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When a relation is truncated, shared_buffers needs to be scanned so that any buffers for the relation forks are invalidated in it. Previously, shared_buffers was scanned for each relation forks, i.e., MAIN, FSM and VM, when VACUUM truncated off any empty pages at the end of relation or TRUNCATE truncated the relation in place. Since shared_buffers needed to be scanned multiple times, it could take a long time to finish those commands especially when shared_buffers was large. This commit changes the logic so that shared_buffers is scanned only one time for those three relation forks. Author: Kirk Jamison Reviewed-by: Masahiko Sawada, Thomas Munro, Alvaro Herrera, Takayuki Tsunakawa and Fujii Masao Discussion: https://postgr.es/m/D09B13F772D2274BB348A310EE3027C64E2067@g01jpexmbkw24
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.