Hi. pg_get_multixact_stats: avoid computing stats with unprivileged users
Previously, pg_get_multixact_stats() called GetMultiXactInfo() and computed the derived "members" and "membersBytes" values unconditionally, before checking whether the caller holds privileges of pg_read_all_stats. When the caller lacks those privileges, the computed values are simply discarded and the function returns an all-NULL row instead, so the work was wasted on every unprivileged call. Move the GetMultiXactInfo() call and the resulting computations into the branch where the values are actually consumed, narrowing the scope of the related local variables to that branch. This matches the usual pattern for privileged stats functions, which skip the underlying work entirely for callers who can't see the result, and avoids touching shared MultiXact state when there is no caller around to observe it. While here, size the memset() that NULLs the output row off sizeof(nulls) rather than *sizeof(bool) * tupdesc->natts*. The two are equivalent today, since nulls is a fixed 4-element array matching the function's declared return type, but relying the memset() with *natts* is an unnecessary dependency. If a column were ever added to the function's SQL definition without a matching update to this array, the old code would silently write past the end of nulls. best regards, Ranier Vilela
refactor-multixact-stats-function-variables-scope.patch
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