Whenever more than <varname>bgwriter_flush_after</varname> bytes have
been written by the bgwriter, attempt to force the OS to issue these
writes to the underlying storage. Doing so will limit the amount of
dirty data in the kernel's page cache, reducing the likelihood of
stalls when an fsync is issued at the end of a checkpoint, or when
the OS writes data back in larger batches in the background. Often
that will result in greatly reduced transaction latency, but there
also are some cases, especially with workloads that are bigger than
<xref linkend="guc-shared-buffers">, but smaller than the OS's page
cache, where performance might degrade. This setting may have no
effect on some platforms. <literal>0</literal> disables controlled
writeback. The default is <literal>256Kb</> on Linux, <literal>0</>
otherwise. This parameter can only be set in the
<filename>postgresql.conf</> file or on the server command line.
(plus adjustments for the other gucs)
What about the maximum value?
If the default is in pages, maybe you could state it and afterwards
translate it in size.
"The default is 64 pages on Linux (usually 256Kb)..."
The text could say something about sequential writes performance because
pages are sorted.., but that it is lost for large bases and/or short
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