indexing

问题 I have an existing index build using apache solr 1.4. I want to use this existing index in version 3.3. As you know the index format is changed after 3.x, so how is it possible to do this? I have exported the existing index (that is in 1.4 version) using Luke to XML. 回答1: There's two ways to do this: if your index is unoptimized, then simply optimize it - this will upgrade the file format along the way. if your index is already optimized, you can't do this. Instead, use the command line tool

问题 I have a metric table that I expect to be very large. It has a polymorphic association so that it can belongs_to other models that want to record some metric. I typically index association columns like this to speed up association loading. I've heard people talking about joint-indexing this association. This looks like: add_index :comments, [:commentable_type, :commentable_id] But I've also heard counsel against creating indexes of low-cardinality, because the payoff of the index doesn't

问题 I'm trying to create an index on the cast of a varchar column to date. I'm doing something like this: CREATE INDEX date_index ON table_name (CAST(varchar_column AS DATE)); I'm getting the error: functions in index expression must be marked IMMUTABLE But I don't get why, the cast to date doesn't depends on the timezone or something like that (which makes a cast to timestamp with time zone give this error). Any help? 回答1: Your first error was to store a date as a varchar column. You should not

问题 I want to use values from a dictionary in my UITableViewCells. Can I get those from a dictionary by using indexPath.row for the value and indexPath.section for the key? 回答1: you can get the keys array and get the key at indexPath.section like this: Array(yourDictionary.keys)[indexPath.section] and you can get the value at indexPath.row from the values array like this: Array(yourDictionary.values)[indexPath.row] Edit: if you want to get the values of a specific section key you should write:

问题 Is creating an index for a column that is being summed is faster than no index? 回答1: Sorry, it is not clear what you are asking. Are you asking, would it speed up a query such as SELECT product, sum(quantity) FROM receipts GROUP BY product if you added an index on quantity? If that is the question, then the answer is no. Generally speaking, indexes are helpful when you need to find just a few rows among many; here you need all rows, so an index does not help. There is an obscure exception

问题 I would like to call ensureIndex on the authorName , what is the command and where in this code should I put it? var mongoose = require('mongoose'); // defines the database schema for this object var schema = mongoose.Schema({ projectName : String, authorName : String, comment : [{ id : String, authorName : String, authorEmailAddress : { type : String, index : true } }] }); // Sets the schema for model var ProjectModel = mongoose.model('Project', schema); // Create a project exports.create =

问题 Are there any open source or commercial tools available that allow for text fragment indexing of database contents and can be queried from Java? Background of the question is a large MySQL database table with several hundred thousand records, containing several VARCHAR columns. In these columns people would like to search for fragments of the contents, so a fulltext index (which is based on word boundaries) would not help. EDIT : [Added to make clear why these first suggestions would not

问题 Been working with MongoDB for a while and today I had a doubt while discussing with a colleague. The thing is that when you create an index in MongoDB, the collection is processed and the index is built. The index is updated within insertion and deletion of documents so I don't really see the need to run a rebuild index operation (which drops the index and then rebuild it). According to MongoDB documentation: Normally, MongoDB compacts indexes during routine updates. For most users, the

问题 I have this code: <div class="row list-group"> <div *ngFor="let product of products" > <app-product [product]="product"></app-product> </div> </div> I was wondering is there any way i can get products from array in buckets? Something like this: <div class="list-group"> <div *ngFor="products; index+3" > <div class="row"> <app-product [product]="products[index]"></app-product> <app-product [product]="products[index+1]"></app-product> <app-product [product]="products[index+2]"></app-product> <

问题 I would like to monitor index usage for an sql database, in order to find unused indexes and then drop them. How can I monitor index usage most efficiently? And which scripts could be useful? (I'm aware of this question about identifying unused objects, but this applies only to the current run of the sql server. I would like to monitor index usage over a period of time...) 回答1: Currently (as of SQL Server 2005 - 2008) the SQL index stats information is only kept in memory and so you have to