Table of Contents

• DynamoDB Overview
• DynamoDB API
• DynamoDB Partitions
• DynamoDB Secondary Indexes
  • GSI
  • LSI
• DynamoDB Consistency
• DynamoDB Capacity & Throughput
• DynamoDB Pricing
• DynamoDB Access and Permissions Based on IAM
• DynamoDB Limits
• DynamoDB Best Practices
• Backup & Restore DynamoDB
• Manipulate DynamoDB Items with awscli
  • Attributes
• DynamoDB.Table.update_item
• DynamoDB.Table.wait_until_exists
• boto3.dynamodb.conditions

DynamoDB Overview tutorial

• Tables like People, Music
• Items like each {..} in Tables
• Attributes like PersonID, LastName, Artist, Price, and so on
• Primary keys are bolded attributes like PersonID, (Artist, SongTitle)
• Primary key can be either a single partition key or a pair of partition key and sort key
• Primary key attribute must be a scalar(like string, number, etc)
• Secondary Indexes like GenreAlbumTitle
• Secondary Indexes can be either Global or Local
• Global consists of a partition key and a sort key that can be different from those on the table
• Local has the same partition key as the table but a different sort key

DynamoDB API reference

CreateTable
DescribeTable
ListTables
UpdateTable
DeleteTable

PutItem
BatchWriteItem (up to 25 items)
GetItem        (uses primary key)
BatchGetItem   (up to 100 items)
Query
Scan
UpdateItem
DeleteItem
BatchWriteItem

ListStreams
DescribeStream
GetShardIterator
GetRecords

Actual using examples are following:

"GetItem"
{
    TableName: "Music",
    Key: {
        "Artist": "No One You Know",
        "SongTitle": "Call Me Today"
    }
}

"Query"
{
    TableName: "Music",
    KeyConditionExpression: "Artist = :a and SongTitle = :t",
    ExpressionAttributeValues: {
        ":a": "No One You Know",
        ":t": "Call Me Today"
    }
}

"Query using Index"
{
    TableName: "Music",
    IndexName: "GenreAndPriceIndex",
    KeyConditionExpression: "Genre = :genre",
    ExpressionAttributeValues: {
        ":genre": "Rock"
    },
};

DynamoDB Partitions discussion

• DynamoDB calculates the hash value of Dog, yielding the partition in which these items are stored.
• DynamoDB then scans the sort key attribute values until it finds Fido.

DynamoDB Secondary Indexes discussion

• This requires separated capacity management from those of its base table

GSI

• A global secondary index is considered "global" because queries on the index can span all of the data in the base table, across all partitions.
• When you create an index, you specify which attributes will be copied, or projected, from the base table to the index.

• DynamoDB maintains indexes automatically.
• In this case, Artist and SongTitle are projected attributes
• Global secondary indexes are composed of partitions.

Attribute Projections

• A projection is the set of attributes that is copied from a table into a secondary index.
• There are three options for attribute projections:
  • KEYS_ONLY
  • INCLUDE
  • ALL

LSI

• A local secondary index is "local" in the sense that every partition of a local secondary index is scoped to a base table partition that has the same partition key value.

DynamoDB Consistency discussion

• DynamoDB supports eventually consistent and strongly consistent reads.

DynamoDB Capacity & Throughput discussion

• Read unit is 4 KB per second (twice when using eventually consistent reads, not strongly consistent reads)
• Write unit is 1 KB per second
• Each unit performs one request per second(if the operation requires the size less than the unit size) . In other words, with 5 read capacity unit, you can handle 5 requests per second.
• Options for determining throughput: Auto scaling, Provisioned, Reserved

Query—reads multiple items that have the same partition key value. All of the items returned are treated as a single read operation, where DynamoDB computes the total size of all items and then rounds up to the next 4 KB boundary. For example, suppose your query returns 10 items whose combined size is 40.8 KB. DynamoDB rounds the item size for the operation to 44 KB. If a query returns 1500 items of 64 bytes each, the cumulative size is 96 KB.

DynamoDB Pricing

• Based on WCU(Write Capacity Unit), RCU(Read Capacity Unit), and Storage

DynamoDB Access and Permissions Based on IAM discussion

If you use dynamodb:Attributes, you must specify the names of all of the primary key and index key attributes for the table and any secondary indexes that are listed the in the policy. Otherwise, DynamoDB can't use these key attributes to perform the requested action.

DynamoDB Limits discussion

DynamoDB Best Practices discussion

Backup & Restore DynamoDB howto

Manipulate DynamoDB Items with awscli howto awscli

#a

an expression attribute name, mostly used with projection expressions

:a

an expression attribute value, mostly used with update expressions

Preventing Overwrites by using condition-expression

aws dynamodb put-item \
    --table-name ProductCatalog \
    --item file://item.json \
    --condition-expression "attribute_not_exists(Id)"

References for operators like attribute_not_exists are here.

Attributes

• Also, the following characters have special meaning in DynamoDB: # (hash) and : (colon).
• Although DynamoDB allows you to use these reserved words and special characters for names, we recommend that you avoid

DynamoDB.Table.update_item reference boto3

key = {'name': name}
expr = ','.join(['SET age = :age',
                 'SET sex = :sex'])
attrs = {':age': 32, ':sex': 'M'}

table.update_item(Key=key,
                  UpdateExpression=','.join(exprs),
                  ExpressionAttributeValues=attrs)

• An expression attribute value(the key of attrs dict) must begin with : and be followed by one or more alphanumeric characters.

DynamoDB.Table.wait_until_exists reference boto3

table.wait_untilexists() doesn't expose the waiter parameters. To manually do the operation using client:

waiter = resource.meta.client.get_waiter('table_exists')
waiter.wait(TableName=table.name, WaiterConfig={'Delay': 5})
setattr(g, attr, table)

boto3.dynamodb.conditions reference boto3

• Use boto3.dynamodb.conditions.Key and boto3.dynamodb.conditions.Attr when making API requests.
• You can use | and & to compose these condition objects.