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Make superuser.c maintain a simple one-entry cache holding the superuser

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status of the most recently queried userid.  Since the common pattern is
many successive queries about the same user (ie, the current user) this
can save a lot of syscache probes.
This commit is contained in:
Tom Lane 2005-05-29 20:38:06 +00:00
parent db86f29617
commit 299c442077
1 changed files with 59 additions and 10 deletions
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69
src/backend/utils/misc/superuser.c
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@ -2,7 +2,11 @@
*
* superuser.c
* The superuser() function. Determines if user has superuser privilege.
* Also, a function to check for the owner (datdba) of a database.
*
* All code should use either of these two functions to find out
* whether a given user is a superuser, rather than examining
* pg_shadow.usesuper directly, so that the escape hatch built in for
* the single-user case works.
*
*
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
@ -10,26 +14,33 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/misc/superuser.c,v 1.30 2004/12/31 22:02:45 pgsql Exp $
* $PostgreSQL: pgsql/src/backend/utils/misc/superuser.c,v 1.31 2005/05/29 20:38:06 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/heapam.h"
#include "catalog/pg_shadow.h"
#include "commands/dbcommands.h"
#include "utils/inval.h"
#include "utils/syscache.h"
#include "miscadmin.h"
/*
* In common cases the same userid (ie, the session or current ID) will
* be queried repeatedly. So we maintain a simple one-entry cache for
* the status of the last requested userid. The cache can be flushed
* at need by watching for cache update events on pg_shadow.
*/
static AclId last_userid = 0; /* 0 == cache not valid */
static bool last_userid_is_super = false;
static bool userid_callback_registered = false;
static void UseridCallback(Datum arg, Oid relid);
/*
* The Postgres user running this command has Postgres superuser privileges
*
* All code should use either of these two functions to find out
* whether a given user is a superuser, rather than evaluating
* pg_shadow.usesuper directly, so that the escape hatch built in for
* the single-user case works.
*/
bool
superuser(void)
@ -38,16 +49,24 @@ superuser(void)
}
/*
* The specified userid has Postgres superuser privileges
*/
bool
superuser_arg(AclId userid)
{
bool result = false;
bool result;
HeapTuple utup;
/* Quick out for cache hit */
if (AclIdIsValid(last_userid) && last_userid == userid)
return last_userid_is_super;
/* Special escape path in case you deleted all your users. */
if (!IsUnderPostmaster && userid == BOOTSTRAP_USESYSID)
return true;
/* OK, look up the information in pg_shadow */
utup = SearchSysCache(SHADOWSYSID,
Int32GetDatum(userid),
0, 0, 0);
@ -56,5 +75,35 @@ superuser_arg(AclId userid)
result = ((Form_pg_shadow) GETSTRUCT(utup))->usesuper;
ReleaseSysCache(utup);
}
else
{
/* Report "not superuser" for invalid userids */
result = false;
}
/* If first time through, set up callback for cache flushes */
if (!userid_callback_registered)
{
CacheRegisterSyscacheCallback(SHADOWSYSID,
UseridCallback,
(Datum) 0);
userid_callback_registered = true;
}
/* Cache the result for next time */
last_userid = userid;
last_userid_is_super = result;
return result;
}
/*
* UseridCallback
* Syscache inval callback function
*/
static void
UseridCallback(Datum arg, Oid relid)
{
/* Invalidate our local cache in case user's superuserness changed */
last_userid = 0;
}