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AllocateFile(), AllocateDir(), and some sister routines share a small array for remembering requests, so that the files can be closed on transaction failure. Previously that array had a fixed size, MAX_ALLOCATED_DESCS (32). While historically that had seemed sufficient, Steve Toutant pointed out that this meant you couldn't scan more than 32 file_fdw foreign tables in one query, because file_fdw depends on the COPY code which uses AllocateFile(). There are probably other cases, or will be in the future, where this nonconfigurable limit impedes users. We can't completely remove any such limit, at least not without a lot of work, since each such request requires a kernel file descriptor and most platforms limit the number we can have. (In principle we could "virtualize" these descriptors, as fd.c already does for the main VFD pool, but not without an additional layer of overhead and a lot of notational impact on the calling code.) But we can at least let the array size be configurable. Hence, change the code to allow up to max_safe_fds/2 allocated file requests. On modern platforms this should allow several hundred concurrent file_fdw scans, or more if one increases the value of max_files_per_process. To go much further than that, we'd need to do some more work on the data structure, since the current code for closing requests has potentially O(N^2) runtime; but it should still be all right for request counts in this range. Back-patch to 9.1 where contrib/file_fdw was introduced. |
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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: http://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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.