使用 PATH 对 SQL API 中的数据进行 Azure Cosmos DB 分区和索引

Question

I am collecting IoT data to Azure cosmos DB. I know COSOMOS DB SQL API is auto indexed by Path. I have around 150 sensors in each document, and most of sql queries are of

DeviceId is already Partition Key

Select c.sensorVariable From c where c.DeviceId = 'dev1' AND c.time= date1'

{ "DeviceId" : 'dev1' , "time" : 123333 , "sensor1" : 20 , "sensor2" : 40}

I will Fetch the various sensors data but all my queries are depend on depend on deviceId and time( which is in Unix Timestamp )

Is it possible to index data on deviceID and time and exclude other keys, which are also in the same path / .

And for collection by default

"includedPaths": [
    {
        "path": "/*",
        "indexes": [
            {
                "kind": "Range",
                "dataType": "Number",
                "precision": -1
            },
            {
                "kind": "Range",
                "dataType": "String",
                "precision": -1
            },
            {
                "kind": "Spatial",
                "dataType": "Point"
            }
        ]
    }
],

It comes with this I feel as for DataType String shouldn't it be having Hash kind indexing rather than Range? And what is this Precision : -1

In Azure cosmos DB doc examples I have seen precision as 3 for string, I did not understood why ?

If I have 100 devices and putting data every second level what type of indexing is better ?

Answer 1

Is it possible to index data on deviceID and time and exclude other keys , which are also in the same path

Yes. You could custom your index policy by IncludedPaths and ExcludedPaths .

Such as :

var excluded = new DocumentCollection { Id = "excludedPathCollection" };
excluded.IndexingPolicy.IncludedPaths.Add(new IncludedPath { Path = "/*" });
excluded.IndexingPolicy.ExcludedPaths.Add(new ExcludedPath { Path = "/nonIndexedContent/*" });

await client.CreateDocumentCollectionAsync(UriFactory.CreateDatabaseUri("db"), excluded);

Please refer to more details here .

what is this Precision : -1

In Azure cosmos DB doc examples I have seen precision as 3 for string, I did not understood why ?

Based on Index data types, kinds, and precisions :

For a Hash index, this varies from 1 to 8 for both strings and numbers. The default is 3. For a Range index, this value can be -1 (maximum precision). It can vary from between 1 and 100 (maximum precision) for string or number values.

You could focus on this statement to make your choices.

If i have 100 devices and putting data every second level what type of indexing is better ?

It's hard to say which index mode is the best choice. It should be considered with consistency level and your requirements for read and write performance. You could refer to this paragraph .