Provide an extra-float-digits setting for pg_dump / pg_dumpall

Changes made by commit 02ddd49 mean that dumps made against pre version
12 instances are no longer comparable with those made against version 12
or later instances. This makes cross-version upgrade testing fail in the
buildfarm. Experimentation has shown that the error is cured if the
dumps are made when extra_float_digits is set to 0. Hence this patch
allows for it to be explicitly set rather than relying on pg_dump's
builtin default (3 in almost all cases). This feature might have other
uses, but should not normally be used.

Discussion: https://postgr.es/m/c76f7051-8fd3-ec10-7579-1f8842305b85@2ndQuadrant.com

Author: adunstan

doc/src/sgml/ref/pg_dump.sgml

@@ -745,6 +745,17 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--extra-float-digits=<replaceable class="parameter">ndigits</replaceable></option></term>
+      <listitem>
+       <para>
+        Use the specified value of extra_float_digits when dumping
+        floating-point data, instead of the maximum available precision.
+        Routine dumps made for backup purposes should not use this option.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>--if-exists</option></term>
       <listitem>

doc/src/sgml/ref/pg_dumpall.sgml

@@ -300,6 +300,17 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--extra-float-digits=<replaceable class="parameter">ndigits</replaceable></option></term>
+      <listitem>
+       <para>
+        Use the specified value of extra_float_digits when dumping
+        floating-point data, instead of the maximum available precision.
+        Routine dumps made for backup purposes should not use this option.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>--if-exists</option></term>
       <listitem>

src/bin/pg_dump/pg_dump.c

@@ -134,6 +134,10 @@ char		g_comment_end[10];
 
 static const CatalogId nilCatalogId = {0, 0};
 
+/* override for standard extra_float_digits setting */
+static bool have_extra_float_digits = false;
+static int extra_float_digits;
+
 /*
  * Macro for producing quoted, schema-qualified name of a dumpable object.
  */
@@ -357,6 +361,7 @@ main(int argc, char **argv)
 		{"disable-triggers", no_argument, &dopt.disable_triggers, 1},
 		{"enable-row-security", no_argument, &dopt.enable_row_security, 1},
 		{"exclude-table-data", required_argument, NULL, 4},
+		{"extra-float-digits", required_argument, NULL, 8},
 		{"if-exists", no_argument, &dopt.if_exists, 1},
 		{"inserts", no_argument, &dopt.dump_inserts, 1},
 		{"lock-wait-timeout", required_argument, NULL, 2},
@@ -557,6 +562,16 @@ main(int argc, char **argv)
 				dosync = false;
 				break;
 
+			case 8:
+				have_extra_float_digits = true;
+				extra_float_digits = atoi(optarg);
+				if (extra_float_digits < -15 || extra_float_digits > 3)
+				{
+					write_msg(NULL, "extra_float_digits must be in range -15..3\n");
+					exit_nicely(1);
+				}
+				break;
+
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit_nicely(1);
@@ -965,6 +980,7 @@ help(const char *progname)
 	printf(_("  --enable-row-security        enable row security (dump only content user has\n"
 			 "                               access to)\n"));
 	printf(_("  --exclude-table-data=TABLE   do NOT dump data for the named table(s)\n"));
+	printf(_("  --extra-float-digits=NUM     override default setting for extra_float_digits\n"));
 	printf(_("  --if-exists                  use IF EXISTS when dropping objects\n"));
 	printf(_("  --inserts                    dump data as INSERT commands, rather than COPY\n"));
 	printf(_("  --load-via-partition-root    load partitions via the root table\n"));
@@ -1059,10 +1075,19 @@ setup_connection(Archive *AH, const char *dumpencoding,
 		ExecuteSqlStatement(AH, "SET INTERVALSTYLE = POSTGRES");
 
 	/*
-	 * Set extra_float_digits so that we can dump float data exactly (given
-	 * correctly implemented float I/O code, anyway)
+	 * Use an explicitly specified extra_float_digits if it has been
+	 * provided. Otherwise, set extra_float_digits so that we can dump float
+	 * data exactly (given correctly implemented float I/O code, anyway).
 	 */
-	if (AH->remoteVersion >= 90000)
+	if (have_extra_float_digits)
+	{
+		PQExpBuffer q = createPQExpBuffer();
+		appendPQExpBuffer(q, "SET extra_float_digits TO %d",
+						  extra_float_digits);
+		ExecuteSqlStatement(AH, q->data);
+		destroyPQExpBuffer(q);
+	}
+	else if (AH->remoteVersion >= 90000)
 		ExecuteSqlStatement(AH, "SET extra_float_digits TO 3");
 	else
 		ExecuteSqlStatement(AH, "SET extra_float_digits TO 2");

src/bin/pg_dump/pg_dumpall.c

@@ -123,6 +123,7 @@ main(int argc, char *argv[])
 		{"column-inserts", no_argument, &column_inserts, 1},
 		{"disable-dollar-quoting", no_argument, &disable_dollar_quoting, 1},
 		{"disable-triggers", no_argument, &disable_triggers, 1},
+		{"extra-float-digits", required_argument, NULL, 5},
 		{"if-exists", no_argument, &if_exists, 1},
 		{"inserts", no_argument, &inserts, 1},
 		{"lock-wait-timeout", required_argument, NULL, 2},
@@ -318,6 +319,11 @@ main(int argc, char *argv[])
 				appendPQExpBufferStr(pgdumpopts, " --no-sync");
 				break;
 
+			case 5:
+				appendPQExpBufferStr(pgdumpopts, " --extra-float-digits ");
+				appendShellString(pgdumpopts, optarg);
+				break;
+
 			default:
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 				exit_nicely(1);
@@ -614,6 +620,7 @@ help(void)
 	printf(_("  --column-inserts             dump data as INSERT commands with column names\n"));
 	printf(_("  --disable-dollar-quoting     disable dollar quoting, use SQL standard quoting\n"));
 	printf(_("  --disable-triggers           disable triggers during data-only restore\n"));
+	printf(_("  --extra-float-digits=NUM     override default setting for extra_float_digits\n"));
 	printf(_("  --if-exists                  use IF EXISTS when dropping objects\n"));
 	printf(_("  --inserts                    dump data as INSERT commands, rather than COPY\n"));
 	printf(_("  --load-via-partition-root    load partitions via the root table\n"));