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  • atomic writes to ehcache

    - by Jacques René Mesrine
    Context I am storing a java.util.List inside ehcache. Key(String) --> List<UserDetail> The ordered List contains a Top 10 ranking of my most active users. Problem Concurrent 3rd party clients might be requesting for this list. I have a requirement to be as current as possible with regards to the ranking. Thus if the ranking is changed due the activities of users, the ordered List in the cache must not be left stale for very long. Once I've recalculated a new List, I want to replace the one in cache immediately. Consider a busy scenario whereby multiple concurrent clients are requesting for the ranking; how can I replace the cache item in an fashion such that: Clients can continue to pull a possibly stale snapshot. They should never get a null value. There will only be 1 server thread that writes to the cache.

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  • How to generate a unique hash for a URL ?

    - by Jacques René Mesrine
    Given these two images from twitter. http://a3.twimg.com/profile_images/130500759/lowres_profilepic.jpg http://a1.twimg.com/profile_images/58079916/lowres_profilepic.jpg I want to download them to local filesystem & store them in a single directory. How shall I overcome name conflicts ? In the example above, I cannot store them as *lowres_profilepic.jpg*. My design idea is treat the URLs as opaque strings except for the last segment. What algorithms (implemented as f) can I use to hash the prefixes into unique strings. f( "http://a3.twimg.com/profile_images/130500759/" ) = 6tgjsdjfjdhgf f( "http://a1.twimg.com/profile_images/58079916/" ) = iuhd87ysdfhdk That way, I can save the files as:- 6tgjsdjfjdhgf_lowres_profilepic.jpg iuhd87ysdfhdk_lowres_profilepic.jpg I don't want a cryptographic algorithm as it this needs to be a performant operation.

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  • For a primary key of an integral type, why is it important to avoid gaps ?

    - by Jacques René Mesrine
    I am generating a surrogate key for a table & due to my hi/lo algorithm, everytime you reboot/restart the machine, gaps may appear. T1: current hi = 10000000 (sequence being dished out .. 1 to 100) Assume that current sequence is 10000050 T2: restart system. T3: System gives out the next_hi as 10000100 (sequence being dished out now ranges from 101 to 200) T4: Next request for a key returns 100001001 From a primary key or indexing internals perspective, why is it important that there be no gaps in the sequences ? I'm asking this for a deeper understanding of mysql specifically. Thanks

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  • Update n number of records using JPA with Optimistic locking

    - by Jacques René Mesrine
    I have a table with a column called "count" and I want to run a cron job that will trigger a statement that performs a SQL like this: update summaryTable set count=4; Note that there might be concurrent threads reading & changing the value for "count" when this cron job is triggered. The table has a version column to support Optimistic Locking. What's an efficient way to update the count in JPA ?

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  • Dependency on Spring's annotations

    - by Jacques René Mesrine
    I have annotated my classes with @Repository, @Resource, @Component, @Service annotations but these classes must run in 2 environments. The first environment is Spring 2.x based while the other has no spring at all. I'm sure the code will fail without the spring jars & I want to know ideas from you on how I can retain the annotations but still work in both environments

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  • MAD method compression function

    - by Jacques
    I ran across the question below in an old exam. My answers just feels a bit short and inadequate. Any extra ideas I can look into or reasons I have overlooked would be great. Thanx Consider the MAD method compression function, mapping an object with hash code i to element [(3i + 7)mod9027]mod6000 of the 6000-element bucket array. Explain why this is a poor choice of compression function, and how it could be improved. I basically just say that the function could be improved by changing the value for p (or 9027) to an prime number and choosing an other constant for a (or 3) could also help.

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  • Using HTTP Vary header to decide on a strategy to process a request

    - by Jacques René Mesrine
    I have a specific REST endpoint that creates a topic in a forum; but I want to apply different strategies when processing the request. e.g. If client A makes the call, perform moderation. if client B makes the call, do something else. The easiest would be to add a query param for differentiation: POST /resource?from=xyz Another brilliant idea is to use the Vary HTTP header. POST /resource Vary: xyz Any problems with this approach ?

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  • What frameworks to use to bootstrap my first production scala project ?

    - by Jacques René Mesrine
    I am making my first foray into scala for a production app. The app is currently packaged as a war file. My plan is to create a jar file of the scala compiled artifacts and add that into the lib folder for the war file. My enhancement is a mysql-backed app exposed via Jersey & will be integrated with a 3rd party site via HttpClient invocations. I know how to do this via plain java. But when doing it in scala, there are several decision points that I am pussyfooting on. scala 2.7.7 or 2.8 RC ? JDBC via querulous Is this API ready for production ? sbt vs maven. I am comfortable with maven. Is there a scala idiomatic wrapper for HttpClient (or should I use it just like in java) ? I'd love to hear your comments and experiences on starting out with scala. Thanks

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  • Copying a field to another table in Access

    - by Jacques Tardie
    I'm a bit embarassed asking this here, but here goes: I've got two tables, which you can see here: http://img411.imageshack.us/img411/4562/query.jpg I need to copy the effortid from the one table into the other, making sure that the values still maintain the correction relationships. The primary key for each is a combination of loggerid & datetime. What's the best way to do this? Thanks in advance, and don't make fun :)

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  • How do I write JPA QL statements that hints to the runtime to use the DEFAULT value ?

    - by Jacques René Mesrine
    I have a table like so: mysql> show create table foo; CREATE TABLE foo ( network bigint NOT NULL, activeDate datetime NULL default '0000-00-00 00:00:00', ... ) In the domain object, FooVO the activeDate member is annotated as Temporal. If I don't set activeDate to a valid Date instance, a new record is inserted with NULLs. I want the default value to take effect if I don't set the activeDate member. Thanks.

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  • How to differentiate between time to live and time to idle in ehcache

    - by Jacques René Mesrine
    The docs on ehache says: timeToIdleSeconds: Sets the time to idle for an element before it expires. i.e. The maximum amount of time between accesses before an element expires timeToLiveSeconds: Sets the time to live for an element before it expires. i.e. The maximum time between creation time and when an element expires. I understand timeToIdleSeconds But does it means that after the creation & first access of a cache item, the timeToLiveSeconds is not applicable anymore ?

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  • How to turn off autosignin of registered transports in Openfire ?

    - by Jacques René Mesrine
    This is regarding the gateway XEP 0100 support in Openfire. I have noticed that for some transports, they are auto-signed in once a connection to openfire succeeds (via the xmpp user). This applies specifically to QQ. How does one turn off this auto-signin feature ? Basically from a client perspective, I want to be able to signin selectively. So when I create an XMPPConnection to openfire, all transports should remain signed off until I send directed Presences to transports.

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  • scala REPL is slow on vista

    - by Jacques René Mesrine
    I installed scala-2.8.0.RC3 by extracting the tgz file into my cygwin (vista) home directory. I made sure to set $PATH to scala-2.8.0.RC3/bin. I start the REPL by typing: $ scala Welcome to Scala version 2.8.0.RC3 (Java HotSpot(TM) Client VM, Java 1.6.0_20). Type in expressions to have them evaluated. Type :help for more information. scala> Now when I tried to enter an expression scala> 1 + 'a' the cursor hangs there without any response. Granted that I have chrome open with a million tabs and VLC playing in the background, but CPU utilization was 12% and virtual memory was about 75% utilized. What's going on ? Do I have to set the CLASSPATH or perform other steps.

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  • Are there any good sites for blogging about programming?

    - by Jacques Bosch
    I have a few programming articles I would like to write, but I do not have a site of my own - yet ;). Is there a site that is specifically geared toward technical / programming topics, with great functionality and style? Or will I have to go with things like wordpress or blogspot? I would like a site that can track number of views and that has an intuitive commenting system. Any thoughts would be appreciated.

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  • How to ensure that no non-ascii unicode characters are entered ?

    - by Jacques René Mesrine
    Given a java.lang.String instance, I want to verify that it doesn't contain any unicode characters that are not ASCII alphanumerics. e.g. The string should be limited to [A-Za-z0-9.]. What I'm doing now is something very inefficient: import org.apache.commons.lang.CharUtils; String s = ...; char[] ch = s.toCharArray(); for( int i=0; i<ch.length; i++) { if( ! CharUtils.isAsciiAlphanumeric( ch[ i ] ) throw new InvalidInput( ch[i] + " is invalid" ); } Is there a better way to solve this ?

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  • What is the fastest way to learn JPA ?

    - by Jacques René Mesrine
    I'm looking for the best resources (books, frameworks, tutorials) that will help me get up to speed with JPA. I've been happily using iBatis/JDBC for my persistence needs, so I need resources that will hopefully provide comparable functions on how to do things. e.g. how to I set the isolation level for each transaction ? I know there might be 10 books on the topic, so hopefully, your recommendation could narrow down to the best 2 books. Should I start with OpenJPA or are there other opensource JPA frameworks to use ? P.S. Do suggest if I should learn JPA2 or JPA1 ? My goal ultimately is to be able to write a Google App Engine app (which uses JPA1). Thanks Jacque

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  • Partitioning requests in code among several servers

    - by Jacques René Mesrine
    I have several forum servers (what they are is irrelevant) which stores posts from users and I want to be able to partition requests among these servers. I'm currently leaning towards partitioning them by geographic location. To improve the locality of data, users will be separated into regions e.g. North America, South America and so on. Is there any design pattern on how to implement the function that maps the partioning property to the server, so that this piece of code has high availability and would not become a single point of failure ? f( Region ) -> Server IP

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  • All site interaction through a single page

    - by Jacques Wolfghang
    Hi there I have an idea for a site where there would be no refreshing and all interactions take place via AJAX. The page would load with central space, where all interaction would take place. If a user clicked on a link, the page would request it via AJAX and replace the rectangle's content with the link content. The idea is effectively an AJAX implemented iframe. Are there any disadvantages with this approach? Does anyone have any suggestions or thoughts on the idea? Thank You for your time Note: I am sorry if it is not clear or hard to understand, English is not my mother tongue. If there is anything you would like made clearer, please comment and I will try my best to make it understood.

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  • How to maintain a pool of names ?

    - by Jacques René Mesrine
    I need to maintain a list of userids (proxy accounts) which will be dished out to multithreaded clients. Basically the clients will use the userids to perform actions; but for this question, it is not important what these actions are. When a client gets hold of a userid, it is not available to other clients until the action is completed. I'm trying to think of a concurrent data structure to maintain this pool of userids. Any ideas ? Would a ConcurrentQueue do the job ? Clients will dequeue a userid, and add back the userid when they are finished with it.

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  • Convert inline image tags like [image:123:title:size] into HTML img tags

    - by Jacques Joubert
    I am looking for help with regular expression $pattern to convert inline image tags like [image:123:title:size] into HTML img tags. here is the code: //[image:ID:caption:size] $content = '[image:38:title:800x900]'; preg_match_all( '/\[image:(\d+)(:?)([^\]]*)\]/i', $content, $images ); if( !empty( $images[0] ) ) { // There are image inline tags in the content foreach( $images[0] as $i => $tag ) { $link_ID = (int)$images[1][$i]; $caption = empty( $images[2][$i] ) ? '#' : $images[3][$i]; $size = empty( $images[4][$i] ) ? '#' : $images[4][$i]; } echo '<br />'; echo 'ID: '.$link_ID.'<br />'; echo 'Tag: '.$caption.'<br />'; echo 'size: '.$size.'<br />'; } which outputs: ID: 12 Tag: caption:size size: # Any help would be great!

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  • How to find points that intersect an envelope of a line, but not the line itself?

    - by Jacques Bosch
    I have 2 layers. A lines layer and a points layer. For any given line, how can I find the points that intersect the envelope of the line, but not the line itself, or more specifically, not the to point or from point of the line. I can obviously find all the points that intersect the line's envelope, and then do 1 by 1 tests on the found points to see if they intersect the to or from points of the line, but I was hoping there is an easier, faster way to do something of this nature.

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  • Access Validation Rule Violations on Append Query

    - by Jacques Tardie
    I'm recieving the following error on trying to run an append query in access. Microsoft Office Access set .... and it didnt't add... 779280 records(s) due to validation rule violations. If I choose to run the query anyways, nothing actually happens. To give some context, I'm simply trying to copy a populated field, consisting of values similar to "16-2009-02, 34-2010-02, et cetera" to another currently unpopulated field. The fields themselves have no set validation rules, and both have the standard text field options. I'm hoping to be able to simply remove those hyphens, and fix the issue. But I guess that's what I'm not sure about, are those hyphens actually a problem? Running SP3 w/ Access 2003. Thanks in advance!

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