Uploaded image for project: 'Apache Cassandra'
  1. Apache Cassandra
  2. CASSANDRA-15355

Schema push/pull race on continuous schema changes

    XMLWordPrintableJSON

Details

    • Degradation - Slow Use Case
    • Normal
    • Low Hanging Fruit
    • User Report
    • All

    Description

      In https://issues.apache.org/jira/browse/CASSANDRA-5025, pull based schema updates were scheduled 1 minute after the schema change was first visible, so as to prefer the push codepath as much as possible.

      Unfortunately, this does not handle the case where there are many schema changes happening - imagine a scenario where we create a table every 5 seconds for 2 minutes - the first update tasks execute 60 seconds in and the schemas may well be out of sync between nodes at that point.

      In this case, there is some chance that when the task runs, the schemas are out of sync because a subsequent schema update has occurred, and so the same push/pull race has happened.

      A fix is to modify the codepath such that the scheduled task is only run if the other node's schema version is the same as when the task was scheduled. A different (later scheduled) task should run otherwise.

      For us, what we see is that when we have a reasonably large number of changes, a few schema changes can have the unfortunate outcome of causing our nodes to run out of memory and crash - if we have a 30 node cluster, create a table every second for 2 minutes, and for some reason we pause for 10 seconds after 60 seconds with no progress, we can easily end up currently running 300 schema pulls for a single node. These can cause further piling up which causes cascading failures. This change stops that.

      Attachments

        Issue Links

          Activity

            People

              Unassigned Unassigned
              jebaker James Baker
              Votes:
              0 Vote for this issue
              Watchers:
              4 Start watching this issue

              Dates

                Created:
                Updated:

                Time Tracking

                  Estimated:
                  Original Estimate - Not Specified
                  Not Specified
                  Remaining:
                  Remaining Estimate - 0h
                  0h
                  Logged:
                  Time Spent - 10m
                  10m