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postgresql/src/include/utils/guc_hooks.h
Alvaro Herrera 53c2a97a92
Improve performance of subsystems on top of SLRU 
More precisely, what we do here is make the SLRU cache sizes
configurable with new GUCs, so that sites with high concurrency and big
ranges of transactions in flight (resp. multixacts/subtransactions) can
benefit from bigger caches.  In order for this to work with good
performance, two additional changes are made:

1. the cache is divided in "banks" (to borrow terminology from CPU
   caches), and algorithms such as eviction buffer search only affect
   one specific bank.  This forestalls the problem that linear searching
   for a specific buffer across the whole cache takes too long: we only
   have to search the specific bank, whose size is small.  This work is
   authored by Andrey Borodin.

2. Change the locking regime for the SLRU banks, so that each bank uses
   a separate LWLock.  This allows for increased scalability.  This work
   is authored by Dilip Kumar.  (A part of this was previously committed as
   d172b717c6f4.)

Special care is taken so that the algorithms that can potentially
traverse more than one bank release one bank's lock before acquiring the
next.  This should happen rarely, but particularly clog.c's group commit
feature needed code adjustment to cope with this.  I (Álvaro) also added
lots of comments to make sure the design is sound.

The new GUCs match the names introduced by bcdfa5f2e2 in the
pg_stat_slru view.

The default values for these parameters are similar to the previous
sizes of each SLRU.  commit_ts, clog and subtrans accept value 0, which
means to adjust by dividing shared_buffers by 512 (so 2MB for every 1GB
of shared_buffers), with a cap of 8MB.  (A new slru.c function
SimpleLruAutotuneBuffers() was added to support this.)  The cap was
previously 1MB for clog, so for sites with more than 512MB of shared
memory the total memory used increases, which is likely a good tradeoff.
However, other SLRUs (notably multixact ones) retain smaller sizes and
don't support a configured value of 0.  These values based on
shared_buffers may need to be revisited, but that's an easy change.

There was some resistance to adding these new GUCs: it would be better
to adjust to memory pressure automatically somehow, for example by
stealing memory from shared_buffers (where the caches can grow and
shrink naturally).  However, doing that seems to be a much larger
project and one which has made virtually no progress in several years,
and because this is such a pain point for so many users, here we take
the pragmatic approach.

Author: Andrey Borodin <x4mmm@yandex-team.ru>
Author: Dilip Kumar <dilipbalaut@gmail.com>
Reviewed-by: Amul Sul, Gilles Darold, Anastasia Lubennikova,
	Ivan Lazarev, Robert Haas, Thomas Munro, Tomas Vondra,
	Yura Sokolov, Васильев Дмитрий (Dmitry Vasiliev).
Discussion: https://postgr.es/m/2BEC2B3F-9B61-4C1D-9FB5-5FAB0F05EF86@yandex-team.ru
Discussion: https://postgr.es/m/CAFiTN-vzDvNz=ExGXz6gdyjtzGixKSqs0mKHMmaQ8sOSEFZ33A@mail.gmail.com
2024-02-28 17:05:31 +01:00

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/*-------------------------------------------------------------------------
*
* guc_hooks.h
* Declarations of per-variable callback functions used by GUC.
*
* These functions are scattered throughout the system, but we
* declare them all here to avoid having to propagate guc.h into
* a lot of unrelated header files.
*
* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
*
* src/include/utils/guc_hooks.h
*
*-------------------------------------------------------------------------
*/
#ifndef GUC_HOOKS_H
#define GUC_HOOKS_H 1
#include "utils/guc.h"
/*
* See guc.h for the typedefs that these hook functions should match
* (GucBoolCheckHook and so on).
*
* Please keep the declarations in order by GUC variable name.
*/
extern bool check_application_name(char **newval, void **extra,
GucSource source);
extern void assign_application_name(const char *newval, void *extra);
extern const char *show_archive_command(void);
extern bool check_autovacuum_max_workers(int *newval, void **extra,
GucSource source);
extern bool check_autovacuum_work_mem(int *newval, void **extra,
GucSource source);
extern bool check_vacuum_buffer_usage_limit(int *newval, void **extra,
GucSource source);
extern bool check_backtrace_functions(char **newval, void **extra,
GucSource source);
extern void assign_backtrace_functions(const char *newval, void *extra);
extern bool check_bonjour(bool *newval, void **extra, GucSource source);
extern bool check_canonical_path(char **newval, void **extra, GucSource source);
extern void assign_checkpoint_completion_target(double newval, void *extra);
extern bool check_client_connection_check_interval(int *newval, void **extra,
GucSource source);
extern bool check_client_encoding(char **newval, void **extra, GucSource source);
extern void assign_client_encoding(const char *newval, void *extra);
extern bool check_cluster_name(char **newval, void **extra, GucSource source);
extern bool check_commit_ts_buffers(int *newval, void **extra,
GucSource source);
extern const char *show_data_directory_mode(void);
extern bool check_datestyle(char **newval, void **extra, GucSource source);
extern void assign_datestyle(const char *newval, void *extra);
extern bool check_debug_io_direct(char **newval, void **extra, GucSource source);
extern void assign_debug_io_direct(const char *newval, void *extra);
extern bool check_default_table_access_method(char **newval, void **extra,
GucSource source);
extern bool check_default_tablespace(char **newval, void **extra,
GucSource source);
extern bool check_default_text_search_config(char **newval, void **extra, GucSource source);
extern void assign_default_text_search_config(const char *newval, void *extra);
extern bool check_default_with_oids(bool *newval, void **extra,
GucSource source);
extern bool check_effective_io_concurrency(int *newval, void **extra,
GucSource source);
extern bool check_huge_page_size(int *newval, void **extra, GucSource source);
extern const char *show_in_hot_standby(void);
extern bool check_locale_messages(char **newval, void **extra, GucSource source);
extern void assign_locale_messages(const char *newval, void *extra);
extern bool check_locale_monetary(char **newval, void **extra, GucSource source);
extern void assign_locale_monetary(const char *newval, void *extra);
extern bool check_locale_numeric(char **newval, void **extra, GucSource source);
extern void assign_locale_numeric(const char *newval, void *extra);
extern bool check_locale_time(char **newval, void **extra, GucSource source);
extern void assign_locale_time(const char *newval, void *extra);
extern bool check_log_destination(char **newval, void **extra,
GucSource source);
extern void assign_log_destination(const char *newval, void *extra);
extern const char *show_log_file_mode(void);
extern bool check_log_stats(bool *newval, void **extra, GucSource source);
extern bool check_log_timezone(char **newval, void **extra, GucSource source);
extern void assign_log_timezone(const char *newval, void *extra);
extern const char *show_log_timezone(void);
extern bool check_maintenance_io_concurrency(int *newval, void **extra,
GucSource source);
extern void assign_maintenance_io_concurrency(int newval, void *extra);
extern bool check_max_connections(int *newval, void **extra, GucSource source);
extern bool check_max_wal_senders(int *newval, void **extra, GucSource source);
extern bool check_max_slot_wal_keep_size(int *newval, void **extra,
GucSource source);
extern void assign_max_wal_size(int newval, void *extra);
extern bool check_max_worker_processes(int *newval, void **extra,
GucSource source);
extern bool check_max_stack_depth(int *newval, void **extra, GucSource source);
extern void assign_max_stack_depth(int newval, void *extra);
extern bool check_multixact_member_buffers(int *newval, void **extra,
GucSource source);
extern bool check_multixact_offset_buffers(int *newval, void **extra,
GucSource source);
extern bool check_notify_buffers(int *newval, void **extra, GucSource source);
extern bool check_primary_slot_name(char **newval, void **extra,
GucSource source);
extern bool check_random_seed(double *newval, void **extra, GucSource source);
extern void assign_random_seed(double newval, void *extra);
extern const char *show_random_seed(void);
extern bool check_recovery_prefetch(int *new_value, void **extra,
GucSource source);
extern void assign_recovery_prefetch(int new_value, void *extra);
extern bool check_recovery_target(char **newval, void **extra,
GucSource source);
extern void assign_recovery_target(const char *newval, void *extra);
extern bool check_recovery_target_lsn(char **newval, void **extra,
GucSource source);
extern void assign_recovery_target_lsn(const char *newval, void *extra);
extern bool check_recovery_target_name(char **newval, void **extra,
GucSource source);
extern void assign_recovery_target_name(const char *newval, void *extra);
extern bool check_recovery_target_time(char **newval, void **extra,
GucSource source);
extern void assign_recovery_target_time(const char *newval, void *extra);
extern bool check_recovery_target_timeline(char **newval, void **extra,
GucSource source);
extern void assign_recovery_target_timeline(const char *newval, void *extra);
extern bool check_recovery_target_xid(char **newval, void **extra,
GucSource source);
extern void assign_recovery_target_xid(const char *newval, void *extra);
extern bool check_role(char **newval, void **extra, GucSource source);
extern void assign_role(const char *newval, void *extra);
extern const char *show_role(void);
extern bool check_search_path(char **newval, void **extra, GucSource source);
extern void assign_search_path(const char *newval, void *extra);
extern bool check_serial_buffers(int *newval, void **extra, GucSource source);
extern bool check_session_authorization(char **newval, void **extra, GucSource source);
extern void assign_session_authorization(const char *newval, void *extra);
extern void assign_session_replication_role(int newval, void *extra);
extern void assign_stats_fetch_consistency(int newval, void *extra);
extern bool check_ssl(bool *newval, void **extra, GucSource source);
extern bool check_stage_log_stats(bool *newval, void **extra, GucSource source);
extern bool check_subtrans_buffers(int *newval, void **extra,
GucSource source);
extern bool check_synchronous_standby_names(char **newval, void **extra,
GucSource source);
extern void assign_synchronous_standby_names(const char *newval, void *extra);
extern void assign_synchronous_commit(int newval, void *extra);
extern void assign_syslog_facility(int newval, void *extra);
extern void assign_syslog_ident(const char *newval, void *extra);
extern void assign_tcp_keepalives_count(int newval, void *extra);
extern const char *show_tcp_keepalives_count(void);
extern void assign_tcp_keepalives_idle(int newval, void *extra);
extern const char *show_tcp_keepalives_idle(void);
extern void assign_tcp_keepalives_interval(int newval, void *extra);
extern const char *show_tcp_keepalives_interval(void);
extern void assign_tcp_user_timeout(int newval, void *extra);
extern const char *show_tcp_user_timeout(void);
extern bool check_temp_buffers(int *newval, void **extra, GucSource source);
extern bool check_temp_tablespaces(char **newval, void **extra,
GucSource source);
extern void assign_temp_tablespaces(const char *newval, void *extra);
extern bool check_timezone(char **newval, void **extra, GucSource source);
extern void assign_timezone(const char *newval, void *extra);
extern const char *show_timezone(void);
extern bool check_timezone_abbreviations(char **newval, void **extra,
GucSource source);
extern void assign_timezone_abbreviations(const char *newval, void *extra);
extern bool check_transaction_buffers(int *newval, void **extra, GucSource source);
extern bool check_transaction_deferrable(bool *newval, void **extra, GucSource source);
extern bool check_transaction_isolation(int *newval, void **extra, GucSource source);
extern bool check_transaction_read_only(bool *newval, void **extra, GucSource source);
extern void assign_transaction_timeout(int newval, void *extra);
extern const char *show_unix_socket_permissions(void);
extern bool check_wal_buffers(int *newval, void **extra, GucSource source);
extern bool check_wal_consistency_checking(char **newval, void **extra,
GucSource source);
extern void assign_wal_consistency_checking(const char *newval, void *extra);
extern bool check_wal_segment_size(int *newval, void **extra, GucSource source);
extern void assign_wal_sync_method(int new_wal_sync_method, void *extra);
#endif /* GUC_HOOKS_H */
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