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Originally, we palloc'd this buffer just barely big enough to hold the largest xlog record seen so far. It turns out that that can result in valgrind complaints, because some compilers will emit code that assumes it can safely fetch padding bytes at the end of a struct, and those padding bytes were unallocated so far as aset.c was concerned. We can fix that by MAXALIGN'ing the palloc request size, ensuring that it is big enough to include any possible padding that might've been omitted from the on-disk record. An additional objection to the original coding is that it could result in many repeated palloc cycles, in the worst case where we see a series of gradually larger xlog records. We can ameliorate that cheaply by imposing a minimum buffer size that's large enough for most xlog records. BLCKSZ/2 was chosen after a bit of discussion. In passing, remove an obsolete comment in struct xl_heap_new_cid that the combocid field is free due to alignment considerations. Perhaps that was true at some point, but it's not now. Back-patch to 9.5 where this code came in. Discussion: https://postgr.es/m/E1eHa4J-0006hI-Q8@gemulon.postgresql.org
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. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.