In addition to the added functions, the pg_buffercache_evict() function now
shows whether the buffer was flushed.
pg_buffercache_evict_relation(): Evicts all shared buffers in a
relation at once.
pg_buffercache_evict_all(): Evicts all shared buffers at once.
Both functions provide mechanism to evict multiple shared buffers at
once. They are designed to address the inefficiency of repeatedly calling
pg_buffercache_evict() for each individual buffer, which can be time-consuming
when dealing with large shared buffer pools. (e.g., ~477ms vs. ~2576ms for
16GB of fully populated shared buffers).
These functions are intended for developer testing and debugging
purposes and are available to superusers only.
Minimal tests for the new functions are included. Also, there was no test for
pg_buffercache_evict(), test for this added too.
No new extension version is needed, as it was already increased this release
by ba2a3c2302f.
Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Aidar Imamov <a.imamov@postgrespro.ru>
Reviewed-by: Joseph Koshakow <koshy44@gmail.com>
Discussion: https://postgr.es/m/CAN55FZ0h_YoSqqutxV6DES1RW8ig6wcA8CR9rJk358YRMxZFmw%40mail.gmail.com
Introduces a new view pg_buffercache_numa, showing NUMA memory nodes
for individual buffers. For each buffer the view returns an entry for
each memory page, with the associated NUMA node.
The database blocks and OS memory pages may have different size - the
default block size is 8KB, while the memory page is 4K (on x86). But
other combinations are possible, depending on configure parameters,
platform, etc. This means buffers may overlap with multiple memory
pages, each associated with a different NUMA node.
To determine the NUMA node for a buffer, we first need to touch the
memory pages using pg_numa_touch_mem_if_required, otherwise we might get
status -2 (ENOENT = The page is not present), indicating the page is
either unmapped or unallocated.
The view may be relatively expensive, especially when accessed for the
first time in a backend, as it touches all memory pages to get reliable
information about the NUMA node. This may also force allocation of the
shared memory.
Author: Jakub Wartak <jakub.wartak@enterprisedb.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: https://postgr.es/m/CAKZiRmxh6KWo0aqRqvmcoaX2jUxZYb4kGp3N%3Dq1w%2BDiH-696Xw%40mail.gmail.com
It was pointed out that pg_buffercache_summary()'s report of
the overall average usage count isn't that useful, and what
would be more helpful in many cases is to report totals for
each possible usage count. Add a new function to do it like
that. Since pg_buffercache 1.4 is already new for v16,
we don't need to create a new extension version; we'll just
define this as part of 1.4.
Nathan Bossart
Discussion: https://postgr.es/m/20230130233040.GA2800702@nathanxps13
Using pg_buffercache_summary() is significantly cheaper than querying
pg_buffercache and summarizing in SQL.
Author: Melih Mutlu <m.melihmutlu@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Reviewed-by: Zhang Mingli <zmlpostgres@gmail.com>
Discussion: https://postgr.es/m/CAGPVpCQAXYo54Q%3D8gqBsS%3Du0uk9qhnnq4%2B710BtUhUisX1XGEg%40mail.gmail.com
We can't check the output of this view very closely without
creating portability headaches, but we can make sure that
the number of rows is as-expected. In any case, this is
sufficient to exercise all the C code within, which is a
lot better than the 0% coverage we had before.
DongWook Lee
Discussion: https://postgr.es/m/CAAcByaLCHGJB7qAENEcx9D09UL=w4ma+yijwF_-1MSqQZ9wK6Q@mail.gmail.com
