nosql

问题 I've been toying around with Map Reduce with CouchDB. Some of the examples show some possibly heavy logic within the map reduce functions. In one particular case, they were performing for loops within map. Is map reduce run on every single possible document before it emits your selected documents? If so, I would think that means that running any kind of iterative processing within the map reduce functions would increase processing burden by an order of magnitude, at least. Basically it boils

问题 What is the best way to check if table exists in DynamoDb? I would appreciate it if the code would be in PHP. Either active or not. * Added later as an example to various cases for error code 400 It's very easy to check if the table exist, it can have one of the following TableStatus => CREATING, ACTIVE, DELETING or UPDATING but in case i get error 400 it can mean more than one thing. 1) sent null string as a table name by mistake. [x-aws-body] => {"TableName":""} ) [body] => CFSimpleXML

问题 What is the meaning of eventual consistency in Cassandra when nodes in a single cluster do not contain the copies of same data but data is distributed among nodes. Now since a single peice of data is recorded at a single place (node). Why wouldn't Cassandra return the recent value from that single place of record? How do multiple copies arise in this situation? 回答1: Its up to the client to decide the appropriate consistency level (zero, any, one, quoram or all). (The consistency level

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 5 years ago . I'm looking for an API with the following requirements It's simple to use and is concise. It is not bloated. Works with Spring way of doing things, or is at least easy to make it work with Spring Has a Maven repository, preferably it's already in the main repositories Is production-tested, meaning a fair number

问题 I have used mongodb database and node.js v12.0.10 for connecting and updating mongodb collection. connection code is the following: async.parallel({ RE5: function (cb) { MongoClient.connect(config.riskEngineDB, function (err, r5DB) { cb(err, r5DB); }) }, MDB: function (cb) { MongoClient.connect(config.monitoringDB, function (err, mDB) { cb(err, mDB); }) } }, function (err, DBs) { assert.equal(null, err); console.log("Connected correctly to Dbs"); // ..doing updates.. }) after some time

问题 I'm weighing up having separate DBs (one per company) vs one multi-tenanted DB (with all companies). Criteria: A user can belong to one company only and can't access documents of other companies. An administrator of the system needs to maintain DBs for all firms. Number of companies/tenants - from hundreds to tens of thousands There is one entry point with authentication, for all companies/tenants (it'll resolve the tenant and address it to the right DB). Question #1 . Are there any "good

问题 I read this question Many to Many relationship in Firebase, and here describes how to create or structure many to many relationship within firebase(nosql database), and it is pretty easy, companyContractors companyKey1 contractorKey1: true contractorKey3: true companyKey2 contractorKey2: true contractorCompanies contractorKey1 companyKey1: true, companyKey2: true contractorKey2 companyKey2: true contractorKey3 companyKey1: true but when i want to get all contractors specific company, can i do

问题 I'm looking for one place that summarizes the main properties of the NoSQL databases that I keep seeing referenced - in particular, MongoDB, Riak, Redis, Memcached, Membase, and Cassandra. Types of queries, acid, architecture for/properties of scaling, etc. All in memory, overflow to disk, backup on disk, or mainly only indexes in memory? 回答1: Probably one of the best source which summarizes basic information (and points you to more detailed source in the first place) about various nosql

问题 I'm trying to grasp how Azure table storage works to create facebook-style feeds and I'm stuck on how to retrieve the entries. (My questions is almost the same as https://stackoverflow.com/questions/6843689/retrieve-multiple-type-of-entities-from-azure-table-storage but the link in the answer is broken.) This is my intended approach: Create a personal feed for all users within my application which can contain different types of entries (notification, status update etc). My idea is to store

问题 My mental model was that of a 'chat', where I am subscribed to a certain channel and I can publish messages to this channel. 回答1: Since pub/sub is asynchronous, the published message could appear at any time, including when you are expecting the response to a command. Although redis is single threaded, which normally prevents that sort of thing, network latency can cause some interesting effects - depending on the content of the messages, you could receive a valid response to a command before