Re: Allow logical replication to copy tables in binary format

Here are some review comments for v15-0001

======
doc/src/sgml/logical-replication.sgml

1.
+   target table. However, logical replication in binary format is
more restrictive,
+   see <literal>binary</literal> option of
+   <link linkend="sql-createsubscription"><command>CREATE
SUBSCRIPTION</command></link>
+   for more details.

IMO  (and Chat-GPT agrees) the new text should be 2 sentences.

Also, I changed "more details" --> "details" because none are provided here,.

SUGGESTION
However, logical replication in <literal>binary</literal> format is
more restrictive. See the binary option of <link
linkend="sql-createsubscription"><command>CREATE
SUBSCRIPTION</command></link> for details.

======
doc/src/sgml/ref/alter_subscription.sgml

2.
+         <para>
+          See <literal>binary</literal> option of <xref
linkend="sql-createsubscription"/>
+          for details of copying pre-existing data in binary format.
+         </para>

Should the link should be defined more like you did above using the
<command> markup to get the better font?

SUGGESTION (also minor rewording)
See the <literal>binary</literal> option of <link
linkend="sql-createsubscription"><command>CREATE
SUBSCRIPTION</command></link> for details about copying pre-existing
data in binary format.

======
doc/src/sgml/ref/create_subscription.sgml

3.
          <para>
-          Specifies whether the subscription will request the publisher to
-          send the data in binary format (as opposed to text).
-          The default is <literal>false</literal>.
-          Even when this option is enabled, only data types having
-          binary send and receive functions will be transferred in binary.
+          Specifies whether the subscription will request the publisher to send
+          the data in binary format (as opposed to text). The default is
+          <literal>false</literal>. Any initial table synchronization copy
+          (see <literal>copy_data</literal>) also uses the same format. Binary
+          format can be faster than the text format, but it is less portable
+          across machine architectures and PostgreSQL versions. Binary format
+          is very data type specific; for example, it will not allow copying
+          from a smallint column to an integer column, even though that would
+          work fine in text format. Even when this option is enabled, only data
+          types having binary send and receive functions will be transferred in
+          binary. Note that the initial synchronization requires all data types
+          to have binary send and receive functions, otherwise the
synchronization
+          will fail (see <xref linkend="sql-createtype"/> for more about
+          send/receive functions).
          </para>

IMO that part saying "from a smallint column to an integer column"
should have <type></type> markups for "smallint" and "integer".

======
src/backend/replication/logical/tablesync.c

4.
+ /*
+ * The binary option for replication is supported since v14
+ */
+ if (walrcv_server_version(LogRepWorkerWalRcvConn) >= 140000 &&
+ MySubscription->binary)
+ {
+ appendStringInfo(&cmd, " WITH (FORMAT binary)");
+ options = lappend(options, makeDefElem("format", (Node *)
makeString("binary"), -1));
+ }

Should this now be a single-line comment instead of spanning 3 lines?

======
src/test/subscription/t/014_binary.pl

5.
Everything looked OK to me, but the TAP file has only small comments
for each test step, which forces you to read everything from
top-to-bottom to understand what is going on. I felt it might be
easier to understand the tests if you add a few "bigger" comments just
to break the tests into the categories being tested. For example,
something like:


# ------------------------------------------------------
# Ensure binary mode also executes COPY in binary format
# ------------------------------------------------------

~

# --------------------------------------
# Ensure normal binary replication works
# --------------------------------------

~

# ------------------------------------------------------------------------------
# Use ALTER SUBSCRIPTION to change to text format and then back to binary format
# ------------------------------------------------------------------------------

~

# ---------------------------------------------------------------
# Test binary replication without and with send/receive functions
# ---------------------------------------------------------------

~

# ----------------------------------------------
# Test different column orders on pub/sub tables
# ----------------------------------------------

~

# -----------------------------------------------------
# Test mismatched column types with/without binary mode
# -----------------------------------------------------

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Kind Regards,
Peter Smith.
Fujitsu Australia