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Tom Lane
4647ac1423
pg_mkdir_p creates each missing path component with a stat() followed
by mkdir(). If the stat() reports the component as absent but another
process creates it in the window before this process's mkdir(), mkdir()
fails with EEXIST and pg_mkdir_p treated that as a hard error -- unlike
"mkdir -p", which is meant to be idempotent and race-tolerant.
This shows up when several processes concurrently create paths that
share an ancestor directory: for example, parallel initdb runs whose
data directories live under a common temporary directory. One process
wins the race to create the shared ancestor and the others fail with
could not create directory "...": File exists
Fix this race condition by first trying mkdir() and only attempting
stat() if it fails with EEXIST.
On Windows, there's an additional problem: stat() opens a file handle
and participates in share-mode locking, which means it can transiently
fail on a directory another process is concurrently creating. Use
GetFileAttributes() instead: it requests only FILE_READ_ATTRIBUTES
and is exempt from share-mode denial, so it reliably sees a
concurrently-created directory.
I (tgl) also chose to back-patch 039f7ee0f's effects on this function,
so that pgmkdirp.c remains identical in all live branches.
Author: Andrew Dunstan <andrew@dunslane.net>
Co-authored-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/3ca004de-e49b-4471-b8aa-fd656e70f68c@dunslane.net
Backpatch-through: 14
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/.