

    - by tempy
    I need a simple tagging system in GAE-J. As I see it, the entity that is being tagged should have a collection of keys referring to the tags with which it's associated. A tag entity should simply contain the tag string itself, and a collection of keys pointing to the entities associated with the tag. When an entity's list of tags is altered, the system will create a new tag if the tag is unknown, and then append the entity's key to that tag's key collection. If the tag already exists, then the entity's key is simply appended to the tag's key collection. This seems relatively straight-forward and uncontroversial to me, but I would like some feedback on this design, just to be sure.

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  • Which Oracle table uses a sequence?

    - by Jaú
    Having a sequence, I need to find out which table.column gets its values. As far as I know, Oracle doesn't keep track of this relationship. So, looking up for the sequence in source code would be the only way. Is that right? Anyone knows of some way to find out this sequence-table relationship?

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  • BI with Django?

    - by Helmut
    Is there a way to develop Bi (Business Intelligence) solutions with Django? Therefore it should be possible to define models with more than one Datasource. Is anybody out there who has experienced BI with Django? How could it work ?

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  • Calling data from different model in Rails

    - by Danny McClelland
    Hi Everyone, I need to be able to call data from a different model - not just one field, but any of them. At the moment I have the following models: kase person company party I can call information from the company to the kase and from the person to the kase using this: <li>Client Company Address: <span class="address"><%=h @kase.company.companyaddress %></span></li> <li>Case Handler: <span><%=h @kase.person.personname %></span></li> Those two work, however if I add the following: <li>Client Company Fax: <span><%=h @kase.company.companyfax %></span></li> <li>Case Handler Tel: <span><%=h @kase.person.personmobile %></span></li> <li>Case Handler Email: <span><%=h @kase.person.personemail %></span></li> Any idea whats wrong? Thanks, Danny EDIT: I get the following error message: NoMethodError in Kases#show Showing app/views/kases/show.html.erb where line #37 raised: You have a nil object when you didn't expect it! The error occurred while evaluating nil.personname The lines that are noted are as follows: 34: <div id="clientinfo_showhide" style="display:none"> 35: <li>Client Company Address: <span class="address"><%=h @kase.company.companyaddress %></span></li> 36: <li>Client Company Fax: <span><%=h @kase.company.companyfax %></span></li> 37: <li>Case Handler: <span><%=h @kase.person.personname %></span></li> 38: <li>Case Handler Tel: <span><%=h @kase.person.personmobile %></span></li> 39: <li>Case Handler Email: <span><%=h @kase.person.personemail %></span></li> 40: </div> The model for the kase is as follows: class Kase belongs_to :company # foreign key: company_id belongs_to :person # foreign key in join table The model for the person is as follows: class Person has_many :kases # foreign key in join table belongs_to :company The model for the company is as follows: class Company has_many :kases has_many :people def to_s; companyname; end Hope this helps!

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  • Retrieving all objects in code upfront for performance reasons

    - by ming yeow
    How do you folks retrieve all objects in code upfront? I figure you can increase performance if you bundle all the model calls together? This makes for a bigger deal, especially if your DB cannot keep everything in memory def hitDBSeperately { get X users ...code get Y users... code get Z users... code } Versus: def hitDBInSingleCall { get X+Y+Z users code for X code for Y... }

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  • MS Query Analizer/Management Studio replacement?

    - by kprobst
    I've been using SQL Server since version 6.5 and I've always been a bit amazed at the fact that the tools seem to be targeted to DBAs rather than developers. I liked the simplicity and speed of the Query Analizer for example, but hated the built-in editor, which was really no better than a syntax coloring-capable Notepad. Now that we have Management Studio the management part seems a bit better but from a developer standpoint the tools is even worse. Visual Studio's excellent text editor... without a way to customize keyboard bindings!? Don't get me started on how unusable is the tree-based management hierarchy. Why can't I re-root the tree on a list of stored procs for example the way the Enterprise Manager used to allow? Now I have a treeview that needs to be scrolled horizontally, which makes it eminently useless. The SQL server support in Visual Studio is fantastic for working with stored procedures and functions, but it's terrible as a general ad hoc data query tool. I've tried various tools over the years but invariably they seem to focus on the management side and shortchange the developer in me. I just want something with basic admin capabilities, good keyboard support and requisite DDL functionality (ideally something like the Query Analyzer). At this point I'm seriously thinking of using vim+sqlcmd and a console... I'm that desperate :) Those of you who work day in and day out with SQL Server and Visual Studio... do you find the tools to be adequate? Have you ever wished they were better and if you have found something better, could you share please? Thanks!

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  • Seeking a GUI auto-format feature for T-SQL

    - by dvanaria
    Is there a freely available GUI tool that will allow interaction with Microsoft SQL Server (via T-SQL) that provides an auto-format feature? I constantly find myself writing queries in SQL Query Analyzer (Microsoft’s standard GUI tool for T-SQL) and cutting/pasting the whole thing into SQLyog (a GUI tool for MySQL), where I can press F12 and have it reformatted into an easily readable, industry standard format. I then cut/paste this back into Query Analyzer to execute. I do this all the time at work and haven’t been able to find an alternative. I realize that SQLyog is no longer free software, but what I’m looking for is a specific alternative to a MS SQL Server interface (with auto-formatting). Thanks in advance for your help.

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  • Using Entity Framework, how do I specify a sort on a navagation property?

    - by Jared
    I have two tables: [Category], [Item]. They are connected by a join table: [CategoryAndItem]. It has two primary key fields: [CategoryKey], [ItemKey]. Foreign keys exist appropriately and Entity has no problem pulling this in and creating the correct navigation properties that connect the entity objects. Basically each category can have multiple items, and items can be in multiple categories. The problem is that the order of items is specified per category, so that a particular item might be third in one category but fifth in another. In the past, I have added a [Sequence] field to the join table and modified the stored procedure to handle it. But since Entity is replacing my stored procedures, I need to figure out how to make Entity handle the sequence. Any suggestions?

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  • Hierarchical Data in MySQL is as fast as XML to retrieve?

    - by ajsie
    i've got a list of all countries - states - cities (- subcities/villages etc) in a XML file and to retrieve for example a state's all cities it's really quick with XML (using xml parser). i wonder, if i put all this information in mysql, is retrieving a state's all cities as fast as with XML? cause XML is designed to store hierarchical data while relational databases like mysql are not. the list contains like 500 000 entities. so i wonder if its as fast as XML using either of: Adjacency list model Nested Set model And which one should i use? Cause (theoretically) there could be unlimited levels under a state (i heard that adjacency isn't good for unlimited child-levels). And which is fastest for this huge dataset? Thanks!

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  • How can I view live MySQL queries?

    - by barfoon
    Hey all, I am just wondering if its possible to trace MySQL queries on my linux server as they happen? For example I'd love to set up some sort of listener, then request a web page and view all of the queries the engine executed, or just view all of the queries being run on a production server. Are there tools to do this? Thank you,

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  • Does Ruby on Rails "has_many" array provide data on a "need to know" basis?

    - by Jian Lin
    On Ruby on Rails, say, if the Actor model object is Tom Hanks, and the "has_many" fans is 20,000 Fan objects, then actor.fans gives an Array with 20,000 elements. Probably, the elements are not pre-populated with values? Otherwise, getting each Actor object from the DB can be extremely time consuming. So it is on a "need to know" basis? So does it pull data when I access actor.fans[500], and pull data when I access actor.fans[0]? If it jumps from each record to record, then it won't be able to optimize performance by doing sequential read, which can be faster on the hard disk because those records could be in the nearby sector / platter layer -- for example, if the program touches 2 random elements, then it will be faster just to read those 2 records, but what if it touches all elements in random order, then it may be faster just to read all records in a sequential way, and then process the random elements. But how will RoR know whether I am doing only a few random elements or all elements in random?

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  • SQLAlchemy - relationship limited on more than just the foreign key

    - by Marian
    I have a wiki db layout with Page and Revisions. Each Revision has a page_id referencing the Page, a page relationship to the referenced page; each Page has a all_revisions relationship to all its revisions. So far so common. But I want to implement different epochs for the pages: If a page was deleted and is recreated, the new revisions have a new epoch. To help find the correct revisions, each page has a current_epoch field. Now I want to provide a revisions relation on the page that only contains its revisions, but only those where the epochs match. This is what I've tried: revisions = relationship('Revision', primaryjoin = and_( 'Page.id == Revision.page_id', 'Page.current_epoch == Revision.epoch', ), foreign_keys=['Page.id', 'Page.current_epoch'] ) Full code (you may run that as it is) However this always raises ArgumentError: Could not determine relationship direction for primaryjoin condition ...`, I've tried all I had come to mind, it didn't work. What am I doing wrong? Is this a bad approach for doing this, how could it be done other than with a relationship?

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  • Any disadvantages to this tagging approach

    - by donpal
    I have a table of tags ID tag --- ------ 1 tagt 2 tagb 3 tagz 4 tagn In my items table, I'm using those tags in serialized format, comma delimited ID field1 tags ---- ------ ----- 1 value1 tagt,tagb 2 value2 tagb 3 value3 tagb,tagn 4 value4 When I need to find items that have this tag, I plan to deserialize the tags. But I'm not actually sure how to do it, and if it's better to have a third table for associations instead between the tags and the items.

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  • Question About DateCreated and DateModified Columns - SQL Server

    - by user311509
    CREATE TABLE Customer ( customerID int identity (500,20) CONSTRAINT . . dateCreated datetime DEFAULT GetDate() NOT NULL, dateModified datetime DEFAULT GetDate() NOT NULL ); When i insert a record, dateCreated and dateModified gets set to default date/time. When i update/modify the record, dateModified and dateCreated remains as is? What should i do? Obviously, i need to dateCreated value to remain as was inserted the first time and dateModified keeps changing when a change/modification occurs in the record fields. In other words, can you please write a sample quick trigger? I don't know much yet...

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  • Systems design question: DB connection management in load-balanced n-tier

    - by aoven
    I'm wondering about the best approach to designing a DB connection manager for a load-balanced n-tier system. Classic n-tier looks like this: Client -> BusinessServer -> DBServer A load-balancing solution as I see it would then look like this: +--> ... +--+ +--> BusinessServer +--+--> SessionServer --+ Client -> Gateway --+--> BusinessServer +--| +--> DBServer +--> BusinessServer +--+--------------------+ +--> ... +--+ As pictured, the business server component is being load-balanced via multiple instances, and a hardware gateway is distributing the load among them. Session server probably needs to be situated outside the load-balancing array, because it manages state, which mustn't be duplicated. Barring any major errors in design so far, what is the best way to implement DB connection management? I've come up with a couple of options, but there may be others I'm not aware of: Introduce a new Broker component between the DBServer and the other components and let it handle the DB connections. The upside is that all the connections can be managed from a single point, which is very convenient. The downside is that now there is an additional "single point of failure" in the system. Other components must go through it for every request that involves DB in some way, which also makes this a bottleneck. Move the DB connection management into BusinessServer and SessionServer components and let each handle its own DB connections. The upside is that there is no additional "single point of failure" or bottleneck components. The downside is that there is also no control over possible conflicts and deadlocks apart from what DBServer itself can provide. What else can be done? FWIW: Technology is .NET, but none of the vendor-specific stacks are used (e.g. no WCF, MSMQ or the like).

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  • Ora-01000 - maximum open cursors exceeded error

    - by PeteDaMeat
    I am receiving the following error message within my Delphi/Oracle application "ora-01000 - maximum open cursors exceeded". The code is as follows: begin for i := 0 to 150 do begin with myADOQuery do begin SQL.Text := 'DELETE FROM SOMETABLE'; ExecSQL; -- from looking at V$OPEN_CURSOR a new cursor is added on each iteration for the session Close; -- thought this would close the cursor but doesn't end; end; end; I'm aware I can resolve the problem by simply increasing the number of OPEN_CURSORS parameters, however, I would rather find a solution whereby the cursor is closed after the query is executed. Any ideas? Delphi 2006 BDS Oracle 10g

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  • MySQL Query order by numer of rows?

    - by Clemens
    hi, i have a mysql table for votes. there's am id, a project_id and a vote field (which is 1 if a specific project is voted). now i want to generate a ranking from those entries. is there a way to get the number of votes for each project_id and automatically sort the entries by the number of TRUE votes of a project with a single mysql query? Or do you know a php way? e.g. ID - Project ID - Vote 1 - 2 - 1 2 - 2 - 1 3 - 1 - 1 == Project Nr. 2 has 2 Votes Project Nr. 1 has 1 Vote Thanks in advance!

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  • Version of SQLite used in Android?

    - by Eno
    Reason: Im wondering how to handle schema migrations. The newer SQLite versions support an "ALTER TABLE" SQL command which would save me having to copy data, drop the table, recreate table and re-insert data.

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