Gabor Bota created HADOOP-16184:
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Summary: S3Guard: Handle OOB deletions and creation of a file
which has a tombstone marker
Key: HADOOP-16184
URL: https://issues.apache.org/jira/browse/HADOOP-16184
Project: Hadoop Common
Issue Type: Sub-task
Components: fs/s3
Affects Versions: 3.1.0
Reporter: Gabor Bota
When a file is deleted in S3 using S3Guard a tombstone marker will be added for
that file in the MetadataStore. If another process creates the file without
using S3Guard (as an out of band operation - OOB) the file still not be visible
for the client using S3Guard because of the deletion tombstone.
The whole of S3Guard is potentially brittle to
* OOB deletions: we skip it in HADOOP-15999, so no worse, but because the
S3AInputStream retries on FNFE, so as to "debounce" cached 404s, it's
potentially going to retry forever.
* OOB creation of a file which has a deletion tombstone marker.
The things this issue will cover:
* Write a test to simulate that deletion problem, to see what happens. We
ought to have the S3AInputStream retry briefly on that initial GET failing, but
only on that initial one. (after setting "fs.s3a.retry.limit" to something low
& the interval down to 10ms or so to fail fast)
* Sequences
{noformat}
1. create; delete; open; read -> fail after retry
2. create; open, read, delete, read -> fail fast on the second read
{noformat}
The StoreStatistics of the filesystem's IGNORED_ERRORS stat will be increased
on the ignored error, so on sequence 1 will have increased, whereas on sequence
2 it will not have. If either of these tests don't quite fail as expected, we
can disable the tests and continue, at least now with some tests to simulate a
condition we don't have a fix for.
* For both, we just need to have some model of how long it takes for
debouncing to stabilize. Then in this new check, if an FNFE is raised and the
check is happening > (modtime+ debounce-delay) then it's a real FNFE.
This issue is created based on [[email protected]] remarks and comments on
HADOOP-15999.
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