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kv: implement SHARED lock strength for unreplicated locks  #91545

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#109638
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kv: implement SHARED lock strength for unreplicated locks #91545
#109638
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arulajmani
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A-kv-transactionsRelating to MVCC and the transactional model.A-read-committedRelated to the introduction of Read CommittedC-enhancementSolution expected to add code/behavior + preserve backward-compat (pg compat issues are exception)P-1Issues/test failures with a fix SLA of 1 monthT-kvKV Team
@arulajmani

Description

@arulajmani
arulajmani
opened on Nov 8, 2022

The lockTable currently only supports the exclusive lock strength, but was designed to support varying degrees of lock strengths. Specifically, it was designed to support both SHARED and UPGRADE (tracked separately in #49684) locking strength as well.

cockroach/pkg/kv/kvserver/concurrency/lock/locking.proto

Lines 40 to 50 in 82b2519

// +-----------+-----------+-----------+-----------+-----------+
// | | None | Shared | Upgrade | Exclusive |
// +-----------+-----------+-----------+-----------+-----------+
// | None | | | | X^† |
// +-----------+-----------+-----------+-----------+-----------+
// | Shared | | | X | X |
// +-----------+-----------+-----------+-----------+-----------+
// | Upgrade | | X | X | X |
// +-----------+-----------+-----------+-----------+-----------+
// | Exclusive | X^† | X | X | X |
// +-----------+-----------+-----------+-----------+-----------+

Additional context

Today SQL accepts syntax of the form SELECT ... FOR SHARE but does not lock any of the rows returned. It should be easy enough to correctly use the SHARED locking strength once the lockTable supports it.

Jira issue: CRDB-21312

Epic CRDB-26544

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A-kv-transactionsRelating to MVCC and the transactional model.A-read-committedRelated to the introduction of Read CommittedC-enhancementSolution expected to add code/behavior + preserve backward-compat (pg compat issues are exception)P-1Issues/test failures with a fix SLA of 1 monthT-kvKV Team

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