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Commit5b148706c5exposed functionality that allows multiple processes to use the same replication origin, enabling non-builtin logical replication solutions to implement parallel apply for large transactions. With this functionality, if two backends acquire the same replication origin and one of them resets it first, the acquired_by flag is cleared without acknowledging that another backend is still actively using the origin. This can lead to the origin being unintentionally dropped. If the shared memory for that dropped origin is later reused for a newly created origin, the remaining backend that still holds a pointer to the old memory may inadvertently advance the LSN of a completely different origin, causing unpredictable behavior. Although the underlying issue predates commit5b148706c5, it did not surface earlier because the internal parallel apply worker mechanism correctly coordinated origin resets and drops. This commit resolves the problem by introducing a reference counter for replication origins. The reference count increases when a backend sets the origin and decreases when it resets it. Additionally, the backend that first acquires the origin will not release it until all other backends using the origin have released it as well. The patch also prevents dropping a replication origin when acquired_by is zero but the reference counter is nonzero, covering the scenario where the first session exits without properly releasing the origin. Author: Hou Zhijie <houzj.fnst@fujitsu.com> Author: Hayato Kuroda <kuroda.hayato@fujitsu.com> Reviewed-by: Shveta Malik <shveta.malik@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Discussion: https://postgr.es/m/TY4PR01MB169077EE72ABE9E55BAF162D494B5A@TY4PR01MB16907.jpnprd01.prod.outlook.com Discussion: https://postgr.es/m/CAMPB6wfe4zLjJL8jiZV5kjjpwBM2=rTRme0UCL7Ra4L8MTVdOg@mail.gmail.com
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.