The documentation of effective_io_concurrency says

    Asynchronous I/O depends on an effective <function>posix_fadvise</>
    function, which some operating systems lack.  If the function is not
    present then setting this parameter to anything but zero will result
    in an error.

This is not correct, because on unsupported systems, it is an error to
set this parameter to anything, including zero, because it is set to

I think this is a mistake.  For example, we allow setting ssl to false
even if SSL support is not compiled in.

I propose the attached patch to correct this.
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 9494439..0229f54 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1892,6 +1892,10 @@ <title>Asynchronous Behavior</title>
          in an error.  On some operating systems (e.g., Solaris), the function
          is present but does not actually do anything.
+        <para>
+         The default is 1 on supported systems, otherwise 0.
+        </para>
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index d208314..d438128 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2269,11 +2269,7 @@ static struct config_int ConfigureNamesInt[] =
 			gettext_noop("Number of simultaneous requests that can be handled efficiently by the disk subsystem."),
 			gettext_noop("For RAID arrays, this should be approximately the number of drive spindles in the array.")
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index c8ff2cb..e6c9e48 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -1288,6 +1288,12 @@ setup_config(void)
 	conflines = replace_token(conflines, "#dynamic_shared_memory_type = posix",
+	conflines = replace_token(conflines,
+							  "#effective_io_concurrency = 1",
+							  "#effective_io_concurrency = 0");
 	snprintf(path, sizeof(path), "%s/postgresql.conf", pg_data);
 	writefile(path, conflines);
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