secondary-indexes | 易学教程

What is the definition of secondary index in postgresql?

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问题 From https://www.postgresql.org/docs/9.6/static/indexes-index-only-scans.html: All indexes in PostgreSQL are secondary indexes, meaning that each index is stored separately from the table's main data area (which is called the table's heap in PostgreSQL terminology). In postgresql, is a secondary index defined as an index which is stored separately from the table's main data area? If not, what is its definition, and why does the quote mention the one which is not a definition? Similarly, what

AWS Lambda querying secondary index

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问题 The following is node.js query in AWS lambda on a dynamoDB JSON object. UserID is the primary key with no sort key. GeoHash is a secondary key, with index name "GeoHash-index". The call succeeds with no error, but does not result in anything being returned. It's possible that the test data below is wrong as it does not offer any connection to the index name, but I'm new to AWS/noSQL and a little lost. var AWS = require('aws-sdk'); var docClient = new AWS.DynamoDB({apiVersion: '2012-08-10'});

AWS DynamoDB v2: Do I need secondary index for alternative queries?

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问题 I need to create a table that would contain a slice of data produced by a continuously running process. This process generates messages that contain two mandatory components, among other things: a globally unique message UUID, and a message timestamp. Those messages would be later retrieved by the UUID. In addition, on a regular basis I would need to delete all messages from that table that are too old, i.e. whose timestamps are more than X away from the current time. I've been reading the

Cassandra CQL range query rejected despite equality operator and secondary index

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问题 From the table schema below, I am trying to select all pH readings that are below 5. I have followed these three pieces of advice: Use ALLOW FILTERING Include an equality comparison Create a secondary index on the reading_value column. Here is my query: select * from todmorden_numeric where sensor_name = 'pHradio' and reading_value < 5 allow filtering; Which is rejected with this message: Bad Request: No indexed columns present in by-columns clause with Equal operator I tried adding a

AWS DynamoDB v2: Do I need secondary index for alternative queries?

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I need to create a table that would contain a slice of data produced by a continuously running process. This process generates messages that contain two mandatory components, among other things: a globally unique message UUID, and a message timestamp. Those messages would be later retrieved by the UUID. In addition, on a regular basis I would need to delete all messages from that table that are too old, i.e. whose timestamps are more than X away from the current time. I've been reading the DynamoDB v2 documentation (e.g. Local Secondary Indexes ) trying to figure out how to organize my table

How do I query DynamoDB2 table by global secondary index only using boto 2.25.0?

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问题 This is a continuation** of my quest to switch from regular DynamoDB tables to DynamoDB2 ones with Global Secondary Indices. So I created my table as shown here and then added the following two elements: table.put_item(data={'firstKey': 'key01', 'message': '{"firstKey":"key01", "comments": "mess 1 w/o secondKey"}'}) table.put_item(data={'firstKey': 'key02', 'secondKey':'skey01', 'message': '{"firstKey":"key02", "parentId":"skey01", "comments": "mess 2 w/ secondKey"}'}) What I want to do now

Cassandra CQL range query rejected despite equality operator and secondary index

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From the table schema below, I am trying to select all pH readings that are below 5. I have followed these three pieces of advice: Use ALLOW FILTERING Include an equality comparison Create a secondary index on the reading_value column. Here is my query: select * from todmorden_numeric where sensor_name = 'pHradio' and reading_value < 5 allow filtering; Which is rejected with this message: Bad Request: No indexed columns present in by-columns clause with Equal operator I tried adding a secondary index to the sensor_name column and was told that it was already part of the key and therefore

How do I query DynamoDB2 table by global secondary index only using boto 2.25.0?

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This is a continuation** of my quest to switch from regular DynamoDB tables to DynamoDB2 ones with Global Secondary Indices. So I created my table as shown here and then added the following two elements: table.put_item(data={'firstKey': 'key01', 'message': '{"firstKey":"key01", "comments": "mess 1 w/o secondKey"}'}) table.put_item(data={'firstKey': 'key02', 'secondKey':'skey01', 'message': '{"firstKey":"key02", "parentId":"skey01", "comments": "mess 2 w/ secondKey"}'}) What I want to do now is retrieve items by either their (i) unique firstKey values or (ii) unique secondKey values. The 1st

Validating row at client side better than secondary index with whole primary key?

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问题 In cassandra, it's well known that secondary indexes should be used very sparingly. If I have a table for example: User(username, usertype, email, etc..) Here username is partition key. Now I want to support operation which returns a specific user(username will be given) if and only if usertype is a specific value X. There are two ways I can do it: One: Create a secondary index on usertype, possible values ('A', 'B', 'C') and username is partition key. SELECT * FROM user WHERE username=

Difference between local and global indexes in DynamoDB

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问题 I'm curious about these 2 secondary indexes and differences between them. It is hard to imagine how this looks like. And I think, this will help more people than just me. 回答1: Local Secondary Indexes still rely on the original Hash Key. When you supply a table with hash+range, think about the LSI as hash+range1, hash+range2.. hash+range6. You get 5 more range attributes to query on. Also, there is only one provisioned throughput. Global Secondary Indexes defines a new paradigm - different