DynamoDB - Part1

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Here is first part of the DynamoDB tutorial/summary.

Terminology

Table - Group of items, keys and indexes

Item - is ROW of data stored in table.

Primary key - Key used to uniquely identify an item (or) row in a table. Two types of primary keys exists in DynamoDB.

   1. Simple Primary Key, ONLY one field/attribute in your table you would like to use to uniquely identify the item/row.

Another name for “simple primary key” IS “partition key”.

Because DynamoDB uses this field/attribute as input for hash function in determining where to store an item (physically on disk), another name for this key is “partition key”.

Refer “Data Storage” section to learn about tables & partitions.      

   2. Composite Primary Key, is combination of “Primary Key field” + Another field/attribute of the table you would like to use to store/retrieve data in sorted order. Because this key has more than one key, we call it as “composite” primary key.

Provisioned throughput/capacity -> is the configuration you define while creating tables. This is combination of “Read capacity units (RCU)” and “Write capacity units (WCU)”.

Data storage

DynamoDB stores table data into “one or more” partitions.

A partition is storage allocated for table data on SSDs (solid state drives).

DynamoDB uses “primary key (or) partition key” + hash function to determine which partition particular table item should be stored.

   

1. If your table has “simple primary key”, this field/attribute will be passed to hash function to determine which partition item should be stored to.

2. If your table has “composite primary key (partition key + sort key), then partition key will be passed to hash function to determine which partition item should be stored to. “Sort key” will be used to store the items in sorted order with-in the partition.

DynamoDB handles partition management (creating new partitions, replicating partitions, deleting partitions etc.,). Users don’t need to perform any special actions/configurations.

Throughput configured is per table.

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