ecae097252
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 |
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| configure | ||
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| COPYRIGHT | ||
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PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.