indexing

问题 I'm learning MySQL index and found that index should be applied to any column named in the WHERE clause of a SELECT query. Then I found Multiple Column Index vs Multiple Indexes. First Q, I was wondering what is multiple column index. I found code bellow from Joomla, is this Multiple Column Index? CREATE TABLE `extensions` ( `extension_id` INT(11) NOT NULL AUTO_INCREMENT, `name` VARCHAR(100) NOT NULL, `type` VARCHAR(20) NOT NULL, `element` VARCHAR(100) NOT NULL, `folder` VARCHAR(100) NOT NULL

问题 I have a table with the following structure: CREATE TABLE `geo_ip` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `start_ip` int(10) unsigned NOT NULL, `end_ip` int(10) unsigned NOT NULL, PRIMARY KEY (`id`), KEY `start_ip` (`start_ip`), KEY `end_ip` (`end_ip`), KEY `start_end` (`start_ip`,`end_ip`), KEY `end_start` (`end_ip`,`start_ip`)) ENGINE=InnoDB; MySQL seems to be unable to use the indexes for most of my queries, as the where clause uses a between that falls somewhere between start_ip and

问题 I have read that one should not analyze a temp table, as it screws up the table statistics for others. What about an index? If I put an index on the table for the duration of my program, can other programs using the table be affected by that index? Does an index affect my process, and all other processes using the table? or Does it affect my process alone? None of the responses have been authoritative, so I am offering said bribe. 回答1: Does an index effect my process, and all other processes

问题 Sorry about the simple question, but I can't find the proper fix anywhere. I used to have a Rails 3.x app running with a simple landing page on public/index.html. Of course, when I updated to Rails 4, my index page is no longer showing. Is there any way to get that feature back? I know I can create a welcome#index controller/route and render the index.html as a response. But that goes to a different folder, without all the image and css assets that were on public, rendering the former static

问题 I am trying to ensure index on a field of a document and its not working. MongoDB version is 2.0.2. This is very basic and somehow i'm feeling i might have missed something or not!!! Its able to insert 3 docs with same empty string !! Here are details : > use testinsert switched to db testinsert > db.users.ensureIndex({ name : 1}); > doc = { ... name : "" ... } { "name" : "" } > doc { "name" : "" } > db.users.stats(); { "ns" : "testinsert.users", "count" : 0, "size" : 0, "storageSize" : 8192,

问题 In answering another question, I suggested to use timeit to test the difference between indexing a list with positive integers vs. negative integers. Here's the code: import timeit t=timeit.timeit('mylist[99]',setup='mylist=list(range(100))',number=10000000) print (t) t=timeit.timeit('mylist[-1]',setup='mylist=list(range(100))',number=10000000) print (t) I ran this code with python 2.6: $ python2.6 test.py 0.587687015533 0.586369991302 Then I ran it with python 3.2: $ python3.2 test.py 0

问题 Problem To impose np.ndarray periodic boundary conditions as laid out below Details Wrap the indexing of a python np.ndarray around the boundaries in n -dimensions This is a periodic boundary condition forming an n -dimensional torus Wrapping only occurs in the case that the value returned is scalar (a single point). Slices will be treated as normal and will not be wrapped An example and counterexample are given below: a = np.arange(27).reshape(3,3,3) b = Periodic_Lattice(a) # A theoretical

问题 I want to search with Lucene on an index. The index is changed frequently. So I need to do something to search and index at the same time. It's a web application on Tomcat. And I want to use RAMDeirectory to increase the searching speed. I don't know how to do it! 回答1: NRTManager in the misc Lucene package provides the ability to search and index at the same time. TrackingIndexWriter writer; // your writer SearcherFactory factory = new SearcherFactory(); NRTManager mgr = new NRTManager(writer

问题 Given the target ('b', 'a') and the inputs: x0 = ('b', 'a', 'z', 'z') x1 = ('b', 'a', 'z', 'z') x2 = ('z', 'z', 'a', 'a') x3 = ('z', 'b', 'a', 'a') The aim is to find the location of the continuous ('b', 'a') element and get the output: >>> find_ba(x0) 0 >>> find_ba(x1) 0 >>> find_ba(x2) None >>> find_ba(x3) 1 Using the pairwise recipe: from itertools import tee def pairwise(iterable): "s -> (s0,s1), (s1,s2), (s2, s3), ..." a, b = tee(iterable) next(b, None) return zip(a, b) I could do this

问题 I have a large table (star catalog), of which I have a subset. I implement the subset as a union of two tables, where I make use of a cross index. The issue is that a query from the view doesn't seem to be using the index, the time takes the same as a scan through the table. A query against the large table goes quickly: select count(*) from ucac4 where rnm in (select ucac4_rnm from grid_catalog limit 5); count ------- 5 (1 row) Time: 12.132 ms A query against the view does not go quickly,