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It seems incorrect to assume that the list of CkptSortItems can never contain duplicate page numbers: concurrent activity could result in some page getting dropped from a low-numbered buffer and later loaded into a high-numbered buffer while BufferSync is scanning the buffer pool. If that happened, the comparator would give self-inconsistent results, potentially confusing qsort(). Saving one comparison step is not worth possibly getting the sort wrong. So far as I can tell, nothing would actually go wrong given our current implementation of qsort(). It might get a bit slower than expected if there were a large number of duplicates of one value, but that's surely a probability-epsilon case. Still, the comment is wrong, and if we ever switched to another sort implementation it might be less forgiving. In passing, avoid casting away const-ness of the argument pointers; I've not seen any compiler complaints from that, but it seems likely that some compilers would not like it. Back-patch to 9.6 where this code came in, just in case I've underestimated the possible consequences. Discussion: https://postgr.es/m/18437.1515607610@sss.pgh.pa.us |
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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. 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/.