Update the manual and the configuration file

Update the manual and the configuration file
to reflect the new WAL writer architecture.

cfg/core_cfg.cfg_tmpl

@@ -68,9 +68,8 @@ snap_io_rate_limit=0.0, ro
 # Write no more rows in WAL
 rows_per_wal=500000, ro
 
-# Size of the WAL writer request queue: how many outstanding
-# requests for write to disk it can have.
-# Rule of thumb is to set this to the average connection count.
+# OBSOLETE
+# Starting from 1.4.5, this variable has no effect.
 wal_writer_inbox_size=16384, ro
 
 # Defines fiber/data synchronization fsync(2) policy:

doc/user/configuration-reference.xml

@@ -529,22 +529,6 @@ tarantool_box: primary@sessions pri:33013 sec:33014 adm:33015</programlisting>
           locations and moving snapshots to a separate disk.</entry>
         </row>
 
-        <row>
-          <entry xml:id="wal_writer_inbox_size" xreflabel="wal_writer_inbox_size">wal_writer_inbox_size</entry>
-          <entry>integer</entry>
-          <entry>128</entry>
-          <entry>no</entry>
-          <entry>no</entry>
-          <entry>WAL writer is a separate process whose sole
-          purpose is to write the change log to disk. Every
-          incoming data change is sent to this process and
-          queued for write. This parameter affects the size of the
-          user space buffer that WAL writer uses to queue
-          write requests. By default, up to 128 client
-          connections can have pending updates waiting on disk.
-          </entry>
-        </row>
-
         <row>
         <entry>wal_fsync_delay</entry>
         <entry>float</entry>

doc/user/persistence-architecture.xml

@@ -45,7 +45,7 @@ example:
     </para></listitem>
     <listitem><para>
     A message is sent to a separate <quote>wal_writer</quote>
-    process requesting that the change is recorded in the WAL.
+    thread requesting that the change is recorded in the WAL.
     The fiber associate with the current connection is scheduled
     off CPU until an acknowledgment is received from the WAL
     writer.
@@ -60,24 +60,15 @@ example:
 </para>
 
 <para>
-Communication between master and WAL writer processes is asynchronous.
-It is implemented using 'inbox' paradigm, similar to 
-process inboxes in Erlang, from which it was derived.
-Asynchronous but reliable message passing between processes
-allows Tarantool to continue handling requests regardless of disk
-throughput. SELECT performance, provided SELECTs are run in their
-own connections, is unaffected by disk load.
+Communication between master and WAL writer threads is asynchronous.
+It is implemented using an asynchronous FIFO queue.
+Asynchronous but reliable message passing between the master
+and WAL writer threads allows Tarantool to continue handling
+requests regardless of disk throughput. SELECT performance,
+provided SELECTs are run in their own connections, is unaffected
+by disk load.
 </para>
 
-<para>
-The size of each process' inbox is fixed. In particular,
-the WAL writer inbox can hold only <olink targetptr="wal_writer_inbox_size"/>
-messages. This can pose a practical problem when thousands of
-connections perform updates &mdash; the WAL writer inbox can become full.
-Once this happens, the server aborts any update for which
-sending a WAL message has failed with <olink targetptr="ER_WAL_IO"/>
-error.
-</para>
 </section>
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