Learn on AWS DynamoDB

Basic Concept

  • Tables: same with RDS
  • Items: similar as record/row in RDS
  • Attributes: similarcolumns in RDS

Feature

  • A key-value and document database
  • Fully cloud host, auto scale
  • No connection pool, only concurrent concept to avoid break limit for Dynamodb API is based on web service.

Structure

  • Table: A table is a collection of data
  • Item: Similar to row in RDB, Each table contains zero or more items. An item is a group of attributes that is uniquely identifiable among all of the other items.
  • Attribute: Each item is composed of one or more attributes. An attribute is a fundamental data element. Similar to column in RDB, each item contains multiple attributes.

Keys

  • Primary key (aka: Primary Index)
  • Secondary Index
    • Local Secondary Indexes (LSI)
    • Global Secondary Indexe (GSI)

Primary key

Table must define the primary key, support two types:

  • partition key:
    • aka: hash attribute
    • should be unique
    • dynamo will run hash function on this to decide partition for physical storage.
  • partition key and sort key:
    • a composite key with two attributes
    • aka: hash attribute + range attribute
    • partition key + sort key should be unique, while partition key can be not unique.
    • All items with the same partition key value are stored together, in sorted order by sort key.

More introduction:

  • The only data types allowed for primary key attributes are string, number, or binary

Secondary Index

DynamoDB supports two kinds of indexes:

  • Global secondary index – An index with a partition key and sort key that can be different from table primary key. support eventually consistent or strongly consistent reads.
  • Local secondary index – An index that has the same partition key with table primary key, but have a different sort key. only support eventually consistent reads.

Each table in DynamoDB has a limit of 20 global secondary indexes (default limit) and 5 local secondary indexes per table.

Data Type

  • Scalar Types: Number(int, long, double, float), String, Boolean, Bytes, Date.
  • Collection types: Set
  • Support any user defined type by using DynamoDBTypeConverter.

Retrieve Operation

  • Query: must specify a partition key value; the sort key is optional.
  • Scan: lower efficient.

Query

  • A Query operation always returns a result set. will be empty Set if not found.
  • Query results are always sorted by the sort key value. By default, the sort order is ascending. We can set the ScanIndexForward parameter to false to reverse order.
  • A single Query operation can retrieve a maximum of 1 MB of data. This limit applies before any FilterExpression is applied to the results. If LastEvaluatedKey is present in the response and is non-null, we will need to paginate the result set.

Reference

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