Add hint when checksum delta is enabled after a timeline switch.

This warning is normal when restoring a backup or promoting a standby so add a hint to make that clear.

doc/xml/release.xml

@@ -30,6 +30,16 @@
 
                         <p>Improve error when <br-option>pg1-path</br-option> option missing for <cmd>archive-get</cmd> command.</p>
                     </release-item>
+
+                    <release-item>
+                        <release-item-contributor-list>
+                            <release-item-contributor id="david.steele"/>
+                            <release-item-reviewer id="matt.bunter"/>
+                            <release-item-reviewer id="cynthia.shang"/>
+                        </release-item-contributor-list>
+
+                        <p>Add hint when checksum delta is enabled after a timeline switch.</p>
+                    </release-item>
                 </release-improvement-list>
 
                 <release-development-list>
@@ -8558,6 +8568,11 @@
             <contributor-id type="github">mnullmei</contributor-id>
         </contributor>
 
+        <contributor id="matt.bunter">
+            <contributor-name-display>Matt Bunter</contributor-name-display>
+            <contributor-id type="github">mattbunter</contributor-id>
+        </contributor>
+
         <contributor id="matt.kunkel">
             <contributor-name-display>Matt Kunkel</contributor-name-display>
             <contributor-id type="github">mtkunkel</contributor-id>

src/info/manifest.c

@@ -1120,7 +1120,8 @@ manifestBuildIncr(Manifest *this, const Manifest *manifestPrior, BackupType type
             !strEq(strSubN(archiveStart, 0, 8), strSubN(manifestData(manifestPrior)->archiveStop, 0, 8)))
         {
             LOG_WARN_FMT(
-                "a timeline switch has occurred since the %s backup, enabling delta checksum",
+                "a timeline switch has occurred since the %s backup, enabling delta checksum\n"
+                "HINT: this is normal after restoring from backup or promoting a standby.",
                 strPtr(manifestData(manifestPrior)->backupLabel));
 
             this->data.backupOptionDelta = BOOL_TRUE_VAR;

test/src/module/command/backupTest.c

@@ -2457,6 +2457,7 @@ testRun(void)
                 "P00   INFO: execute non-exclusive pg_start_backup(): backup begins after the next regular checkpoint completes\n"
                 "P00   INFO: backup start archive = 0000002C05DB8EB000000000, lsn = 5db8eb0/0\n"
                 "P00   WARN: a timeline switch has occurred since the 20191027-181320F backup, enabling delta checksum\n"
+                "            HINT: this is normal after restoring from backup or promoting a standby.\n"
                 "P01 DETAIL: match file from prior backup {[path]}/pg1/global/pg_control (8KB, [PCT]) checksum [SHA1]\n"
                 "P01 DETAIL: match file from prior backup {[path]}/pg1/postgresql.conf (11B, [PCT]) checksum [SHA1]\n"
                 "P01 DETAIL: match file from prior backup {[path]}/pg1/PG_VERSION (2B, [PCT]) checksum [SHA1]\n"

test/src/module/info/manifestTest.c

@@ -1483,7 +1483,9 @@ testRun(void)
         TEST_RESULT_VOID(
             manifestBuildIncr(manifest, manifestPrior, backupTypeIncr, STRDEF("000000040000000400000004")), "incremental manifest");
 
-        TEST_RESULT_LOG("P00   WARN: a timeline switch has occurred since the 20190101-010101F backup, enabling delta checksum");
+        TEST_RESULT_LOG(
+            "P00   WARN: a timeline switch has occurred since the 20190101-010101F backup, enabling delta checksum\n"
+            "            HINT: this is normal after restoring from backup or promoting a standby.");
 
         TEST_RESULT_BOOL(varBool(manifest->data.backupOptionDelta), true, "check delta is enabled");