From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org, alex work <alexwork033@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Subject: Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs
Date: Fri, 22 Mar 2024 09:47:39 -0500
Message-ID: <20240322144739.GA2321246@nathanxps13> (raw)
In-Reply-To: <806361.1711069194@sss.pgh.pa.us>
References: <CAGvXd3OSMbJQwOSc-Tq-Ro1CAz=vggErdSG7pv2s6vmmTOLJSg@mail.gmail.com>
<341186.1711037256@sss.pgh.pa.us>
<619340.1711050134@sss.pgh.pa.us>
<642442.1711053105@sss.pgh.pa.us>
<20240321204012.GA1992418@nathanxps13>
<20240322005139.GA2060816@nathanxps13>
<806361.1711069194@sss.pgh.pa.us>
On Thu, Mar 21, 2024 at 08:59:54PM -0400, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
>> On Thu, Mar 21, 2024 at 03:40:12PM -0500, Nathan Bossart wrote:
>>> On Thu, Mar 21, 2024 at 04:31:45PM -0400, Tom Lane wrote:
>>>> I don't think we have any really cheap way to de-duplicate the role
>>>> OIDs, especially seeing that it has to be done on-the-fly within the
>>>> collection loop, and the order of roles_list is at least potentially
>>>> interesting. Not sure how to make further progress without a lot of
>>>> work.
>
>>> Assuming these are larger lists, this might benefit from optimizations
>>> involving SIMD intrinsics.
>
>> Never mind. With the reproduction script, I'm only seeing a ~2%
>> improvement with my patches.
>
> Yeah, you cannot beat an O(N^2) problem by throwing SIMD at it.
I apparently had some sort of major brain fade when I did this because I
didn't apply your hashing patch when I ran this SIMD test. With it
applied, I see a speedup of ~39%, which makes a whole lot more sense to me.
If I add the Bloom patch (updated with your suggestions), I get another
~73% improvement from there, and a much smaller regression in the role
creation portion.
hash hash+simd hash+simd+bloom
create 1.27 1.27 1.28
grant 0.18 0.11 0.03
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.comAttachments:bloom_v2.patch (text/x-diff, 2.3K) downloaddiff --git a/src/backend/utils/adt/acl.c b/src/backend/utils/adt/acl.cindex cf5d08576a..4952dc9c1e 100644--- a/src/backend/utils/adt/acl.c+++ b/src/backend/utils/adt/acl.c@@ -36,6 +36,7 @@
#include "common/hashfn.h"
#include "foreign/foreign.h"
#include "funcapi.h"
+#include "lib/bloomfilter.h"
#include "lib/qunique.h"
#include "miscadmin.h"
#include "utils/acl.h"
@@ -4946,6 +4947,7 @@ roles_is_member_of(Oid roleid, enum RoleRecurseType type,
ListCell *l;
List *new_cached_roles;
MemoryContext oldctx;
+ bloom_filter *bf = NULL;
Assert(OidIsValid(admin_of) == PointerIsValid(admin_role));
if (admin_role != NULL)
@@ -5023,16 +5025,46 @@ roles_is_member_of(Oid roleid, enum RoleRecurseType type,
* graph, we must test for having already seen this role. It is
* legal for instance to have both A->B and A->C->B.
*/
- roles_list = list_append_unique_oid(roles_list, otherid);+ if ((bf && bloom_lacks_element(bf, (unsigned char *) &otherid, sizeof(Oid))) ||+ !list_member_oid(roles_list, otherid))+ {+ if (bf == NULL && list_length(roles_list) > 1000)+ {+ bf = bloom_create(1024 * 1024, work_mem, 0);+ foreach_oid(role, roles_list)+ bloom_add_element(bf, (unsigned char *) &role, sizeof(Oid));+ }+ roles_list = lappend_oid(roles_list, otherid);+ if (bf)+ bloom_add_element(bf, (unsigned char *) &otherid, sizeof(Oid));+ }
}
ReleaseSysCacheList(memlist);
/* implement pg_database_owner implicit membership */
if (memberid == dba && OidIsValid(dba))
- roles_list = list_append_unique_oid(roles_list,- ROLE_PG_DATABASE_OWNER);+ {+ Oid dbowner = ROLE_PG_DATABASE_OWNER;++ if ((bf && bloom_lacks_element(bf, (unsigned char *) &dbowner, sizeof(Oid))) ||+ !list_member_oid(roles_list, dbowner))+ {+ if (bf == NULL && list_length(roles_list) > 1000)+ {+ bf = bloom_create(1024 * 1024, work_mem, 0);+ foreach_oid(role, roles_list)+ bloom_add_element(bf, (unsigned char *) &role, sizeof(Oid));+ }+ roles_list = lappend_oid(roles_list, dbowner);+ if (bf)+ bloom_add_element(bf, (unsigned char *) &dbowner, sizeof(Oid));+ }+ }
}
+ if (bf)+ bloom_free(bf);+
/*
* Copy the completed list into TopMemoryContext so it will persist.
*/
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To: pgsql-general@postgresql.org
Cc: nathandbossart@gmail.com, tgl@sss.pgh.pa.us, alexwork033@gmail.com, robertmhaas@gmail.com
Subject: Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs
In-Reply-To: <20240322144739.GA2321246@nathanxps13>
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