Some of the test_decoding regression tests are unstable due to modifying
a sequence. The first increment of a sequence after a checkpoint is
always logged (and thus decoded), which makes the output unpredictable.
The runs are usually much shorter than a checkpoint internal, so these
failures are rare, but we've seen a couple of them on animals that are
either slow or are running with valgrind/clobber cache/...
Fixed by skipping sequence decoding in most tests, with the exception of
the test aimed at testing decoding of sequences.
Reported-by: Amita Kapila
Discussion: https://postgr.es/m/d045f3c2-6cfb-06d3-5540-e63c320df8bc@enterprisedb.com
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