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Add a new shmem_request_hook hook.

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Currently, preloaded libraries are expected to request additional
shared memory and LWLocks in _PG_init().  However, it is not unusal
for such requests to depend on MaxBackends, which won't be
initialized at that time.  Such requests could also depend on GUCs
that other modules might change.  This introduces a new hook where
modules can safely use MaxBackends and GUCs to request additional
shared memory and LWLocks.

Furthermore, this change restricts requests for shared memory and
LWLocks to this hook.  Previously, libraries could make requests
until the size of the main shared memory segment was calculated.
Unlike before, we no longer silently ignore requests received at
invalid times.  Instead, we FATAL if someone tries to request
additional shared memory or LWLocks outside of the hook.

Nathan Bossart and Julien Rouhaud

Discussion: https://postgr.es/m/20220412210112.GA2065815%40nathanxps13
Discussion: https://postgr.es/m/Yn2jE/lmDhKtkUdr@paquier.xyz
This commit is contained in:
Robert Haas
2022-05-13 09:31:06 -04:00
parent 8c8d307f82
commit 4f2400cb3f
9 changed files with 81 additions and 38 deletions
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5
src/include/miscadmin.h
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@ -465,6 +465,7 @@ extern void BaseInit(void);
extern PGDLLIMPORT bool IgnoreSystemIndexes;
extern PGDLLIMPORT bool process_shared_preload_libraries_in_progress;
extern PGDLLIMPORT bool process_shared_preload_libraries_done;
extern PGDLLIMPORT bool process_shmem_requests_in_progress;
extern PGDLLIMPORT char *session_preload_libraries_string;
extern PGDLLIMPORT char *shared_preload_libraries_string;
extern PGDLLIMPORT char *local_preload_libraries_string;
@ -478,9 +479,13 @@ extern bool RecheckDataDirLockFile(void);
extern void ValidatePgVersion(const char *path);
extern void process_shared_preload_libraries(void);
extern void process_session_preload_libraries(void);
extern void process_shmem_requests(void);
extern void pg_bindtextdomain(const char *domain);
extern bool has_rolreplication(Oid roleid);
typedef void (*shmem_request_hook_type) (void);
extern PGDLLIMPORT shmem_request_hook_type shmem_request_hook;
/* in executor/nodeHash.c */
extern size_t get_hash_memory_limit(void);