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As noted by Tom Lane the improvements in 4b4b680c3d6 had the problem that in some situations we searched, entered and modified entries in the private refcount hash while holding a spinlock. I had tried to keep the logic entirely local to PinBuffer_Locked(), but that's not really possible given it's called with a spinlock held... Besides being disadvantageous from a performance point of view, this also has problems with error handling safety. If we failed inserting an entry into the hashtable due to an out of memory error, we'd error out with a held spinlock. Not good. Change the way private refcounts are manipulated: Before a buffer can be tracked an entry has to be reserved using ReservePrivateRefCountEntry(); then, if a entry is not found using GetPrivateRefCountEntry(), it can be entered with NewPrivateRefCountEntry(). Also take advantage of the fact that PinBuffer_Locked() currently is never called for buffers that already have been pinned by the current backend and don't search the private refcount entries for preexisting local pins. That results in a small, but measurable, performance improvement. Additionally make ReleaseBuffer() always call UnpinBuffer() for shared buffers. That avoids duplicating work in an eventual UnpinBuffer() call that already has been done in ReleaseBuffer() and also saves some code. Per discussion with Tom Lane. Discussion: 15028.1418772313@sss.pgh.pa.us
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. 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/.