From 175803f26dd76be274c469f958aef9c391bf88ff Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 17 Jul 2025 19:55:31 -0400 Subject: [PATCH v0] Make type Datum be 8 bytes wide everywhere. This very WIP patch aims to make sizeof(Datum) be 8 on all platforms including 32-bit ones. The objective is to allow USE_FLOAT8_BYVAL to be true everywhere, and in consequence to remove a lot of code that is specific to pass-by-reference handling of float8, int8, etc. In this way we can reduce the maintenance effort involved in supporting 32-bit platforms, without going so far as to actually desupport them. Since Datum is strictly an in-memory concept, this has no impact on on-disk storage, though an initdb or pg_upgrade will be needed to fix affected pg_type.typbyval entries. We can expect that this change will make 32-bit builds a bit slower and more memory-hungry, although being able to use pass-by-value handling of 8-byte types may buy back some of that. But we stopped optimizing for 32-bit cases a long time ago, and this seems like just another step on that path. This initial patch simply forces the correct type definition and USE_FLOAT8_BYVAL setting, and cleans up a couple of minor compiler complaints that ensued. This is sufficient for testing purposes. It does compile cleanly and pass check-world for me on a 32-bit platform. If we pursue this path, we would of course want to remove all the now-dead code (search for mentions of SIZEOF_DATUM and USE_FLOAT8_BYVAL to find likely places to clean up). I have not bothered with that yet. A more interesting question is whether there are comments or calculations that need adjustment. There is probably an effect on the largest array that we can support in 32-bit mode, for example. --- src/backend/storage/ipc/ipc.c | 2 +- src/include/nodes/nodes.h | 8 ++++++-- src/include/pg_config_manual.h | 13 ++++--------- src/include/postgres.h | 13 +++++++------ 4 files changed, 18 insertions(+), 18 deletions(-) diff --git a/src/backend/storage/ipc/ipc.c b/src/backend/storage/ipc/ipc.c index 567739b5be9..2704e80b3a7 100644 --- a/src/backend/storage/ipc/ipc.c +++ b/src/backend/storage/ipc/ipc.c @@ -399,7 +399,7 @@ cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg) before_shmem_exit_list[before_shmem_exit_index - 1].arg == arg) --before_shmem_exit_index; else - elog(ERROR, "before_shmem_exit callback (%p,0x%" PRIxPTR ") is not the latest entry", + elog(ERROR, "before_shmem_exit callback (%p,0x%" PRIx64 ") is not the latest entry", function, arg); } diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h index fbe333d88fa..b2dc380b57b 100644 --- a/src/include/nodes/nodes.h +++ b/src/include/nodes/nodes.h @@ -188,6 +188,8 @@ castNodeImpl(NodeTag type, void *ptr) * ---------------------------------------------------------------- */ +#ifndef FRONTEND + /* * nodes/{outfuncs.c,print.c} */ @@ -198,7 +200,7 @@ extern void outNode(struct StringInfoData *str, const void *obj); extern void outToken(struct StringInfoData *str, const char *s); extern void outBitmapset(struct StringInfoData *str, const struct Bitmapset *bms); -extern void outDatum(struct StringInfoData *str, uintptr_t value, +extern void outDatum(struct StringInfoData *str, Datum value, int typlen, bool typbyval); extern char *nodeToString(const void *obj); extern char *nodeToStringWithLocations(const void *obj); @@ -212,7 +214,7 @@ extern void *stringToNode(const char *str); extern void *stringToNodeWithLocations(const char *str); #endif extern struct Bitmapset *readBitmapset(void); -extern uintptr_t readDatum(bool typbyval); +extern Datum readDatum(bool typbyval); extern bool *readBoolCols(int numCols); extern int *readIntCols(int numCols); extern Oid *readOidCols(int numCols); @@ -235,6 +237,8 @@ extern void *copyObjectImpl(const void *from); */ extern bool equal(const void *a, const void *b); +#endif /* !FRONTEND */ + /* * Typedef for parse location. This is just an int, but this way diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h index 125d3eb5fff..7e1aa422332 100644 --- a/src/include/pg_config_manual.h +++ b/src/include/pg_config_manual.h @@ -74,17 +74,12 @@ #define PARTITION_MAX_KEYS 32 /* - * Decide whether built-in 8-byte types, including float8, int8, and - * timestamp, are passed by value. This is on by default if sizeof(Datum) >= - * 8 (that is, on 64-bit platforms). If sizeof(Datum) < 8 (32-bit platforms), - * this must be off. We keep this here as an option so that it is easy to - * test the pass-by-reference code paths on 64-bit platforms. - * - * Changing this requires an initdb. + * This symbol is now vestigial: built-in 8-byte types, including float8, + * int8, and timestamp, are always passed by value since we require Datum + * to be wide enough to permit that. We continue to define the symbol here + * so as not to unnecessarily break extension code. */ -#if SIZEOF_VOID_P >= 8 #define USE_FLOAT8_BYVAL 1 -#endif /* diff --git a/src/include/postgres.h b/src/include/postgres.h index 8a41a668687..f2d3ee5af3b 100644 --- a/src/include/postgres.h +++ b/src/include/postgres.h @@ -58,15 +58,18 @@ /* * A Datum contains either a value of a pass-by-value type or a pointer to a - * value of a pass-by-reference type. Therefore, we require: - * - * sizeof(Datum) == sizeof(void *) == 4 or 8 + * value of a pass-by-reference type. Therefore, we must have + * sizeof(Datum) >= sizeof(void *). No current or foreseeable Postgres + * platform has pointers wider than 8 bytes, and standardizing on Datum being + * exactly 8 bytes has advantages in reducing cross-platform differences. * * The functions below and the analogous functions for other types should be used to * convert between a Datum and the appropriate C type. */ -typedef uintptr_t Datum; +typedef uint64_t Datum; + +#define SIZEOF_DATUM 8 /* * A NullableDatum is used in places where both a Datum and its nullness needs @@ -83,8 +86,6 @@ typedef struct NullableDatum /* due to alignment padding this could be used for flags for free */ } NullableDatum; -#define SIZEOF_DATUM SIZEOF_VOID_P - /* * DatumGetBool * Returns boolean value of a datum. -- 2.43.5