333f586372
In fcb9c977aa5 I included an assertion in BufferLockConditional() to detect if a conditional lock acquisition is done on a buffer that we already have locked. The assertion was added in the course of adding other assertions. Unfortunately I failed to realize that some of our code relies on such lock acquisitions to silently fail. E.g. spgist and nbtree may try to conditionally lock an already locked buffer when acquiring a empty buffer. LWLockAcquireConditional(), which was previously used to implement ConditionalLockBuffer(), does not have such an assert. Instead of just removing the assert, and relying on the lock acquisition to fail due to the buffer already locked, this commit changes the behaviour of conditional content lock acquisition to fail if the current backend has any pre-existing lock on the buffer, even if the lock modes would not conflict. The reason for that is that we currently do not have space to track multiple lock acquisitions on a single buffer. Allowing multiple locks on the same buffer by a backend also seems likely to lead to bugs. There is only one non-self-exclusive conditional content lock acquisition, in GetVictimBuffer(), but it only is used if the target buffer is not pinned and thus can't already be locked by the current backend. Reported-by: Alexander Lakhin <exclusion@gmail.com> Discussion: https://postgr.es/m/90bd2cbb-49ce-4092-9f61-5ac2ab782c94@gmail.com
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
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