Elastic Database tools glossary

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Applies to: Azure SQL Database

The following terms are defined for the Elastic Database tools. The tools are used to manage shard maps, and include the client library, the split-merge tool, elastic pools, and queries.

These terms are used in Adding a shard using Elastic Database tools and Using the RecoveryManager class to fix shard map problems.

Elastic Scale terms

Database: A database in Azure SQL Database.

Data dependent routing: The functionality that enables an application to connect to a shard given a specific sharding key. See Data dependent routing. Compare to Multi-Shard Query.

Global shard map: The map between sharding keys and their respective shards within a shard set. The global shard map is stored in the shard map manager. Compare to local shard map.

List shard map: A shard map in which sharding keys are mapped individually. Compare to Range Shard Map.

Local shard map: Stored on a shard, the local shard map contains mappings for the shardlets that reside on the shard.

Multi-shard query: The ability to issue a query against multiple shards; results sets are returned using UNION ALL semantics (also known as "fan-out query"). Compare to data dependent routing.

Multi-tenant and Single-tenant: This shows a single-tenant database and a multi-tenant database:

Screenshot that shows a single-tenant database and a multi-tenant database.

Here is a representation of sharded single and multi-tenant databases.

Single and multi-tenant databases

Range shard map: A shard map in which the shard distribution strategy is based on multiple ranges of contiguous values.

Reference tables: Tables that are not sharded but are replicated across shards. For example, zip codes can be stored in a reference table.

Shard: A database in Azure SQL Database that stores data from a sharded data set.

Shard elasticity: The ability to perform both horizontal scaling and vertical scaling.

Sharded tables: Tables that are sharded, i.e., whose data is distributed across shards based on their sharding key values.

Sharding key: A column value that determines how data is distributed across shards. The value type can be one of the following: int, bigint, varbinary, or uniqueidentifier.

Shard set: The collection of shards that are attributed to the same shard map in the shard map manager.

Shardlet: All of the data associated with a single value of a sharding key on a shard. A shardlet is the smallest unit of data movement possible when redistributing sharded tables.

Shard map: The set of mappings between sharding keys and their respective shards.

Shard map manager: A management object and data store that contains the shard map(s), shard locations, and mappings for one or more shard sets.

Diagram shows a shard map manager associated with shardmaps_global, shards_global, and shard_mappings_global.

Verbs

Horizontal scaling: The act of scaling out (or in) a collection of shards by adding or removing shards to a shard map, as shown below.

Horizontal and vertical scaling

Merge: The act of moving shardlets from two shards to one shard and updating the shard map accordingly.

Shardlet move: The act of moving a single shardlet to a different shard.

Shard: The act of horizontally partitioning identically structured data across multiple databases based on a sharding key.

Split: The act of moving several shardlets from one shard to another (typically new) shard. A sharding key is provided by the user as the split point.

Vertical Scaling: The act of scaling up (or down) the compute size of an individual shard. For example, changing a shard from Standard to Premium (which results in more computing resources).

Related content

Not using elastic database tools yet? Check out our Getting Started Guide.