Revert pg_relation_check_pages()

This reverts the following set of commits, following complaints about
the lack of portability of the central part of the code in bufmgr.c as
well as the use of partition mapping locks during page reads:
c780a7a
f2b8839
b787d4c
ce7f772
60a51c6

Per discussion with Andres Freund, Robert Haas and myself.

Bump catalog version.

Discussion: https://postgr.es/m/20201029181729.2nrub47u7yqncsv7@alap3.anarazel.de

Author: michaelpq

doc/src/sgml/func.sgml

@@ -26171,62 +26171,6 @@ SELECT convert_from(pg_read_binary_file('file_in_utf8.txt'), 'UTF8');
 
   </sect2>
 
-  <sect2 id="functions-data-sanity">
-   <title>Data Sanity Functions</title>
-
-   <para>
-    The functions shown in <xref linkend="functions-data-sanity-table"/>
-    provide ways to check the sanity of data files in the cluster.
-   </para>
-
-   <table id="functions-data-sanity-table">
-    <title>Data Sanity Functions</title>
-    <tgroup cols="1">
-     <thead>
-      <row>
-       <entry role="func_table_entry"><para role="func_signature">
-        Function
-       </para>
-       <para>
-        Description
-       </para></entry>
-      </row>
-     </thead>
-
-     <tbody>
-      <row>
-       <entry role="func_table_entry"><para role="func_signature">
-        <indexterm>
-         <primary>pg_relation_check_pages</primary>
-        </indexterm>
-        <function>pg_relation_check_pages</function> ( <parameter>relation</parameter> <type>regclass</type> [, <parameter>fork</parameter> <type>text</type> ] )
-        <returnvalue>setof record</returnvalue>
-        ( <parameter>path</parameter> <type>text</type>,
-        <parameter>failed_block_num</parameter> <type>bigint</type> )
-       </para>
-       <para>
-        Checks the pages of the specified relation to see if they are valid
-        enough to safely be loaded into the server's shared buffers.  If
-        given, <parameter>fork</parameter> specifies that only the pages of
-        the given fork are to be verified.  <parameter>fork</parameter> can
-        be <literal>main</literal> for the main data
-        fork, <literal>fsm</literal> for the free space
-        map, <literal>vm</literal> for the visibility map,
-        or <literal>init</literal> for the initialization fork.  The
-        default of <literal>NULL</literal> means that all forks of the
-        relation should be checked.  The function returns a list of block
-        numbers that appear corrupted along with the path names of their
-        files.  Use of this function is restricted to superusers by
-        default, but access may be granted to others
-        using <command>GRANT</command>.
-       </para></entry>
-      </row>
-     </tbody>
-    </tgroup>
-   </table>
-
-  </sect2>
-
   </sect1>
 
   <sect1 id="functions-trigger">

src/backend/catalog/system_views.sql

@@ -1303,14 +1303,6 @@ LANGUAGE INTERNAL
 STRICT VOLATILE
 AS 'pg_create_logical_replication_slot';
 
-CREATE OR REPLACE FUNCTION pg_relation_check_pages(
-    IN relation regclass, IN fork text DEFAULT NULL,
-    OUT path text, OUT failed_block_num bigint)
-RETURNS SETOF record
-LANGUAGE internal
-VOLATILE PARALLEL RESTRICTED
-AS 'pg_relation_check_pages';
-
 CREATE OR REPLACE FUNCTION
   make_interval(years int4 DEFAULT 0, months int4 DEFAULT 0, weeks int4 DEFAULT 0,
                 days int4 DEFAULT 0, hours int4 DEFAULT 0, mins int4 DEFAULT 0,
@@ -1455,7 +1447,6 @@ AS 'unicode_is_normalized';
 -- can later change who can access these functions, or leave them as only
 -- available to superuser / cluster owner, if they choose.
 --
-REVOKE EXECUTE ON FUNCTION pg_relation_check_pages(regclass, text) FROM public;
 REVOKE EXECUTE ON FUNCTION pg_start_backup(text, boolean, boolean) FROM public;
 REVOKE EXECUTE ON FUNCTION pg_stop_backup() FROM public;
 REVOKE EXECUTE ON FUNCTION pg_stop_backup(boolean, boolean) FROM public;

src/backend/storage/buffer/bufmgr.c

@@ -4585,95 +4585,3 @@ TestForOldSnapshot_impl(Snapshot snapshot, Relation relation)
 				(errcode(ERRCODE_SNAPSHOT_TOO_OLD),
 				 errmsg("snapshot too old")));
 }
-
-
-/*
- * CheckBuffer
- *
- * Check the state of a buffer without loading it into the shared buffers. To
- * avoid torn pages and possible false positives when reading data, a shared
- * LWLock is taken on the target buffer pool partition mapping, and we check
- * if the page is in shared buffers or not.  An I/O lock is taken on the block
- * to prevent any concurrent activity from happening.
- *
- * If the page is found as dirty in the shared buffers, it is ignored as
- * it will be flushed to disk either before the end of the next checkpoint
- * or during recovery in the event of an unsafe shutdown.
- *
- * If the page is found in the shared buffers but is not dirty, we still
- * check the state of its data on disk, as it could be possible that the
- * page stayed in shared buffers for a rather long time while the on-disk
- * data got corrupted.
- *
- * If the page is not found in shared buffers, the block is read from disk
- * while holding the buffer pool partition mapping LWLock.
- *
- * The page data is stored in a private memory area local to this function
- * while running the checks.
- */
-bool
-CheckBuffer(SMgrRelation smgr, ForkNumber forknum, BlockNumber blkno)
-{
-	char		buffer[BLCKSZ];
-	BufferTag	buf_tag;		/* identity of requested block */
-	uint32		buf_hash;		/* hash value for buf_tag */
-	LWLock	   *partLock;		/* buffer partition lock for the buffer */
-	BufferDesc *bufdesc;
-	int			buf_id;
-
-	Assert(smgrexists(smgr, forknum));
-
-	/* create a tag so we can look after the buffer */
-	INIT_BUFFERTAG(buf_tag, smgr->smgr_rnode.node, forknum, blkno);
-
-	/* determine its hash code and partition lock ID */
-	buf_hash = BufTableHashCode(&buf_tag);
-	partLock = BufMappingPartitionLock(buf_hash);
-
-	/* see if the block is in the buffer pool or not */
-	LWLockAcquire(partLock, LW_SHARED);
-	buf_id = BufTableLookup(&buf_tag, buf_hash);
-	if (buf_id >= 0)
-	{
-		uint32		buf_state;
-
-		/*
-		 * Found it.  Now, retrieve its state to know what to do with it, and
-		 * release the pin immediately.  We do so to limit overhead as much as
-		 * possible.  We keep the shared LWLock on the target buffer mapping
-		 * partition for now, so this buffer cannot be evicted, and we acquire
-		 * an I/O Lock on the buffer as we may need to read its contents from
-		 * disk.
-		 */
-		bufdesc = GetBufferDescriptor(buf_id);
-
-		LWLockAcquire(BufferDescriptorGetIOLock(bufdesc), LW_SHARED);
-		buf_state = LockBufHdr(bufdesc);
-		UnlockBufHdr(bufdesc, buf_state);
-
-		/* If the page is dirty or invalid, skip it */
-		if ((buf_state & BM_DIRTY) != 0 || (buf_state & BM_TAG_VALID) == 0)
-		{
-			LWLockRelease(BufferDescriptorGetIOLock(bufdesc));
-			LWLockRelease(partLock);
-			return true;
-		}
-
-		/* Read the buffer from disk, with the I/O lock still held */
-		smgrread(smgr, forknum, blkno, buffer);
-		LWLockRelease(BufferDescriptorGetIOLock(bufdesc));
-	}
-	else
-	{
-		/*
-		 * Simply read the buffer.  There's no risk of modification on it as
-		 * we are holding the buffer pool partition mapping lock.
-		 */
-		smgrread(smgr, forknum, blkno, buffer);
-	}
-
-	/* buffer lookup done, so now do its check */
-	LWLockRelease(partLock);
-
-	return PageIsVerifiedExtended(buffer, blkno, PIV_REPORT_STAT);
-}

src/backend/utils/adt/Makefile

@@ -69,7 +69,6 @@ OBJS = \
 	oid.o \
 	oracle_compat.o \
 	orderedsetaggs.o \
-	pagefuncs.o \
 	partitionfuncs.o \
 	pg_locale.o \
 	pg_lsn.o \