Again fix initialization of auto-tuned effective_cache_size.
The previous method was overly complex and underly correct; in particular, by assigning the default value with PGC_S_OVERRIDE, it prevented later attempts to change the setting in postgresql.conf, as noted by Jeff Janes. We should just assign the default value with source PGC_S_DYNAMIC_DEFAULT, which will have the desired priority relative to the boot_val as well as user-set values. There is still a gap in this method: if there's an explicit assignment of effective_cache_size = -1 in the postgresql.conf file, and that assignment appears before shared_buffers is assigned, the code will substitute 4 times the bootstrap default for shared_buffers, and that value will then persist (since it will have source PGC_S_FILE). I don't see any very nice way to avoid that though, and it's not a case to be expected in practice. The existing comments in guc-file.l look forward to a redesign of the DYNAMIC_DEFAULT mechanism; if that ever happens, we should consider this case as one of the things we'd like to improve.
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@ -4107,16 +4107,7 @@ check_effective_cache_size(int *newval, void **extra, GucSource source)
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if (*newval <= 0)
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{
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/*
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* If we haven't yet changed the initial default of -1, just let it
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* be. We'll fix it later on during GUC initialization, when
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* set_default_effective_cache_size is called. (If we try to do it
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* immediately, we may not be looking at the final value of NBuffers.)
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*/
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if (effective_cache_size == -1)
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return true;
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/*
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* Otherwise, substitute the auto-tune value, being wary of overflow.
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* Substitute the auto-tune value, being wary of overflow.
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*/
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if (NBuffers < INT_MAX / 4)
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*newval = NBuffers * 4;
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@ -4130,22 +4121,22 @@ check_effective_cache_size(int *newval, void **extra, GucSource source)
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}
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/*
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* initialize effective_cache_size at the end of GUC startup
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* Initialize effective_cache_size at the end of GUC startup, or when
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* a setting in postgresql.conf is removed.
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*
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* Note: check_effective_cache_size() will have been called when the boot_val
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* was installed, but we will not have known the final value of NBuffers at
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* that time, which is why this has to be called at the end of GUC startup.
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*/
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void
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set_default_effective_cache_size(void)
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{
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/*
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* If the value of effective_cache_size is still -1 (or zero), replace it
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* with the auto-tune value.
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* We let check_effective_cache_size() compute the actual setting. Note
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* that this call is a no-op if the user has supplied a setting (since
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* that will have a higher priority than PGC_S_DYNAMIC_DEFAULT).
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*/
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if (effective_cache_size <= 0)
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{
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/* disable the short-circuit in check_effective_cache_size */
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effective_cache_size = 0;
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/* and let check_effective_cache_size() compute the setting */
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SetConfigOption("effective_cache_size", "-1",
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PGC_POSTMASTER, PGC_S_OVERRIDE);
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}
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SetConfigOption("effective_cache_size", "-1",
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PGC_POSTMASTER, PGC_S_DYNAMIC_DEFAULT);
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Assert(effective_cache_size > 0);
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}
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@ -298,6 +298,7 @@ ProcessConfigFile(GucContext context)
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{
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InitializeGUCOptionsFromEnvironment();
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pg_timezone_abbrev_initialize();
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set_default_effective_cache_size();
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/* this selects SQL_ASCII in processes not connected to a database */
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SetConfigOption("client_encoding", GetDatabaseEncodingName(),
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PGC_BACKEND, PGC_S_DYNAMIC_DEFAULT);
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