indexing

问题 I would like to know a few things regarding mysql architecture. 1. How sql process insert, delete, update operations in an indexed table? 2. It is said that changes are only made in the change buffer when the index page is not in the buffer pool. So if changes are made after the buffer pool loads the concerned index page, then it has to alter the same page in disk as well. right? So an operation has to be done in three different places? 3. How NULL values are indexed? where would they be

问题 Given this query, which column or columns should be indexed to optimize query performance? SELECT * FROM `activities` WHERE (user_id = 90000 AND activity_type_id IN(300,400,808,9494)) ORDER BY created_at DESC LIMIT 70 回答1: In general, the selection filters can use indexes on user_id or activity_type_id or both (in either order). The ordering operation might be able to use a filter on created_at . It is likely that for this query, a composite index on (user_id, activity_type_id) would give the

问题 I have an entity framework query that has this at the heart of it: SELECT 1 AS dummy FROM [dbo].[WidgetOrder] AS widgets WHERE widgets.[SomeOtherOrderId] = N'SOME VALUE HERE' The execution plan for this chooses an index that is a composite of three columns. This takes 10 to 12 seconds. However, there is an index that is just [SomeOtherOrderId] with a few other columns in the "include". That is the index that should be used. And when I run the following queries it is used: SELECT 1 AS dummy

问题 I have a website I've designed for a client here: http://www.haniabyanyacole.com I'm using a meta http-equiv="refresh" to redirect the user from the splash page to haniabyanyacole.com/site/ (I know that's not recommended) and I think this is causing Google to return the first search result for the company's name with http://haniabyanyacole.com/site instead of the root directory. Is there a redirect solution (301, 302?) that will force Google to index the root instead of /site/? FYI I have

问题 Trying to retrieve the index of sorted list "second". "second" contains same values as "first" and will be reordered to become identical order as "first". I'm looking for an indexlist "d" which contains the the reordered indexes from old "second". tryied to retrieve "d" with zip or enumerate, but failed. first= [(11.373,0.354,6.154),(22.354,0.656,0.664),(33.654,33.546,31.131)] second=[(22.354,0.656,0.664),(33.654,33.546,31.131),(11.373,0.354,6.154)] second=sorted(second,key=first.index) print

问题 When we make a git diff Version1..Version2 -- file , this command will return something like : diff --git a/wp-includes/version.php b/wp-includes/version.php index 5d034bb9d8..617021e8d9 100644 The git here compare between two version of a file to give you the difference between them. I need to know the commit responsible for adding the file in question from the number of index 5d034bb9d8 , and the index **617021e8d9*. 回答1: TL;DR This (untested) script may do what you want. Read the rest for

问题 By default, documentdb creates an index on every path in a JSON. If we insert a JSON with twenty key-value pairs, documentdb will create indexes on all of these values. Whereas in SQL server, having twenty indexes on a general table is not desirable (especially on transaction tables). So why documentdb does this? Is it because it works on most of the scenarios in documentdb? If So, why? 回答1: Because DocumentDB is designed for schema and query flexibility. DocumentDB is a NoSQL database that

问题 Should I be careful adding too many include columns to a non-cluster index? I understand that this will prevent bookmark look-ups on fully covered queries, but the counter I assume is there's the additional cost of maintaining the index if the columns aren't static and the additional overall size of the index causing additional physical reads. 回答1: You said it in the question: the risk with having many indexes and/or many columns in indexes is that the cost of maintaining the indexes may

问题 I have a project (big project), that takes about 30 minutes to be indexed by Xcode. Xcode consumes 100% of my CPU for 30mn. OK why not, that sounds a bit rude to use 100% of the CPU for a background task, but why not. Now, if after 30 minutes, I quit Xcode, and re-open it, without touching a single file of my project, it starts again to index for 30 minutes. Is this the intended behaviour? Is there a way to fix it? I don't want to turn off inedxing, I tried it, and code completion is HS. 回答1:

问题 I have 3 series which is generated out of the code shown below. I have shown a the code for one series below I would like to merge 3 such series/dataframes using columns (subject_id,hadm_id,icustay_id) but unfortunately these headings don't appear as column names. How do I convert them as columns and use them for merging with another series/dataframe of similar datatype I am generating series from another dataframe (df) based on the condition given below. Though I already tried converting