IndexShardTests.testDocStats fails sporadically #32766
Description
Example build failure:
https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+6.x+periodic/2518/console
Reproduction line (does not reproduce locally):
./gradlew :server:test \
-Dtests.seed=A8914B40F85100F0 \
-Dtests.class=org.elasticsearch.index.shard.IndexShardTests \
-Dtests.method="testDocStats" \
-Dtests.security.manager=true \
-Dtests.locale=th-TH \
-Dtests.timezone=Asia/Thimphu
Example relevant log:
09:35:38 1> [2561-08-09T15:35:33,402][INFO ][o.e.i.s.IndexShardTests ] [testDocStats] before test
09:35:38 1> [2561-08-09T15:35:33,495][INFO ][o.e.i.s.IndexShardTests ] [testDocStats] after test
09:35:38 FAILURE 0.11s J0 | IndexShardTests.testDocStats <<< FAILURES!
09:35:38 > Throwable #1: java.lang.AssertionError:
09:35:38 > Expected: <12L>
09:35:38 > but: was <0L>
09:35:38 > at __randomizedtesting.SeedInfo.seed([A8914B40F85100F0:F184FAEDD87CEDDD]:0)
09:35:38 > at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
09:35:38 > at org.elasticsearch.index.shard.IndexShardTests.testDocStats(IndexShardTests.java:2442)
09:35:38 > at java.lang.Thread.run(Thread.java:748)
Frequency: First failure dates back to February, with another isolated failure on 26th of June, then spikes on July 26-27 with 7 failures across branches and much more on PR builds. Failed at least once per day in the last couple of days.