mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-12-21 08:29:39 +08:00
da8a716089
We have for a long time checked the head pointer of each of the backend's proclock lists and skipped acquiring the corresponding locktable partition lock if the head pointer was NULL. This was safe enough in the days when proclock lists were changed only by the owning backend, but it is pretty questionable now that the fast-path patch added cases where backends add entries to other backends' proclock lists. However, we don't really wish to revert to locking each partition lock every time, because in simple transactions that would add a lot of useless lock/unlock cycles on already-heavily-contended LWLocks. Fortunately, the only way that another backend could be modifying our proclock list at this point would be if it was promoting a formerly fast-path lock of ours; and any such lock must be one that we'd decided not to delete in the previous loop over the locallock table. So it's okay if we miss seeing it in this loop; we'd just decide not to delete it again. However, once we've detected a non-empty list, we'd better re-fetch the list head pointer after acquiring the partition lock. This guards against possibly fetching a corrupt-but-non-null pointer if pointer fetch/store isn't atomic. It's not clear if any practical architectures are like that, but we've never assumed that before and don't wish to start here. In any case, the situation certainly deserves a code comment. While at it, refactor the partition traversal loop to use a for() construct instead of a while() loop with goto's. Back-patch, just in case the risk is real and not hypothetical. |
||
|---|---|---|
| config | ||
| contrib | ||
| doc | ||
| src | ||
| .dir-locals.el | ||
| .gitattributes | ||
| .gitignore | ||
| aclocal.m4 | ||
| configure | ||
| configure.in | ||
| COPYRIGHT | ||
| GNUmakefile.in | ||
| Makefile | ||
| README | ||
| README.git | ||
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/.