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https://issues.apache.org/jira/browse/HIVE-19369?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17019564#comment-17019564
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Denys Kuzmenko edited comment on HIVE-19369 at 1/21/20 2:23 PM:
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Hi [~gopalv], if there was a schema change (i.e. EXCL_DROP) - all
blocked/dependant locks (any type, not only SHARED_READ) should fail fast,
right?
Following scenario (current logic):
{code}alter table acid add columns (b);{code} - acquires EXCLUSIVE lock;
{code}insert into table acid values (1,2,3);{code} - SHARED_READ, waits for
EXCLUSIVE to be released and later throws IndexOutOfBoundsException: Index: 3,
Size: 3
Currently SHARED_WRITE/SEMI_SHARED lock allows only SHARED_READs to go through
and blocks the rest, used for update/delete. If it's an insert (no overwrite) -
SHARED_READ lock is used.
was (Author: dkuzmenko):
Hi [~gopalv], if there was a schema change (i.e. EXCL_DROP) - all
blocked/dependant locks (any type, not only SHARED_READ) should fail fast,
right?
Following scenario (current logic):
{code}alter table acid add columns (b);{code} - acquires EXCLUSIVE lock;
{code}insert into table acid values (1,2,3);{code} - SHARED_READ, waits for
EXCLUSIVE to be released and later throws IndexOutOfBoundsException: Index: 3,
Size: 3
> 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
> Components: Transactions
> Reporter: Gopal Vijayaraghavan
> Assignee: Denys Kuzmenko
> Priority: Major
>
> 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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