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GetNewOidWithIndex() generates a new OID one by one until it finds one not in the relation. If there are very long runs of consecutive existing OIDs, GetNewOidWithIndex() needs to iterate many times in the loop to find unused OID. Since TOAST table can have a large number of entries and there can be such long runs of OIDs, there is the case where it takes so many iterations to find new OID not in TOAST table. Furthermore if all (i.e., 2^32) OIDs are already used, GetNewOidWithIndex() enters something like busy loop and repeats the iterations until at least one OID is marked as unused. There are some reported troubles caused by a large number of iterations in GetNewOidWithIndex(). For example, when inserting a billion of records into the table, all the backends doing that insertion operation got hang with 100% CPU usage at some point. Previously there was no easy way to detect that GetNewOidWithIndex() failed to find unused OID many times. So, for example, gdb full backtrace of hanged backends needed to be taken, in order to investigate that trouble. This is inconvenient and may not be available in some production environments. To provide easy way for that, this commit makes GetNewOidWithIndex() log that it iterates more than GETNEWOID_LOG_THRESHOLD but have not yet found OID unused in the relation. Also this commit makes it repeat logging with exponentially increasing intervals until it iterates more than GETNEWOID_LOG_MAX_INTERVAL, and makes it finally repeat logging every GETNEWOID_LOG_MAX_INTERVAL unless an unused OID is found. Those macro variables are used not to fill up the server log with the similar messages. In the discusion at pgsql-hackers, there was another idea to report the lots of iterations in GetNewOidWithIndex() via wait event. But since GetNewOidWithIndex() traverses indexes to find unused OID and which will do I/O, acquire locks, etc, which will overwrite the wait event and reset it to nothing once done. So that idea doesn't work well, and we didn't adopt it. Author: Tomohiro Hiramitsu Reviewed-by: Tatsuhito Kasahara, Kyotaro Horiguchi, Tom Lane, Fujii Masao Discussion: https://postgr.es/m/16722-93043fb459a41073@postgresql.org |
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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/.