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Because we assume that int64 and double have the same alignment requirement, AIX's default behavior that alignof(double) = 4 while alignof(int64) = 8 is a headache. There are two issues: 1. We align both int8 and float8 tuple columns per ALIGNOF_DOUBLE, which is an ancient choice that can't be undone without breaking pg_upgrade and creating some subtle SQL-level compatibility issues too. However, the cost of that is just some marginal inefficiency in fetching int8 values, which can't be too awful if the platform architects were willing to pay the same costs for fetching float8s. So our decision is to leave that alone. This patch makes our alignment choices the same as they were pre-v17, namely that ALIGNOF_DOUBLE and ALIGNOF_INT64_T are whatever the compiler prefers and then MAXIMUM_ALIGNOF is the larger of the two. (On all supported platforms other than AIX, all three values will be the same.) 2. We need to overlay C structs onto catalog tuples, and int8 fields in those struct declarations may not be aligned to match this rule. In the old branches we had some annoying rules about ordering catalog columns to avoid alignment problems, but nobody wants to resurrect those. However, there's a better answer: make the compiler construe those struct declarations the way we need it to by using the pack(N) pragma. This requires no manual effort to maintain going forward; we only have to insert the pragma into all the catalog *.h files. (As the catalogs stand at this writing, nothing actually changes because we've not moved any affected columns since v16; hence no catversion bump is required. The point of this is to not have to worry about the issue going forward.) We did not have this option when the AIX port was first made. This patch depends on the C99 feature _Pragma(), as well as the pack(N) pragma which dates to somewhere around gcc 4.0, and probably doesn't exist in xlc at all. But now that we've agreed to toss xlc support out the window, there doesn't seem to be a reason not to go this way. In passing, I got rid of LONGALIGN[_DOWN] along with the configure probes for ALIGNOF_LONG. We were not using those anywhere and it seems highly unlikely that we'd do so in future. Instead supply INT64ALIGN[_DOWN], which isn't used either but at least could have a good reason to be used. Discussion: https://postgr.es/m/1127261.1769649624@sss.pgh.pa.us
77 lines
2.9 KiB
C
77 lines
2.9 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_description.h
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* definition of the "description" system catalog (pg_description)
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*
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* Because the contents of this table are taken from the *.dat files
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* of other catalogs, there is no pg_description.dat file. The initial
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* contents are assembled by genbki.pl and loaded during initdb.
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*
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* NOTE: an object is identified by the OID of the row that primarily
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* defines the object, plus the OID of the table that that row appears in.
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* For example, a function is identified by the OID of its pg_proc row
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* plus the pg_class OID of table pg_proc. This allows unique identification
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* of objects without assuming that OIDs are unique across tables.
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*
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* Since attributes don't have OIDs of their own, we identify an attribute
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* comment by the objoid+classoid of its parent table, plus an "objsubid"
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* giving the attribute column number. "objsubid" must be zero in a comment
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* for a table itself, so that it is distinct from any column comment.
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* Currently, objsubid is unused and zero for all other kinds of objects,
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* but perhaps it might be useful someday to associate comments with
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* constituent elements of other kinds of objects (arguments of a function,
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* for example).
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*
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*
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* Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/catalog/pg_description.h
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*
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* NOTES
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* The Catalog.pm module reads this file and derives schema
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* information.
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PG_DESCRIPTION_H
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#define PG_DESCRIPTION_H
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#include "catalog/genbki.h"
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#include "catalog/pg_description_d.h" /* IWYU pragma: export */
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/* ----------------
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* pg_description definition. cpp turns this into
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* typedef struct FormData_pg_description
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* ----------------
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*/
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BEGIN_CATALOG_STRUCT
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CATALOG(pg_description,2609,DescriptionRelationId)
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{
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Oid objoid; /* OID of object itself */
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Oid classoid; /* OID of table containing object */
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int32 objsubid; /* column number, or 0 if not used */
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#ifdef CATALOG_VARLEN /* variable-length fields start here */
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text description BKI_FORCE_NOT_NULL; /* description of object */
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#endif
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} FormData_pg_description;
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END_CATALOG_STRUCT
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/* ----------------
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* Form_pg_description corresponds to a pointer to a tuple with
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* the format of pg_description relation.
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* ----------------
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*/
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typedef FormData_pg_description * Form_pg_description;
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DECLARE_TOAST(pg_description, 2834, 2835);
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DECLARE_UNIQUE_INDEX_PKEY(pg_description_o_c_o_index, 2675, DescriptionObjIndexId, pg_description, btree(objoid oid_ops, classoid oid_ops, objsubid int4_ops));
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/* We do not use BKI_LOOKUP here because it causes problems for genbki.pl */
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DECLARE_FOREIGN_KEY((classoid), pg_class, (oid));
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#endif /* PG_DESCRIPTION_H */
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