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• doublechecking: no db-wide 'unicode switch' for sql server in the foreseeable future, i.e. like Orac

  - by user72150

  Hi all, I believe I know the answer to this question, but wanted to confirm: Question Does Sql server (or will it in the foreseeable future), offer a database-wide "unicode switch" which says "store all characters in unicode (UTF-16, UCS-2, etc)", i.e. like Oracle. The Context Our application has provided "CJK" (Chinese-Japanese-Korean) support for years--using Oracle as the db store. Recently folks have been asking for the same support in sql server. We store our db schema definition in xml and generate the vendor-specific definitions (oracle, sql server) using vendor-specific xsl. We can make the change easily. The problem is for upgrades. Generated scripts would need to change the column types for 100+ columns from varchar to nvarchar, varchar(max) to nvarchar(max), etc. These changes require dropping and recreating indexes and foreign keys if the any indexes/fk's exist on the column. Non-trivial. Risky. DB-wide character encodings for us would eliminate programming changes. (I.e. we would not to change the column types from varchar to nvarchar; sql server would correctly store unicode data in varchar columns). I had thought that eventually sql server would "see the light" and allow storing unicode in varchar/clob columns. Evidently not yet. Recap So just to triple check: does mssql offer a database-wide switch for character encoding? Will it in SQL2008R3? or 2010? thanks, bill

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• Newbie database index question

  - by RenderIn

  I have a table with multiple indexes, several of which duplicate the same columns: Index 1 columns: X, B, C, D Index 2 columns: Y, B, C, D Index 3 columns: Z, B, C, D I'm not very knowledgeable on indexing in practice, so I'm wondering if somebody can explain why X, Y and Z were paired with these same columns. B is an effective date. C is a semi-unique key ID for this table for a specific effective date B. D is a sequence that identifies the priority of this record for the identifier C. Why not just create 6 indexes, one for each X, Y, Z, B, C, D? I want to add an index to another column T, but in some contexts I'll only be querying on T alone while in others I will also be specifying the B, C and D columns... so should I create just one index like above or should I create one for T and one for (T, B, C, D)? I've not had as much luck as expected when googling for comprehensive coverage of indexing. Any resources where I can get a through explanation and lots of examples of B-tree indexing?

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• PostgreSQL - Why are some queries on large datasets so incredibly slow

  - by Brad Mathews

  Hello, I have two types of queries I run often on two large datasets. They run much slower than I would expect them to. The first type is a sequential scan updating all records: Update rcra_sites Set street = regexp_replace(street,'/','','i') rcra_sites has 700,000 records. It takes 22 minutes from pgAdmin! I wrote a vb.net function that loops through each record and sends an update query for each record (yes, 700,000 update queries!) and it runs in less than half the time. Hmmm.... The second type is a simple update with a relation and then a sequential scan: Update rcra_sites as sites Set violations='No' From narcra_monitoring as v Where sites.agencyid=v.agencyid and v.found_violation_flag='N' narcra_monitoring has 1,700,000 records. This takes 8 minutes. The query planner refuses to use my indexes. The query runs much faster if I start with a set enable_seqscan = false;. I would prefer if the query planner would do its job. I have appropriate indexes, I have vacuumed and analyzed. I optimized my shared_buffers and effective_cache_size best I know to use more memory since I have 4GB. My hardware is pretty darn good. I am running v8.4 on Windows 7. Is PostgreSQL just this slow? Or am I still missing something? Thanks! Brad

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• Doing large updates against indexed view

  - by user217136

  We have an indexed view that runs across three large tables. Two of these tables (A & B) are constantly getting updated with user transactions and the other table (C) contains data product info that is needs to be updated once a week. This product table contains over 6 million records. We need this view across these three tables for our core business process and unfortunately we cannot change this aspect. We even had a sql server MVP come in to help test under load to make sure we have the most efficient configuration. There is one column in the product table that gets utilized in the view and has to be updated each week. The problem we are now encountering is that as volume is increasing on our transactions against tables A & B, the update to Table C is causing deadlocks. I have tried several different methods to no avail: 1) I was hoping that we could change the view so that table C could be a dirty read "WITH (NOLOCK)" but apparently that functionality is not available with indexes views. 2) I thought about updating a new column in Table C and then just renaming it when the process is done but you cannot do that due to the dependency in the view. 3) I also entertained the idea of writing this value to a temporary product table, and then running an ALTER statement against the view to have it point to my new table. however when i did that the indexes on my view were dropped and it took quite a bit of time to recreate them. 4) we tried to do the weekly update in small chunks (as small as 100 records at a time) but we still run into dead locks. questions: a) we are using sql server 2005. Does sql server 2008 have a new functionality with their indexed views that would help us? Is there now a way to do dirty reads w/ an indexed view? b) a better approach to altering an existing view to point to a new table? thanks!

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• Jquery CheckBox Selection/Deselection optimally given X checkboxes

  - by Amitd

  Hi guys, I have suppose say 'X' check-boxes(any input elements) in a Form and "M" option selection indexes ("M" less than equal to "X"). then how do i select the "M" option indexes/values and deselect the rest of check-boxes optimally? i.e.Suppose I have 10 Checkboxes and 5 Option Indices(eg: 1,2,4,5,8) then i have to select checkboxes with given index . I could come up with the following code: HTML: <div id="Options"> <input id="choice_1" type="checkbox" name="choice_1" value="Option1"><label for="choice_1">Option1</label> <input id="choice_2" type="checkbox" name="choice_2" value="Option2"><label for="choice_2">Option2</label> <input id="choice_3" type="checkbox" name="choice_3" value="Option3"><label for="choice_3">Option3</label> .. ..till choice_10 </div> IN JS: //Have to select checkboxes with "Value" in choicesToSelect and give a selection //effect to its label var choicesToSelect={"Option1","Option9","Option3","Option4","Option2"}; selectHighlightCheckBoxes(choicesToSelect); function selectHighlightCheckBoxes(choices){ $.each( choices, function(intIndex, objValue) { //select based on id or value or some criteria var option = $("#Options :input[value=" + objValue + "]") ; if ($(option).is("input[type='radio']") || $(option).is("input[type='checkbox']")) { $(option).attr('checked', true); $(option).next('label:first').css({ 'border': '1px solid #FF0000', 'background-color': '#BEF781', 'font-weight': 'bolder' }); } else if ($(option).is("input[type='text']")) { $(option).css({ 'border': '1px solid #FF0000', 'background-color': '#BEF781', 'font-weight': 'bolder' }); } else { } } ); } But i want to also add effect to the rest (not in choicesToSelect array) also. (may be red color to those not in choiceToSelect) Can this be done in the one traversal/loop? Optimally? or Better way?

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• Hadoop Map/Reduce - simple use example to do the following...

  - by alexeypro

  I have MySQL database, where I store the following BLOB (which contains JSON object) and ID (for this JSON object). JSON object contains a lot of different information. Say, "city:Los Angeles" and "state:California". There are about 500k of such records for now, but they are growing. And each JSON object is quite big. My goal is to do searches (real-time) in MySQL database. Say, I want to search for all JSON objects which have "state" to "California" and "city" to "San Francisco". I want to utilize Hadoop for the task. My idea is that there will be "job", which takes chunks of, say, 100 records (rows) from MySQL, verifies them according to the given search criteria, returns those (ID's) which qualify. Pros/cons? I understand that one might think that I should utilize simple SQL power for that, but the thing is that JSON object structure is pretty "heavy", if I put it as SQL schemas, there will be at least 3-5 tables joins, which (I tried, really) creates quite a headache, and building all the right indexes eats RAM faster than I one can think. ;-) And even then, every SQL query has to be analyzed to be utilizing the indexes, otherwise with full scan it literally is a pain. And with such structure we have the only way "up" is just with vertical scaling. But I am not sure it's the best option for me, as I see how JSON objects will grow (the data structure), and I see that the number of them will grow too. :-) Help? Can somebody point me to simple examples of how this can be done? Does it make sense at all? Am I missing something important? Thank you.

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• Help on understanding multiple columns on an index?

  - by Xaisoft

  Assume I have a table called "table" and I have 3 columns, a, b, and c. What does it mean to have a non-clustered index on columns a,b? Is a nonclustered index on columns a,b the same as a nonclustered index on columns b,a? (Note the order). Also, Is a nonclustered index on column a the same as a nonclustered index on a,c? I was looking at the website sqlserver performance and they had these dmv scripts where it would tell you if you had overlapping indexes and I believe it was saying that having an index on a is the same as a,b, so it is redundant. Is this true about indexes? One last question is why is the clustered index put on the primary key. Most of the time the primary key is not queried against, so shouldn't the clustered index be on the most queried column. I am probably missing something here like having it on the primary key speeds up joins? Great explanations. Should I turn this into a wiki and change the title index explanation?

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• automating hudson builds with ant throwing 403

  - by Christopher Dancy

  We have a hudson server which deploys builds. We have a few services which we want to be able to remotely tell hudson to deploy a certain build ... these services are using ant. So I'm trying to get it working but keeping getting a 403 response when giving a build number like so... <ac:post to="http://hostname:8080/hudson/job/test_release_indexes/build?" verbose="true" wantresponse="true"> <prop name="token" value="indexes"/> <prop name="BUILDNUMBER" value="0354"/> </ac:post> this throws the 403. I've also tried passing it props for the username and password like so ... <ac:post to="http://srulesre2:8080/hudson/job/test_dartmouth_indexes/build?" verbose="true" wantresponse="true"> <prop name="token" value="indexes"/> <prop name="BUILDNUMBER" value="0354"/> <prop name="username" value="test"/> <prop name="password" value="test"/> </ac:post> I've tried a hundred different variations on username and password ... like j_username and j_password or user and pass ... but nothing is working ... keep getting the same 403. And the username and password are valid because I can manually log in with admin privileges. Any ideas would be great

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• MySQL FULLTEXT not working

  - by Ross

  I'm attempting to add searching support for my PHP web app using MySQL's FULLTEXT indexes. I created a test table (using the MyISAM type, with a single text field a) and entered some sample data. Now if I'm right the following query should return both those rows: SELECT * FROM test WHERE MATCH(a) AGAINST('databases') However it returns none. I've done a bit of research and I'm doing everything right as far as I can tell - the table is a MyISAM table, the FULLTEXT indexes are set. I've tried running the query from the prompt and from phpMyAdmin, with no luck. Am I missing something crucial? UPDATE: Ok, while Cody's solution worked in my test case it doesn't seem to work on my actual table: CREATE TABLE IF NOT EXISTS `uploads` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` text NOT NULL, `size` int(11) NOT NULL, `type` text NOT NULL, `alias` text NOT NULL, `md5sum` text NOT NULL, `uploaded` datetime NOT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=6 ; And the data I'm using: INSERT INTO `uploads` (`id`, `name`, `size`, `type`, `alias`, `md5sum`, `uploaded`) VALUES (1, '04 Sickman.mp3', 5261182, 'audio/mp3', '1', 'df2eb6a360fbfa8e0c9893aadc2289de', '2009-07-14 16:08:02'), (2, '07 Dirt.mp3', 5056435, 'audio/mp3', '2', 'edcb873a75c94b5d0368681e4bd9ca41', '2009-07-14 16:08:08'), (3, 'header_bg2.png', 16765, 'image/png', '3', '5bc5cb5c45c7fa329dc881a8476a2af6', '2009-07-14 16:08:30'), (4, 'page_top_right2.png', 5299, 'image/png', '4', '53ea39f826b7c7aeba11060c0d8f4e81', '2009-07-14 16:08:37'), (5, 'todo.txt', 392, 'text/plain', '5', '7ee46db77d1b98b145c9a95444d8dc67', '2009-07-14 16:08:46'); The query I'm now running is: SELECT * FROM `uploads` WHERE MATCH(name) AGAINST ('header' IN BOOLEAN MODE) Which should return row 3, header_bg2.png. Instead I get another empty result set. My options for boolean searching are below: mysql> show variables like 'ft_%'; +--------------------------+----------------+ | Variable_name | Value | +--------------------------+----------------+ | ft_boolean_syntax | + -><()~*:""&| | | ft_max_word_len | 84 | | ft_min_word_len | 4 | | ft_query_expansion_limit | 20 | | ft_stopword_file | (built-in) | +--------------------------+----------------+ 5 rows in set (0.02 sec) "header" is within the word length restrictions and I doubt it's a stop word (I'm not sure how to get the list). Any ideas?

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• Web page database query optimization

  - by morpheous

  I am putting together a web page which is quite 'expensive' in terms of database hits. I don't want to start optimizing at this stage - though with me trying to hit a deadline, I may end up not optimizing at all. Currently the page requires 18 (that's right eighteen) hits to the db. I am already using joins, and some of the queries are UNIONed to minimize the trips to the db. My local dev machine can handle this (page is not slow) however, I feel if I release this into the wild, the number of queries will quickly overwhelm my database (MySQL). I could always use memcache or something similar, but I would much rather continue with my other dev work that needs to be completed before the deadline - at least retrieving the page works - its simply a matter of optimization now (if required). My question therefore is - is 18 db queries for a single page retrieval completely outrageous - (i.e. I should put everything on hold and optimize the hell of the retrieval logic), or shall I continue as normal, meet the deadline and release on schedule and see what happens? [Edit] Just to clarify, I have already done the 'obvious' things like using (single and composite) indexes for fields used in the queries. What I haven't yet done is to run a query analyzer to see if my indexes etc are optimal.

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• Rewrite to support folders as domain aliases while hiding subfolders

  - by user1692328

  I am trying to use domain aliases to point to subfolders on my site where the subfolders name would be hidden from resulting url on rewrite. domain-alias1.com and domain-alias2.com are domain aliases to domain.com I have the following in my root: domain.com/ .htaccess (listed below) domain-alias1/ main/ .htaccess (contains only Options -Indexes) domain-alias2/ ... /.htaccess follows: RewriteEngine on RewriteBase / RewriteCond %{HTTP_HOST} ^domain-alias1\.com$ [NC,OR] RewriteCond %{HTTP_HOST} ^www\.domain-alias1\.com$ [NC] RewriteCond %{REQUEST_URI} !^/domain-alias1 RewriteRule ^(.*)$ domain-alias1/$1 [L] RewriteCond %{HTTP_HOST} ^domain-alias2\.com$ [NC,OR] RewriteCond %{HTTP_HOST} ^www\.domain-alias2\.com$ [NC] RewriteCond %{REQUEST_URI} !^/domain-alias2 RewriteRule ^(.*)$ domain-alias2/$1 [L] domain-alias1.com (yields) - Forbidden. You don't have permission to access /cogeco-gis/ on this server. (Which is what I want since .htaccess in domain.com/domain-alias1 contains Options -Indexes) domain-alias1.com/test (yields) - Not Found. The requested URL /domain-alias1/test was not found on this server. (Which is what I expect since test does not exist) domain-alias1.com/main (yields) - domain-alias1.com/domain-alias1/main/login_page.php I am expecting rewrite to yield : domain-alias1.com/main/login_page.php where subfolder domain-alias1 is hidden from resulting url) Any help on how to get expected results?

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• Reversing permutation of an array in Java efficiently

  - by HansDampf

  Okay, here is my problem: Im implementing an algorithm in Java and part of it will be following: The Question is to how to do what I will explain now in an efficient way. given: array a of length n integer array perm, which is a permutation of [1..n] now I want to shuffle the array a, using the order determined by array perm, i.e. a=[a,b,c,d], perm=[2,3,4,1] ------ shuffledA[b,c,d,a], I figured out I can do that by iterating over the array with: shuffledA[i]=a[perm[i-1]], (-1 because the permutation indexes in perm start with 1 not 0) Now I want to do some operations on shuffledA... And now I want to do the reverse the shuffle operation. This is where I am not sure how to do it. Note that a can hold an item more than once, i.e. a=[a,a,a,a] If that was not the case, I could iterate perm, and find the corresponding indexes to the values. Now I thought that using a Hashmap instead of the the perm array will help. But I am not sure if this is the best way to do.

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• SQL Server 2008 spatial index and CPU utilization with MapGuide Open Source 2.1

  - by Antonio de la Peña

  I have a SQL Server table with hundreds of thousands of geometry type parcels. I have made indexes on them trying different combinations of density and objects per cell settings. So far I'm settiling for LOW, LOW, MEDIUM, MEDIUM and 16 objects per cell and I made a SP that sets the bounding box according to the extents of the entities in the table. There is an incredible performance boost from queries taking almost minutes without index to less than seconds, it gets faster when the zoom is closer thus less objects are displayed. Yet the CPU utilization gets to 100% when querying for features, even when the queries themselves are fast. I'm worrying this will not fly in a production environment. I am using MapGuide Open Source 2.1 for this project, but I am positive the CPU load is caused by SQL Server. I wonder if my indexes are set properly. I haven't found any clear documentation on how to properly set them up. Every article I've read basically says "it depends..." but nothing specific. Do you have any recommendations for me, including books, articles? Thank you.

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• how to model a follower stream in appengine?

  - by molicule

  I am trying to design tables to buildout a follower relationship. Say I have a stream of 140char records that have user, hashtag and other text. Users follow other users, and can also follow hashtags. I am outlining the way I've designed this below, but there are two limitaions in my design. I was wondering if others had smarter ways to accomplish the same goal. The issues with this are The list of followers is copied in for each record If a new follower is added or one removed, 'all' the records have to be updated. The code class HashtagFollowers(db.Model): """ This table contains the followers for each hashtag """ hashtag = db.StringProperty() followers = db.StringListProperty() class UserFollowers(db.Model): """ This table contains the followers for each user """ username = db.StringProperty() followers = db.StringListProperty() class stream(db.Model): """ This table contains the data stream """ username = db.StringProperty() hashtag = db.StringProperty() text = db.TextProperty() def save(self): """ On each save all the followers for each hashtag and user are added into a another table with this record as the parent """ super(stream, self).save() hfs = HashtagFollowers.all().filter("hashtag =", self.hashtag).fetch(10) for hf in hfs: sh = streamHashtags(parent=self, followers=hf.followers) sh.save() ufs = UserFollowers.all().filter("username =", self.username).fetch(10) for uf in ufs: uh = streamUsers(parent=self, followers=uf.followers) uh.save() class streamHashtags(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() class streamUsers(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() Now, to get the stream of followed hastags indexes = db.GqlQuery("""SELECT __key__ from streamHashtags where followers = 'myusername'""") keys = [k,parent() for k in indexes[offset:numresults]] return db.get(keys) Is there a smarter way to do this?

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• wordpress generating slow mysql queries - is it index problem?

  - by tash

  Hello Stack Overflow I've got very slow Mysql queries coming up from my wordpress site. It's making everything slow and I think this is eating up CPU usage. I've pasted the Explain results for the two most frequently problematic queries below. This is a typical result - although very occasionally teh queries do seem to be performed at a more normal speed. I have the usual wordpress indexes on the database tables. You will see that one of the queries is generated from wordpress core code, and not from anything specific - like the theme - for my site. I have a vague feeling that the database is not always using the indexes/is not using them properly... Is this right? Does anyone know how to fix it? Or is it a different problem entirely? Many thanks in advance for any help anyone can offer - it is hugely appreciated Query: [wp-blog-header.php(14): wp()] SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') ORDER BY wp_posts.post_date DESC LIMIT 0, 6 id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE wp_posts ref type_status_date type_status_date 63 const 427 Using where; Using filesort Query time: 34.2829 (ms) 9) Query: [wp-content/themes/LMHR/index.php(40): query_posts()] SELECT SQL_CALC_FOUND_ROWS wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.ID NOT IN ( SELECT tr.object_id FROM wp_term_relationships AS tr INNER JOIN wp_term_taxonomy AS tt ON tr.term_taxonomy_id = tt.term_taxonomy_id WHERE tt.taxonomy = 'category' AND tt.term_id IN ('217', '218', '223', '224') ) AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') ORDER BY wp_posts.post_date DESC LIMIT 0, 6 id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY wp_posts ref type_status_date type_status_date 63 const 427 Using where; Using filesort 2 DEPENDENT SUBQUERY tr ref PRIMARY,term_taxonomy_id PRIMARY 8 func 1 Using index 2 DEPENDENT SUBQUERY tt eq_ref PRIMARY,term_id_taxonomy,taxonomy PRIMARY 8 antin1_lovemusic2010.tr.term_taxonomy_id 1 Using where Query time: 70.3900 (ms)

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• New record may be written twice in clusterd index structure

  - by Cupidvogel

  As per the article at Microsoft, under the Test 1: INSERT Performance section, it is written that For the table with the clustered index, only a single write operation is required since the leaf nodes of the clustered index are data pages (as explained in the section Clustered Indexes and Heaps), whereas for the table with the nonclustered index, two write operations are required—one for the entry into the index B-tree and another for the insert of the data itself. I don't think that is necessarily true. Clustered Indexes are implemented through B+ tree structures, right? If you look at at this article, which gives a simple example of inserting into a B+ tree, we can see that when 8 is initially inserted, it is written only once, but then when 5 comes in, it is written to the root node as well (thus written twice, albeit not initially at the time of insertion). Also when 8 comes in next, it is written twice, once at the root and then at the leaf. So won't it be correct to say, that the number of rewrites in case of a clustered index is much less compared to a NIC structure (where it must occur every time), instead of saying that rewrite doesn't occur in CI at all?

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• Avoid an "out of memory error" in Java(eclipse), when using large data structure?

  - by gnomed

  OK, so I am writing a program that unfortunately needs to use a huge data structure to complete its work, but it is failing with a "out of memory error" during its initialization. While I understand entirely what that means and why it is a problem, I am having trouble overcoming it, since my program needs to use this large structure and I don't know any other way to store it. The program first indexes a large corpus of text files that I provide. This works fine. Then it uses this index to initialize a large 2D array. This array will have nXn entries, where "n" is the number of unique words in the corpus of text. For the relatively small chunk I am testing it on(about 60 files) it needs to make approximately 30,000x30,000 entries. this will probably be bigger once I run it on my full intended corpus too. It consistently fails every time, after it indexes, while it is initializing the data structure(to be worked on later). Things I have done include: revamp my code to use a primitive "int[]" instead of a "TreeMap" eliminate redundant structures, etc... Also, I have run eclipse with "eclipse -vmargs -Xmx2g" to max out my allocated memory I am fairly confident this is not going to be a simple line of code solution, but is most likely going to require a very new approach. I am looking for what that approach is, any ideas? Thanks, B.

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• Mysql random rows

  - by n00b

  please read the whole question... 90% of you dont seem to do that and some of you only read the title obviously... and if you dont know the solution, dont answer - i wont have to downvote you -.-'' im entertaining the idea of getting random rows directly from mysql. what i found was SELECT * FROM tablename WHERE somefield='something' ORDER BY RAND() LIMIT 5 but even i see how slow that would be.. is the only way to do this doing something like SELECT * FROM tablename WHERE somefield='something' LIMIT RAND(aincrementvalue-5), 1 5 times? or is there a way that i with my little knowlege of databases cant come up with ? (no i dont want random indexes. i hate the idea of them...) @commenters - please first look, then think, then look again, think again and then post. i wont point fingers but i dislike stupid comments and why i think random indexes are a nasty hack ? it doesnt give you random results. it gives you x results from a random index in a predefined order its like a gapless id only in the wrong order if you fetch by 1 row and get true randomness you fall back to my method but with an additional junk field finally the reason the field exists is only to serve as a helper to something that can be done without it with almost same performance (but the quality (randomness) is better), so it is a nasty hack ;) i solved it, look @ my answer... if you think its incorrect please tell me :)

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• Subset and lagging list data structure R

  - by user1234440

  I have a list that is indexed like the following: >list.stuff [[1]] [[1]]$vector ... [[1]]$matrix .... [[1]]$vector [[2]] null [[3]] [[3]]$vector ... [[3]]$matrix .... [[3]]$vector . . . Each segment in the list is indexed according to another vector of indexes: >index.list 1, 3, 5, 10, 15 In list.stuff, only at each of the indexes 1,3,5,10,15 will there be 2 vectors and one matrix; everything else will be null like [[2]]. What I want to do is to lag like the lag.xts function so that whatever is stored in [[1]] will be pushed to [[3]] and the last one drops off. This also requires subsetting the list, if its possible. I was wondering if there exists some functions that handle list manipulation. My thinking is that for xts, a time series can be extracted based on an index you supply: xts.object[index,] #returns the rows 1,3,5,10,15 From here I can lag it with: lag.xts(xts.object[index,]) Any help would be appreciated thanks: EDIT: Here is a reproducible example: list.stuff<-list() vec<-c(1,2,3,4,5,6,7,8,9) vec2<-c(1,2,3,4,5,6,7,8,9) mat<-matrix(c(1,2,3,4,5,6,7,8),4,2) list.vec.mat<-list(vec=vec,mat=mat,vec2=vec2) ind<-c(2,4,6,8,10) for(i in ind){ list.stuff[[i]]<-list.vec.mat }

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• Best way to migrate export/import from SQL Server to oracle

  - by matao

  Hi guys! I'm faced with needing access for reporting to some data that lives in Oracle and other data that lives in a SQL Server 2000 database. For various reasons these live on different sides of a firewall. Now we're looking at doing an export/import from sql server to oracle and I'd like some advice on the best way to go about it... The procedure will need to be fully automated and run nightly, so that excludes using the SQL developer tools. I also can't make a live link between databases from our (oracle) side as the firewall is in the way. The data needs to be transformed in the process from a star schema to a de-normalised table ready for reporting. What I'm thinking about is writing a monster query for SQL Server (which I mostly have already) that will denormalise and read out the data from SQL Server into a flat file using the sql server equivalent of sqlplus as a scheduled task, dump into a Well Known Location, then on the oracle side have a cron job that copies down the file and loads it with sql loader and rebuilds indexes etc. This is all doable, but very manual. Is there one or a combination of FOSS or standard oracle/SQL Server tools that could automate this for me? the Irreducible complexity is the query on one side and building indexes on the other, but I would love to not have to write the CSV dumping detail or the SQL loader script, just say dump this view out to CSV on one side, and on the other truncate and insert into this table from CSV and not worry about mapping column names and all other arcane sqlldr voodoo... best practices? thoughts? comments? edit: I have about 50+ columns all of varying types and lengths in my dataset, which is why I'd prefer to not have to write out how to generate and map each single column...

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• How lucene indexing ?

  - by user312140

  Hello I read some document about lucene ; also i read the document in this link ( http://lucene.sourceforge.net/talks/pisa ) . I don't really understand how lucene index documents and don't understand lucene work with which algorithm for indexing ? On above link , said lucene use this algorithm for indexing : * incremental algorithm: o maintain a stack of segment indices o create index for each incoming document o push new indexes onto the stack o let b=10 be the merge factor; M=8 for (size = 1; size < M; size *= b) { if (there are b indexes with size docs on top of the stack) { pop them off the stack; merge them into a single index; push the merged index onto the stack; } else { break; } } How this algorithm help us to have an optimize indexing ? Does lucene use B-tree algorithm or any other algorithm like that for indexing or have a paticular algorithm ? Thank you for reading my post .

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• Java convert time format to integer or long

  - by behrk2

  Hello, I'm wondering what the best method is to convert a time string in the format of 00:00:00 to an integer or a long? My ultimate goal is to be able to convert a bunch of string times to integers/longs, add them to an array, and find the most recent time in the array... I'd appreciate any help, thanks! Ok, based on the answers, I have decided to go ahead and compare the strings directly. However, I am having some trouble. It is possible to have more than one "most recent" time, that is, if two times are equal. If that is the case, I want to add the index of both of those times to an ArrayList. Here is my current code: days[0] = "15:00:00"; days[1] = "17:00:00"; days[2] = "18:00:00"; days[3] = "19:00:00"; days[4] = "19:00:00"; days[5] = "15:00:00"; days[6] = "13:00:00"; ArrayList<Integer> indexes = new ArrayList<Integer>(); String curMax = days[0]; for (int x = 1; x < days.length1; x++) { if (days[x].compareTo(curMax) > 0) { curMax = days[x]; indexes.add(x); System.out.println("INDEX OF THE LARGEST VALUE: " + x); } } However, this is adding index 1, 2, and 3 to the ArrayList... Can anyone help me?

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• problem with a very simple tile based game

  - by newbieguy

  Hello, I am trying to create a pacman-like game. I have an array that looks like this: array: 1111111111111 1000000000001 1111110111111 1000000000001 1111111111111 1 = Wall, 0 = Empty space I use this array to draw tiles that are 16x16 in size. The Game character is 32x32. Initially I represented the character's position in array indexes, [1,1] etc. I would update his position if array[character.new_y][charater.new_x] == 0 Then I translated these array coordinates to pixels, [y*16, x*16] to draw him. He was lining up nicely, wouldn't go into walls, but I noticed that since I was updating him by 16 pixels each, he was moving very fast. I decided to do it in reverse, to store the game character's position in pixels instead, so that he could use less than 16 pixels per move. I thought that a simple if statement such as this: if array[(character.new_pixel_y)/16][(character.new_pixel_x)/16] == 0 would prevent him from going into walls, but unfortunately he eats a bit of the bottom and right side walls. Any ideas how would I properly translate pixel position to the array indexes? I guess this is something simple, but I really can't figure it out :(

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• Array's index and argc signedness

  - by tusbar

  Hello, The C standard (5.1.2.2.1 Program startup) says: The function called at program startup is named main. [...] It shall be de?ned with a return type of int and with no parameters: int main(void) { /* ... */ } or with two parameters [...] : int main(int argc, char *argv[]) { /* ... */ } And later says: The value of argc shall be nonnegative. Why shouldn't argc be defined as an unsigned int, argc supposedly meaning 'argument count'? Should argc be used as an index for argv? So I started wondering if the C standard says something about the type of array's index. Is it signed? 6.5.2.1 Array subscripting: One of the expressions shall have type ‘‘pointer to object type’’, the other expression shall have integer type, and the result has type ‘‘type’’. It doesn't say anything about its signedness (or I didn't find it). It is pretty common to see codes using negatives array indexes (array[-1]) but isn't it undefined behavior? Should array's indexes be unsigned?

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• How to speed-up a simple method (preferably without changing interfaces or data structures)?

  - by baol

  I have some data structures: all_unordered_m is a big vector containing all the strings I need (all different) ordered_m is a small vector containing the indexes of a subset of the strings (all different) in the former vector position_m maps the indexes of objects from the first vector to their position in the second one. The string_after(index, reverse) method returns the string referenced by ordered_m after all_unordered_m[index]. ordered_m is considered circular, and is explored in natural or reverse order depending on the second parameter. The code is something like the following: struct ordered_subset { // [...] std::vector<std::string>& all_unordered_m; // size = n >> 1 std::vector<size_t> ordered_m; // size << n std::tr1::unordered_map<size_t, size_t> position_m; const std::string& string_after(size_t index, bool reverse) const { size_t pos = position_m.find(index)->second; if(reverse) pos = (pos == 0 ? orderd_m.size() - 1 : pos - 1); else pos = (pos == ordered.size() - 1 ? 0 : pos + 1); return all_unordered_m[ordered_m[pos]]; } }; Given that: I do need all of the data-structures for other purposes; I cannot change them because I need to access the strings: by their id in the all_unordered_m; by their index inside the various ordered_m; I need to know the position of a string (identified by it's position in the first vector) inside ordered_m vector; I cannot change the string_after interface without changing most of the program. How can I speed up the string_after method that is called billions of times and is eating up about 10% of the execution time?

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