v2-0001-Add-file_extend_method-posix_fallocate-write_zero.patch
text/x-patch
Filename: v2-0001-Add-file_extend_method-posix_fallocate-write_zero.patch
Type: text/x-patch
Part: 0
From 58ec33550147e324e5a6a8793c8e502b9e7065f2 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Sat, 31 May 2025 22:50:22 +1200
Subject: [PATCH v2 1/3] Add file_extend_method=posix_fallocate,write_zeros.
Provide a way to disable the use of posix_fallocate() for relation
files. It was introduced by commit 4d330a61bb1. The new setting
file_extend_method=write_zeros can be used as a workaround for problems
reported from the field:
* BTRFS compression is disabled by the use of posix_fallocate()
* XFS users have reported a few cases of spurious ENOSPC that haven't
been explained yet
The default is file_extend_method=posix_fallocate as before. The new
mode is simlar to PostgreSQL < 16, except that bulk extension writes
zeros for multiple blocks at a time.
Backpatch-through: 16
Reviewed-by: Jakub Wartak <jakub.wartak@enterprisedb.com>
Reported-by: Dimitrios Apostolou <jimis@gmx.net>
Discussion: https://postgr.es/m/b1843124-fd22-e279-a31f-252dffb6fbf2%40gmx.net
---
doc/src/sgml/config.sgml | 37 +++++++++++++++++++
src/backend/storage/file/fd.c | 3 ++
src/backend/storage/smgr/md.c | 21 ++++++++---
src/backend/utils/misc/guc_parameters.dat | 7 ++++
src/backend/utils/misc/guc_tables.c | 9 +++++
src/backend/utils/misc/postgresql.conf.sample | 4 ++
src/include/storage/fd.h | 11 ++++++
7 files changed, 87 insertions(+), 5 deletions(-)
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 405c9689bd0..0b4922b35c4 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2410,6 +2410,43 @@ include_dir 'conf.d'
</listitem>
</varlistentry>
+ <varlistentry id="guc-file-extend-method" xreflabel="file_extend_method">
+ <term><varname>file_extend_method</varname> (<type>enum</type>)
+ <indexterm>
+ <primary><varname>file_extend_method</varname> configuration parameter</primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>
+ Specifies the method used to extend data files during bulk operations
+ such as <command>COPY</command>. The first available option is used as
+ the default, depending on the operating system:
+ <itemizedlist>
+ <listitem>
+ <para>
+ <literal>posix_fallocate</literal> (Unix) uses the standard POSIX
+ interface for allocating disk space, but is missing on some systems.
+ If it is present but the underlying file system doesn't support it,
+ this option silently falls back to <literal>write_zeros</literal>.
+ Current versions of BTRFS are known to disable compression when
+ this option is used.
+ This is the default on systems that have the function.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <literal>write_zeros</literal> extends files by writing out blocks
+ of zero bytes. This is the default on systems that don't have the
+ function <function>posix_fallocate</function>.
+ </para>
+ </listitem>
+ </itemizedlist>
+ The <literal>write_zeros</literal> method is always used when data
+ files are extended by 8 blocks or fewer.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry id="guc-max-notify-queue-pages" xreflabel="max_notify_queue_pages">
<term><varname>max_notify_queue_pages</varname> (<type>integer</type>)
<indexterm>
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 9670e809b72..a2fd55cc408 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -164,6 +164,9 @@ bool data_sync_retry = false;
/* How SyncDataDirectory() should do its job. */
int recovery_init_sync_method = DATA_DIR_SYNC_METHOD_FSYNC;
+/* How data files should be bulk-extended with zeros. */
+int file_extend_method = DEFAULT_FILE_EXTEND_METHOD;
+
/* Which kinds of files should be opened with PG_O_DIRECT. */
int io_direct_flags;
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 71bcdeb6601..df0aa20708d 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -602,13 +602,24 @@ mdzeroextend(SMgrRelation reln, ForkNumber forknum,
* that decision should be made though? For now just use a cutoff of
* 8, anything between 4 and 8 worked OK in some local testing.
*/
- if (numblocks > 8)
+ if (numblocks > 8 &&
+ file_extend_method != FILE_EXTEND_METHOD_WRITE_ZEROS)
{
- int ret;
+ int ret = 0;
- ret = FileFallocate(v->mdfd_vfd,
- seekpos, (pgoff_t) BLCKSZ * numblocks,
- WAIT_EVENT_DATA_FILE_EXTEND);
+#ifdef HAVE_POSIX_FALLOCATE
+ if (file_extend_method == FILE_EXTEND_METHOD_POSIX_FALLOCATE)
+ {
+ ret = FileFallocate(v->mdfd_vfd,
+ seekpos, (pgoff_t) BLCKSZ * numblocks,
+ WAIT_EVENT_DATA_FILE_EXTEND);
+ }
+ else
+#endif
+ {
+ elog(ERROR, "unsupported file_extend_method: %d",
+ file_extend_method);
+ }
if (ret != 0)
{
ereport(ERROR,
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index 3b9d8349078..220a092ef52 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -1039,6 +1039,13 @@
options => 'file_copy_method_options',
},
+{ name => 'file_extend_method', type => 'enum', context => 'PGC_SIGHUP', group => 'RESOURCES_DISK',
+ short_desc => 'Selects the method used for extending data files.',
+ variable => 'file_extend_method',
+ boot_val => 'DEFAULT_FILE_EXTEND_METHOD',
+ options => 'file_extend_method_options',
+},
+
{ name => 'from_collapse_limit', type => 'int', context => 'PGC_USERSET', group => 'QUERY_TUNING_OTHER',
short_desc => 'Sets the FROM-list size beyond which subqueries are not collapsed.',
long_desc => 'The planner will merge subqueries into upper queries if the resulting FROM list would have no more than this many items.',
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index f87b558c2c6..6c65a47a88d 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -80,6 +80,7 @@
#include "storage/bufmgr.h"
#include "storage/bufpage.h"
#include "storage/copydir.h"
+#include "storage/fd.h"
#include "storage/io_worker.h"
#include "storage/large_object.h"
#include "storage/pg_shmem.h"
@@ -491,6 +492,14 @@ static const struct config_enum_entry file_copy_method_options[] = {
{NULL, 0, false}
};
+static const struct config_enum_entry file_extend_method_options[] = {
+#ifdef HAVE_POSIX_FALLOCATE
+ {"posix_fallocate", FILE_EXTEND_METHOD_POSIX_FALLOCATE, false},
+#endif
+ {"write_zeros", FILE_EXTEND_METHOD_WRITE_ZEROS, false},
+ {NULL, 0, false}
+};
+
/*
* Options for enum values stored in other modules
*/
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index dc9e2255f8a..753a42e8ca5 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -179,6 +179,10 @@
# in kilobytes, or -1 for no limit
#file_copy_method = copy # copy, clone (if supported by OS)
+#file_extend_method = posix_fallocate # the default is the first option supported
+ # by the operating system:
+ # posix_fallocate (most Unix-like systems)
+ # write_zeros
#max_notify_queue_pages = 1048576 # limits the number of SLRU pages allocated
# for NOTIFY / LISTEN queue
diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index a8b0c9b3997..f21ac4545a8 100644
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -55,12 +55,23 @@ typedef int File;
#define IO_DIRECT_WAL 0x02
#define IO_DIRECT_WAL_INIT 0x04
+enum FileExtendMethod
+{
+#ifdef HAVE_POSIX_FALLOCATE
+ FILE_EXTEND_METHOD_POSIX_FALLOCATE,
+#endif
+ FILE_EXTEND_METHOD_WRITE_ZEROS,
+};
+
+/* Default to the first available file_extend_method. */
+#define DEFAULT_FILE_EXTEND_METHOD 0
/* GUC parameter */
extern PGDLLIMPORT int max_files_per_process;
extern PGDLLIMPORT bool data_sync_retry;
extern PGDLLIMPORT int recovery_init_sync_method;
extern PGDLLIMPORT int io_direct_flags;
+extern PGDLLIMPORT int file_extend_method;
/*
* This is private to fd.c, but exported for save/restore_backend_variables()
--
2.51.2