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Up to now checkpoints were written in the order they're in the BufferDescriptors. That's nearly random in a lot of cases, which performs badly on rotating media, but even on SSDs it causes slowdowns. To avoid that, sort checkpoints before writing them out. We currently sort by tablespace, relfilenode, fork and block number. One of the major reasons that previously wasn't done, was fear of imbalance between tablespaces. To address that balance writes between tablespaces. The other prime concern was that the relatively large allocation to sort the buffers in might fail, preventing checkpoints from happening. Thus pre-allocate the required memory in shared memory, at server startup. This particularly makes it more efficient to have checkpoint flushing enabled, because that'll often result in a lot of writes that can be coalesced into one flush. Discussion: alpine.DEB.2.10.1506011320000.28433@sto Author: Fabien Coelho and Andres Freund
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/.