Shreyansh's Everything Notebook 📖

Dealing with Stale Reads

Dec 11, 20242 min read

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Making eventual consistency less shit !!

Reading your own writes:

  1. Let’s say I write to the DB and read from the replica, I might get inconsistent result if the data is not propagated to the DBs.
  2. To solve this
    1. We can read from the same DB.
    2. In case we’re reading from a replica, we can ask the DB if data from the particular timestamp is synced or not before reading from that replica.

  • On the right, Data replication is implemented using Versioning and Timestamps(to know more read below).

Monotonic reads:

Monotonic reads are particularly relevant in distributed systems with data replication, where data is copied and maintained across multiple nodes. Here’s how monotonic reads can be implemented:

  1. Versioning and Timestamps: Each data item can be versioned or timestamped. When a process reads a data item, it records the version or timestamp. Subsequent reads ensure they only return the same or newer versions.

  2. Client-side Caching: Clients can cache the latest version of data items they have read. Any future read requests first check the cached version to ensure monotonicity.

  3. Read Repair Mechanisms: During a read operation, if a node detects that it has an older version of the data item compared to the version the client has already seen, it can initiate a read repair process to fetch and return the latest version from other nodes.

Consistent prefix reads:

Consistent Prefix Reads is a consistency model in distributed databases that ensures all read operations see writes in a sequential order. In other words, if a series of writes (A, B, C) are made to a database, a read will see either A, A-B, or A-B-C, but never A-C or B-C. This model guarantees the order of operations but does not necessarily provide the most recent data immediately.

Use Cases

  • E-commerce Applications: Ensuring order consistency in updates like price changes, stock updates, and product descriptions.
  • Social Media Platforms: Ensuring posts and comments appear in the correct sequence across different regions.
  • Collaborative Tools: Ensuring document edits are seen in the correct order, even if not all edits are immediately visible.

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