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• Should a primary key be immutable?

  - by Vincent Malgrat

  A recent question on stackoverflow provoked a discussion about the immutability of primary keys. I had thought that it was a kind of rule that primary keys should be immutable. If there is a chance that some day a primary key would be updated, I thought you should use a surrogate key. However it is not in the SQL standard and some RDBMS' "cascade update" feature allows a primary key to change. So my question is: is it still a bad practice to have a primary key that may change ? What are the cons, if any, of having a mutable primary key ?

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• implementing dynamic query handler on historical data

  - by user2390183

  EDIT : Refined question to focus on the core issue Context: I have historical data about property (house) sales collected from various sources in a centralized/cloud data source (assume info collection is handled by a third party) Planning to develop an application to query and retrieve data from this centralized data source Example Queries: Simple : for given XYZ post code, what is average house price for 3 bed room house? Complex: What is estimated price for an house at "DD,Some Street,XYZ Post Code" (worked out from average values of historic data filtered by various characteristics of the house: house post code, no of bed rooms, total area, and other deeper insights like house building type, year of built, features)? In addition to average price, the application should support other property info ** maximum, or minimum price..etc and trend (graph) on a selected property attribute over a period of time**. Hence, the queries should not enforce the search based on a primary key or few fixed fields In other words, queries can be What is the change in 3 Bed Room house price (irrespective of location) over last 30 days? What kind of properties we can get for X price (irrespective of location or house type) The challenge I have is identifying the domain (BI/ Data Analytical or DB Design or DB Query Interface or DW related or something else) this problem (dynamic query on historic data) belong to, so that I can do further exploration My findings so far I could be wrong on the following, so please correct me if you think so I briefly read about BI/Data Analytics - I think it is heavy weight solution for my problem and has scalability issues. DB Design - As I understand RDBMS works well if you know Data model at design time. I am expecting attributes about property or other entity (user) that am going to bring in, would evolve quickly. hence maintenance would be an issue. As I am going to have multiple users executing query at same time, performance would be a bottleneck Other options like Graph DB (http://www.tinkerpop.com/) seems to be bit complex (they are good. but using those tools meant for generic purpose, make me think like assembly programming to solve my problem ) BigData related solution are to analyse data from multiple unrelated domains So, Any suggestion on the space this problem fit in ? (Especially if you have design/implementation experience of back-end for property listing or similar portals)

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• Data Synchronization in mobile apps - multiple devices, multiple users

  - by ProgrammerNewbie

  I'm looking into building my first mobile app. One of the core features of the application is that multiple devices/users will have access to the same data -- and all of them will have CRUD rights. I believe the architecture should involve a central server where all the data is stored. The devices will use an API to interact with the server to perform its data operations (e.g. adding a record, editing a record, deleting a record). I imagine a scenario where synchronizing the data will become a problem. Assume the application should work when it is not connected to the Internet, and thus cannot communicate with this central server. So: User A is offline and edits record #100 User B is offline and edits record #100 User C is offline and deletes record #100 User C goes online (presumably, record #100 should get deleted on the server) User A and B goes online, but the records they edited no longer exist All sorts of scenarios similar to the above can come up. How is this generally handled? I plan to use MySQL, but am wondering if it's not appropriate for such a problem.

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• Implementing new required feature after software release

  - by TiagoBrenck

  Fake Scenario There is a software that was released 1 year ago. The software is to map and register all kind of animals on our planet. When the software was released, the client only needed to know the scientific name of the animal, a flag if it is in risk of extinction and a scale of dangerous(that is a fake software and specification, I don't want to discuss this here). There are already 100.000 animals records saved on DB. New Feature One year later, the client wants a new feature. It is really important to him to know the animals classes, and this is a required field. So he asks me to put a field to input the animal class, and this field is required. Or maybe where this animal was discovered. Problem I have already 100.000 recorded animals without a class or where it was discovered, but I need to insert a new column to storage this information and this column can't be null. I don't have a default value for this situation (there isn't a default animal class or where it was discovered). I don't want to keep the requirement rule only on my software, my DB must have this requirement too(I like to keep business rules on DB too). What are the alternatives to solve this situation? I am on a situation that this new feature cannot be previewed or reviewed for the existing records. The time already passed and I can't go back on time to get it

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• What is the best way to work with large databases in Java depending on context?

  - by user19000

  We are trying to figure out the best practice for working with very large DBs in Java. What we do is a kind of BI (business Intelligence), i.e analyzing very large DBs, and using them to create intermediate DBs that represent intelligent knowledge of the DBs. We are currently using JDBC, and just preforming queries using a ResultSet. As more and more data is being created, we are wondering whether more appropriate ways exist for parsing and manipulating these large DBs: We need to support 'chunk' manipulation and not an entire DB at once(e.g. limit in JDBC, very poor performance) We do not need to be constantly connected since we are just pulling results and creating new tables of our own. We want to understand JDBC alternatives, with respect to advantages and disadvantages. Whether you think JDBC is the way to go or not, what are the best practices to go by depending on context (e.g. for large DBs queried in chunks)?

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• choosing the right RAID level for PostgresQL database

  - by Sergey

  Hi, I got an disk array appliance of 8 disks 1T each (UltraStor RS8IP4). It will be used solely by PostgresQL database and I am trying to choose the best RAID level for it. The most priority is for read performance since we operate large data sets (tables, indexes) and we do lots of searches/scans. With the old disks that we have now the most slowdowns happen on SELECTs. Fault tolerance is less important, it can be 1 or 2 disks. Space is the least important factor. Even 1T will be enough. Which RAID level would you recommend in this situation. The current options are 60, 50 and 10, but probably other options can be even better.

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• The Mindset of the Enterprise DBA: Creating and Applying Standards to Our Work

  Although many professions, such as pilots, surgeons and IT administrators, require judgement and skill, they also require the ability to do many repeated standard procedures in a consistent and methodical manner. These procedures leave little room for creativity since they must be done right, and in the right order. For DBAs, standardization involves providing and following checklists, notes and instructions so that the results are predictable, correct and easy to maintain

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• TechEd 2010 Followup

  - by AllenMWhite

  Last week I presented a couple of sessions at Tech Ed NA in New Orleans. It was a great experience, even though my demos didn't always work out as planned. Here are the sessions I presented: DAT01-INT Administrative Demo-Fest for SQL Server 2008 SQL Server 2008 provides a wealth of features aimed at the DBA. In this demofest of features we'll see ways to make administering SQL Server easier and faster such as Centralized Data Management, Performance Data Warehouse, Resource Governor, Backup Compression...(read more)

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• EAV - is it really bad in all scenarios?

  - by Giedrius

  I'm thinking to use EAV for some of the stuff in one of the projects, but all questions about it in stackoverflow end up to answers calling EAV an anti pattern. But I'm wondering, if is it that wrong in all cases? Let's say shop product entity, it has common features, like name, description, image, price, etc., that take part in logic many places and has (semi)unique features, like watch and beach ball would be described by completely different aspects. So I think EAV would fit for storing those (semi)unique features? All this is assuming, that for showing product list, it is enough info in product table (that means no EAV is involved) and just when showing one product/comparing up to 5 products/etc. data saved using EAV is used. I've seen such approach in Magento commerce and it is quite popular, so may be there are cases, when EAV is reasonable?

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• Lingering database-connections from Feng Office

  - by Bobby

  I've installed Feng Office on our main server which is working perfectly so far. Unfortunately it seems like there's a problem with the connection to the MySQL-Database. While the connection itself works fine, it's the reuse/pooling of connections which seems to be bugged. There are lingering/sleeping connections to the server from Feng Office which won't close and don't get reused after some time (120 seconds). Of course those lingering processes/connections are piling up pretty fast. I've found a thread at the forums about this behavior, but the suggested fix is already applied (by default). I'm sure this is just a configuration issue, but I'm a little clue less because Feng is besides a MediaWiki, a DokuWiki and homebrewed PHP applications the only one with this issue. The setup is a Microsoft Windows 2003 Server with MySQL 5.0.26 and Apache 2.2. Where can I start looking for clues why this is happening and how do I get rid of lingering MySQL-Connections?

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• Master Data Management

  - by Logicalj

  I am looking for a very flexible, easy to integrate and dynamic application with as many features as possible for Master Data Management. As Master Data Management is used to Manage Operational Data, Analytical Data and Master Data so, I want guidance about "What is exactly expected from Master Data Management and What are the Basic and Challenging Scenarios to be covered or resolved in Master Data Management". Please guide me with all the possible aspects of Master Data Management like Data Cleansing, Data Management and Start Data Analyzing, etc.

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• MySQLwith mutiple threads and processes

  - by Abhan

  I'm developing a telecom messaging platform in C, and I'm going to need multiple processes to be working with MySQL DB. How can I make two processes read/write to/from a Mysql DB and, if/when one of them goes down, get the other to seamlessly take over the work until the dead process gets back to work? I was thinking/googling some options and am stuck in place where I don't know which one to choose. What I think so far is that table lock is not the best option to go for, as it will stall the other process until the table is unlocked. The other option is to use row-level locks or manual locks, but I can't find the best way to do it.

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• Pommes für alle?

  - by A&C Redaktion

  Ja, liebe Partner - wie Sie sich und Ihre Kunden vor ungewollten Zugriffen schützen, dazu gibt es nun einen charmanten Video-Clip, der in nur einer Minute den Sprung von den Pommes zur Oracle Access Management Suite schafft. Eine spielerische Hinführung zum Thema Zugriffsrechte, die sich mit ihrem gelungenen Überraschungseffekt auch hervorragend im Kundengespräch nutzen lässt. Gleich anschauen, „gefällt mir“ klicken - weiterempfehlen und verlinken! Weiterführende Informationen zum Access Management Portfolio sind online verfügbar:http://www.oracle.com/us/products/middleware/identity-management/access-management/overview/index.htmlAuch auf die derzeit am Markt besprochenen Themen zu Mobile&Social hat Oracle eine neue Antwort:http://www.oracle.com/technetwork/middleware/id-mgmt/overview/oamms-1696162.htmlEin weiteres sehenswertes Video finden Sie hier:http://www.oracle.com/us/products/middleware/identity-management/oiam/overview/index.html

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• Upload large database SQL file

  - by Devy

  I've a database of more than 20Gb of size on my hard disk. What is the best way to upload it with the least (money) load possible on the server? - I'm on Windows 7. - I have FTP and SSH access on the server. I avoid using FTP because my connection cuts off a lot, I can't imagine I re-upload again the file after failing on 99%. I found some tools that split the large .sql file to small .sql files, but they didn't mention how to gather these files again into one file. Another way is to archive the big .sql file to .rar with -v option, upload them through FTP then unpack them. But unpacking will also cost, right? I know it will cost in any cases, but any best practice will be strongly appreciated.

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• MySQL with mutiple threads and processes

  - by Abhan

  I'm developing a telecom messaging platform in C, and I'm going to need multiple processes to be working with MySQL DB. How can I make two processes read/write to/from a Mysql DB and, if/when one of them goes down, get the other to seamlessly take over the work until the dead process gets back to work? I was thinking/googling some options and am stuck in place where I don't know which one to choose. What I think so far is that table lock is not the best option to go for, as it will stall the other process until the table is unlocked. The other option is to use row-level locks or manual locks, but I can't find the best way to do it.

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• Saving all hits to a web app

  - by bevanb

  Are there standard approaches to persisting data for every hit that a web app receives? This would be for analytics purposes (as a better alternative to log mining down the road). Seems like Redis would be a must. Is it advisable to also use a different DB server for that table, or would Redis be enough to mitigate the impact on the main DB? Also, how common is this practice? Seems like a no brainer for businesses who want to better understand their users, but I haven't read much about it.

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• Alternative to TOP in SQL Server and Oracle.

  SELECT TOP 5 * FROM EMP ORDER BY SALARY; Above query works in SQL Server. This returns top 5 employees. The problem with this query is it doesn't work with Oracle. In Oracle you would need to write the query as follows. SELECT * FROM EMP WHERE ROWNUM<=5 ORDER BY SALARY If you are looking for a query which runs in both Oracle and SQL Server. Please use below one. select * from (SELECT row_number() over( ORDER by SALARY) as rank, EMP.* FROM EMP) s1 where s1.rank <= 5; span.fullpost {display:none;}

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• Need advice concerning Feature Based Development when knowledge DB is involved

  - by voroninp

  We develop BackOffice application which is used to edit our knowledge DB. Now our main product's development team is shifting to the feature based development and we need to support several DB's with not identical data schemes. (DS changes slightly from DB to DB) The information from knowledge Db is extracted by the script and then is distributed to the clients. We also need to support merging these DB's. We now analyze pros and cons of different approaches. We discuss this one: One working DB (WDB) with one DB for each feature branch (FDB). The approved data is moved from WDB to FDB. So we need to support only one script for each branch. This script will extract data from corresponding FDB. Nevertheless we are to code the differences between FDBs and WDB manually. May be some automatic mapping tools exist? I also wish to know whether classic solutions to the alike problems already exist. Can anyone share the best practices for this case?

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• Multitenancy in SQL Azure

  - by cibrax

  If you are building a SaaS application in Windows Azure that relies on SQL Azure, it’s probably that you will need to support multiple tenants at database level. This is short overview of the different approaches you can use for support that scenario, A different database per tenant A new database is created and assigned when a tenant is provisioned. Pros Complete isolation between tenants. All the data for a tenant lives in a database only he can access. Cons It’s not cost effective. SQL Azure databases are not cheap, and the minimum size for a database is 1GB.  You might be paying for storage that you don’t really use. A different connection pool is required per database. Updates must be replicated across all the databases You need multiple backup strategies across all the databases Multiple schemas in a database shared by all the tenants A single database is shared among all the tenants, but every tenant is assigned to a different schema and database user. Pros You only pay for a single database. Data is isolated at database level. If the credentials for one tenant is compromised, the rest of the data for the other tenants is not. Cons You need to replicate all the database objects in every schema, so the number of objects can increase indefinitely. Updates must be replicated across all the schemas. The connection pool for the database must maintain a different connection per tenant (or set of credentials) A different user is required per tenant, which is stored at server level. You have to backup that user independently. Centralizing the database access with store procedures in a database shared by all the tenants A single database is shared among all the tenants, but nobody can read the data directly from the tables. All the data operations are performed through store procedures that centralize the access to the tenant data. The store procedures contain some logic to map the database user to an specific tenant. Pros You only pay for a single database. You only have a set of objects to maintain and backup. Cons There is no real isolation. All the data for the different tenants is shared in the same tables. You can not use traditional ORM like EF code first for consuming the data. A different user is required per tenant, which is stored at server level. You have to backup that user independently. SQL Federations A single database is shared among all the tenants, but a different federation is used per tenant. A federation in few words, it’s a mechanism for horizontal scaling in SQL Azure, which basically uses the idea of logical partitions to distribute data based on certain criteria. Pros You only have a single database with multiple federations. You can use filtering in the connections to pick the right federation, so any ORM could be used to consume the data. Cons There is no real isolation at that database level. The isolation is enforced programmatically with federations.

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• User input and Automated input seperation

  - by tpaksu

  I have a mysql db and I have an automation script which modifies the data inside once a day. And, these columns may have changed by an user manually. What is the best approach to make the system only update the automated data, not the manually edited ones? I mean yes, flagging the cell which is manually edited is one way to do it, but I want to know if there's another way to accomplish this? Just curiosity.

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• Creating encrypted database for work

  - by Baldur

  My boss posed this problem to me: Encrypted: We need an encrypted database for miscellanious passwords we use at work that are currently only in people's head. Easily accessable: Someone needs to be able to quickly access specific passwords, possibly at hectic moments. This requires any sort of public key management (keeping it on a USB key in a sealed envelope?) to be relatively easy. Access control: The system should have groups of passwords where only specific people have access to specific groups. Recoverability: We need to make sure passwords from one group aren't lost even if the only users with direct access quit or pass away—hence we need some way where (for example) any two members of senior management may override the system (see the treshold link below) and retrieve all the passwords with their key. The first thing that jumped into my mind was some form of threshold and asymmetric cryptography but I don't want to reinvent the wheel, are there any solutions for this? Any software should preferrably be free and open-source.

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• Database for heat tolerances of various cables?

  - by I. F.

  Is there any kind of unified database of heat tolerances for networking cables? I've been setting up a number of home/small office networks lately and as a mostly-amateur I could really use some information on what is safe to run behind a radiator, next to a steam pipe, etc. The question I'm up against at the moment is: Can I run normal RJ11 phone line cable (from DSL modem to phone jack) behind a steam radiator without risking a fire? Unlike cat5, I could not find published standards for these, so I'm turning to experts with more experience. This is a cut-rate show. Do I go out and buy more cabling, and if so which, or use the spare that I have?

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• non-volatile virtual memory for C++ containers

  - by arieberman

  Is there a virtual memory management process that would allow a program to use the standard container structures and classes, but retain these structures and their data when the program is not running (or being used), for use by the program at a later time? This should be possible, but can it be done without changing the source code and its (container) declarations? Is there a standard way of doing this?

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• Scanning the Error Log with PowerShell

  - by AllenMWhite

  One of the most important things you can do as a DBA is to keep tabs on the errors reported in the error log, but there's a lot of information there and sometimes it's hard to find the 'good stuff'. You can open the errorlog file directly in a text editor and search for errors but that gets tedious, and string searches generally return just the lines with the error message numbers, and in the error log the real information you want is in the line after that. PowerShell 2.0 introduced a new cmdlet...(read more)

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• Database or website of kernel config files ?

  - by Kami

  I've experienced some kernel panic after trying to compile gentoo kernel for a Sun UltraSPARC T5120 Server. The kernel panic came from a missing support for the SAS disk controller in the menu config. I've wasted so much time because I had no clue about the hardware I was using. I know that the kernel config depends on what you plan to do with your machine but I want to have a configuration file that at least match my hardware ! Is there a website or database that provides menuconfig's kernel configuration files for known or branded hardware like Dell Server or Apple computers ?

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