1. 16 May, 2020 1 commit
  2. 28 Apr, 2020 1 commit
  3. 27 Apr, 2020 1 commit
    • Oran Agra's avatar
      Keep track of meaningful replication offset in replicas too · 4447ddc8
      Oran Agra authored
      Now both master and replicas keep track of the last replication offset
      that contains meaningful data (ignoring the tailing pings), and both
      trim that tail from the replication backlog, and the offset with which
      they try to use for psync.
      
      the implication is that if someone missed some pings, or even have
      excessive pings that the promoted replica has, it'll still be able to
      psync (avoid full sync).
      
      the downside (which was already committed) is that replicas running old
      code may fail to psync, since the promoted replica trims pings form it's
      backlog.
      
      This commit adds a test that reproduces several cases of promotions and
      demotions with stale and non-stale pings
      
      Background:
      The mearningful offset on the master was added recently to solve a problem were
      the master is left all alone, injecting PINGs into it's backlog when no one is
      listening and then gets demoted and tries to replicate from a replica that didn't
      have any of the PINGs (or at least not the last ones).
      
      however, consider this case:
      master A has two replicas (B and C) replicating directly from it.
      there's no traffic at all, and also no network issues, just many pings in the
      tail of the backlog. now B gets promoted, A becomes a replica of B, and C
      remains a replica of A. when A gets demoted, it trims the pings from its
      backlog, and successfully replicate from B. however, C is still aware of
      these PINGs, when it'll disconnect and re-connect to A, it'll ask for something
      that's not in the backlog anymore (since A trimmed the tail of it's backlog),
      and be forced to do a full sync (something it didn't have to do before the
      meaningful offset fix).
      
      Besides that, the psync2 test was always failing randomly here and there, it
      turns out the reason were PINGs. Investigating it shows the following scenario:
      
      cycle 1: redis #1 is master, and all the rest are direct replicas of #1
      cycle 2: redis #2 is promoted to master, #1 is a replica of #2 and #3 is replica of #1
      now we see that when #1 is demoted it prints:
      17339:S 21 Apr 2020 11:16:38.523 * Using the meaningful offset 3929963 instead of 3929977 to exclude the final PINGs (14 bytes difference)
      17339:S 21 Apr 2020 11:16:39.391 * Trying a partial resynchronization (request e2b3f8817735fdfe5fa4626766daa938b61419e5:3929964).
      17339:S 21 Apr 2020 11:16:39.392 * Successful partial resynchronization with master.
      and when #3 connects to the demoted #2, #2 says:
      17339:S 21 Apr 2020 11:16:40.084 * Partial resynchronization not accepted: Requested offset for secondary ID was 3929978, but I can reply up to 3929964
      
      so the issue here is that the meaningful offset feature saved the day for the
      demoted master (since it needs to sync from a replica that didn't get the last
      ping), but it didn't help one of the other replicas which did get the last ping.
      4447ddc8
  4. 05 Mar, 2020 1 commit
    • Oran Agra's avatar
      fix for flaky psync2 test · 27641ee4
      Oran Agra authored
      *** [err]: PSYNC2: total sum of full synchronizations is exactly 4 in tests/integration/psync2.tcl
      Expected 5 == 4 (context: type eval line 6 cmd {assert {$sum == 4}} proc ::test)
      
      issue was that sometime the test got an unexpected full sync since it
      tried to switch to the replica before it was in sync with it's master.
      27641ee4
  5. 05 May, 2019 1 commit
    • Oran Agra's avatar
      make replication tests more stable on slow machines · ba809f26
      Oran Agra authored
      solving few replication related tests race conditions which fail on slow machines
      
      bugfix in slave buffers test: since the test is executed twice, each time with
      a different commands count, the threshold for the delta can't be a constant.
      ba809f26
  6. 11 Sep, 2018 1 commit
  7. 31 Jul, 2018 1 commit
  8. 30 Nov, 2017 1 commit
  9. 29 Nov, 2016 3 commits
  10. 28 Nov, 2016 2 commits
    • antirez's avatar
      PSYNC2: stop sending newlines to sub-slaves when master is down. · eab865a0
      antirez authored
      This actually includes two changes:
      
      1) No newlines to take the master-slave link up when the upstream master
      is down. Doing this is dangerous because the sub-slave often is received
      replication protocol for an half-command, so can't receive newlines
      without desyncing the replication link, even with the code in order to
      cancel out the bytes that PSYNC2 was using. Moreover this is probably
      also not needed/sane, because anyway the slave can keep serving
      requests, and because if it's configured to don't serve stale data, it's
      a good idea, actually, to break the link.
      
      2) When a +CONTINUE with a different ID is received, we now break
      connection with the sub-slaves: they need to be notified as well. This
      was part of the original specification but for some reason it was not
      implemented in the code, and was alter found as a PSYNC2 bug in the
      integration testing.
      eab865a0
    • antirez's avatar
      PSYNC2: Test (WIP). · 16559a02
      antirez authored
      This is the PSYNC2 test that helped find issues in the code, and that
      still can show a protocol desync from time to time. Work is in progress
      in order to find the issue. For now the test is not enabled in "make
      test" and must be run manually.
      16559a02