Uploaded image for project: 'WiredTiger'
  1. WiredTiger
  2. WT-2042

Slowdown with named snapshots

        Details

        • Type: Improvement
        • Status: Resolved
        • Priority: Critical - P2
        • Resolution: Fixed
        • Affects Version/s: None
        • Fix Version/s: WT2.7.0
        • Labels:
          None
        • # Replies:
          15
        • Last comment by Customer:
          true

          Description

          The mongodb test jstests/noPassthroughWithMongod/indexbg_interrupts.js takes significantly longer with snapshots enabled (42 min vs 1 min). Most of the time is spent in the convertToCapped command. Profiling shows that the vast majority of the time is spent iterating the update lists in __rec_txn_read and __wt_row_modify.

          My theory is that the existence of a snapshot is preventing splitting a page. This workload creates a new collection and inserts ~100k records into it without creating new snapshots or retiring old ones. I think that the linear scans are causing this to be an O(N^2) operation.

            Issue Links

            depends on

            New Feature - A new feature of the product, which has yet to be developed. WT-1967 Support long-running snapshot readers

            • Major - P3 - Major loss of function.
            • Resolved
            is depended on by

            Improvement - An improvement or enhancement to an existing feature or task. SERVER-19910 Reenable convertToCapped testing in indexbg_interrupts.js

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

            Improvement - An improvement or enhancement to an existing feature or task. SERVER-20479 WiredTiger changes for MongoDB 3.0.7

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

              Activity

              • Comments
              Ascending order - Click to sort in descending order
              9 older comments
              Hide
              Permalink
              xgen-internal-githook Githook User added a comment -

              Author:

              {u'username': u'keithbostic', u'name': u'Keith Bostic', u'email': u'keith.bostic@mongodb.com'}

              Message: WT-2042 Only try to evict tombstones that are visible to all readers.

              Merge pull request #2196 from wiredtiger/WT-2042

              (cherry picked from commit 5ab26af636f8c6a5a86200d1c18f249d0749fc9a)
              Branch: mongodb-3.0
              https://github.com/wiredtiger/wiredtiger/commit/08e884609d9be6bcff8bb580e3ce85ef2b5a6b5d

              Show
              xgen-internal-githook Githook User added a comment - Author: {u'username': u'keithbostic', u'name': u'Keith Bostic', u'email': u'keith.bostic@mongodb.com'} Message: WT-2042 Only try to evict tombstones that are visible to all readers. Merge pull request #2196 from wiredtiger/ WT-2042 (cherry picked from commit 5ab26af636f8c6a5a86200d1c18f249d0749fc9a) Branch: mongodb-3.0 https://github.com/wiredtiger/wiredtiger/commit/08e884609d9be6bcff8bb580e3ce85ef2b5a6b5d
              Hide
              Permalink
              michael.cahill Michael Cahill added a comment -

              Note that the changes so far on the WiredTiger side improve the situation, but there is still inefficiency at the beginning of the tree where lots of tombstones accumulate. Changing MongoDB to track the first live record in the tree for capped delete operations removes the remaining inefficiency, but we will investigate a more general approach in WiredTiger first.

              Show
              michael.cahill Michael Cahill added a comment - Note that the changes so far on the WiredTiger side improve the situation, but there is still inefficiency at the beginning of the tree where lots of tombstones accumulate. Changing MongoDB to track the first live record in the tree for capped delete operations removes the remaining inefficiency, but we will investigate a more general approach in WiredTiger first.
              Hide
              Permalink
              xgen-internal-githook Githook User added a comment -

              Author:

              {u'username': u'RedBeard0531', u'name': u'Mathias Stearn', u'email': u'mathias@10gen.com'}

              Message: SERVER-19213 Disable convertToCapped testing in indexbg_interrupts.js

              It is way too slow with the replSnapshotThread enabled due to WT-2042. It
              will be re-enabled as part of SERVER-19910.
              Branch: master
              https://github.com/mongodb/mongo/commit/1abd9f24692b8fc95767f2575594fb232cba2157

              Show
              xgen-internal-githook Githook User added a comment - Author: {u'username': u'RedBeard0531', u'name': u'Mathias Stearn', u'email': u'mathias@10gen.com'} Message: SERVER-19213 Disable convertToCapped testing in indexbg_interrupts.js It is way too slow with the replSnapshotThread enabled due to WT-2042 . It will be re-enabled as part of SERVER-19910 . Branch: master https://github.com/mongodb/mongo/commit/1abd9f24692b8fc95767f2575594fb232cba2157
              Hide
              Permalink
              pasette Dan Pasette added a comment -

              Michael, seems like this issue can be resolved as the WT portion of the work is complete, and the rest will be done in the integration layer with SERVER-21008.

              Show
              pasette Dan Pasette added a comment - Michael, seems like this issue can be resolved as the WT portion of the work is complete, and the rest will be done in the integration layer with SERVER-21008 .
              Hide
              Permalink
              michael.cahill Michael Cahill added a comment -

              Agreed, I'll resolve.

              Show
              michael.cahill Michael Cahill added a comment - Agreed, I'll resolve.

                People

                • Votes:
                  0 Vote for this issue
                  Watchers:
                  5 Start watching this issue

                  Dates

                  • Created:
                    Updated:
                    Resolved:
                    Days since reply:
                    1 year, 34 weeks, 5 days ago
                    Date of 1st Reply: