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  1. Core Server
  2. SERVER-20328

Allow secondary reads while applying oplog entries

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Details

    • Improvement
    • Status: Closed
    • Major - P3
    • Resolution: Duplicate
    • None
    • None
    • Replication, Storage
    • None

    Description

      Currently replication applies batches of oplog entries holding a lock to ensure that no reads can consume data which is not in the same causal order as the primary.

      Instead of locking and blocking readers we can instead use a snapshot for reads from the last consistent replication state and essentially hide all writes until we reach a new consistent state. In addition to detaching replication writes from affecting readers (both users and other replicas) this also allows storage engines to optimize writing of replicated data to improve performance and reduce IO, since all replicated data is transient and disposable until committed.

      Attachments

        Issue Links

          duplicates

          New Feature - A new feature of the product, which has yet to be developed. SERVER-34192 Secondary reads during batch applications

          • Critical - P2 - Crashes, loss of data, severe memory leak.
          • Closed
          is duplicated by

          Bug - A problem which impairs or prevents the functions of the product. SERVER-21858 A high throughput update workload in a replica set can cause starvation of secondary reads

          • Major - P3 - Major loss of function.
          • Closed

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-24661 Secondary block reader a very long time when replay oplog

          • Major - P3 - Major loss of function.
          • Closed
          is related to

          Bug - A problem which impairs or prevents the functions of the product. SERVER-25168 Foreground index build blocks all R/W on ALL database on a sharded cluster with secondaryPreferred read preference

          • Major - P3 - Major loss of function.
          • Closed

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-5729 Special-case concurrency model for oplog, make reads not block as much

          • Major - P3 - Major loss of function.
          • Closed

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-6883 index creation on secondaries need not block readers

          • Major - P3 - Major loss of function.
          • Closed

          Question - SERVER-29123 Why is ParallelBatchWriterMode used when Applying Oplogs

          • Critical - P2 - Crashes, loss of data, severe memory leak.
          • Closed

          Question - SERVER-31359 when large inserts into mongo, lots of global lock occur

          • Major - P3 - Major loss of function.
          • Closed
          related to

          New Feature - A new feature of the product, which has yet to be developed. WT-2649 Some way to indicate valid points in the WT log

          • Major - P3 - Major loss of function.
          • Closed

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-21862 Use record store directly to read from oplog for replication

          • Major - P3 - Major loss of function.
          • Closed

          Activity

            People

              louis.williams@mongodb.com Louis Williams
              scotthernandez Scott Hernandez (Inactive)
              Votes:
              22 Vote for this issue
              Watchers:
              36 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved: