Concurrency Control

QLDB supports ACID transactions with serializability and it implements optimistic concurrency control (OCC). Similar to other OCC protocols, QLDB allows users to read/update an entry, and then it validates if the current transaction has conflicts with other transactions. But before committing, QLDB needs to verify that the transaction is successfully written into the journal. If yes, then it notifies the clients that the transaction is committed

In both cases of validation failure or journal verification failure, QLDB returns a conflict exception. It’s up to applications to decide whether it needs to rerun the transaction or abort it.

Data Model[03]

Amazon QLDB uses a document-oriented data model Ion, which is originally developed by Amazon for internal use (now open source). It is a superset of JSON in terms of types and validation, as it provides richer data types including int, float, decimal, and timestamp. It can also perform built-in validation by predefined Ion Struct, which not only validates data type and range but also regex expressions if specified.

Ion is a strictly value-based model and supports embedded (hierarchical) documents, but not references.

Indexes[04]

There’s no clear definition of the index type supported in QLDB. However, based on the fact that 1) only queries with equality predicates are improved by indexes 2) composite and range indexes are not supported, it is most likely using hash indexes.

Joins

QLDB only supports inner join.

Query Interface[05]

QLDB supports Amazon’s SQL dialect PartiQL. As its name implies, PartiQL is a small subset of SQL and it supports basic INSERT, SELECT, DELETE, UPDATE, and INNER JOIN.

Here’s a list of clauses that PartiQL does not support yet [DISTINCT, EXISTS, HAVING, LIMIT, UNION, INTERSECT, EXCEPT, PIVOT, UNPIVOT, GROUP BY, ORDER BY, LEFT, RIGHT, OUTER JOIN].

Storage Architecture

QLDB supports monitoring on the disk storage used by journal and indexes.

Storage Model

QLDB stores records as documents, which internally are serialized Ion objects in binary-encoded form.

System Architecture