Gopal V created HIVE-19369:
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Summary: Locks: Add new lock implementations for always zero-wait
readers
Key: HIVE-19369
URL: https://issues.apache.org/jira/browse/HIVE-19369
Project: Hive
Issue Type: Improvement
Reporter: Gopal V
Hive Locking with Micro-managed and full-ACID tables needs a better locking
implementation which allows for no-wait readers always.
EXCL_DROP
EXCL_WRITE
SHARED_WRITE
SHARED_READ
Short write-up
EXCL_DROP is a "drop partition" or "drop table" and waits for all others to exit
EXCL_WRITE excludes all writes and will wait for all existing SHARED_WRITE to
exit.
SHARED_WRITE allows all SHARED_WRITES to go through, but will wait for an
EXCL_WRITE & EXCL_DROP (waiting so that you can do drop + insert in different
threads).
SHARED_READ does not wait for any lock - it fails fast for a pending EXCL_DROP,
because even if there is an EXCL_WRITE or SHARED_WRITE pending, there's no
semantic reason to wait for them to succeed before going ahead with a
SHARED_WRITE.
a select * => SHARED_READ
an insert into => SHARED_WRITE
an insert overwrite or MERGE => EXCL_WRITE
a drop table => EXCL_DROP
TODO:
The fate of the compactor needs to be added to this before it is a complete
description.
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