Revert "Fix replay of create database records on standby"

This reverts commit 49d9cfc68bf4.  The approach taken by this patch has
problems, so we'll come up with a radically different fix.

Discussion: https://postgr.es/m/CA+TgmoYcUPL+WOJL2ZzhH=zmrhj0iOQ=iCFM0SuYqBbqZEamEg@mail.gmail.com

src/backend/access/transam/xlog.c

@@ -8255,12 +8255,6 @@ CheckRecoveryConsistency(void)
 		 */
 		XLogCheckInvalidPages();
 
-		/*
-		 * Check if the XLOG sequence contained any unresolved references to
-		 * missing directories.
-		 */
-		XLogCheckMissingDirs();
-
 		reachedConsistency = true;
 		ereport(LOG,
 				(errmsg("consistent recovery state reached at %X/%X",

src/backend/access/transam/xlogutils.c

@@ -34,164 +34,6 @@
 /* GUC variable */
 bool		ignore_invalid_pages = false;
 
-
-/*
- * If a create database WAL record is being replayed more than once during
- * crash recovery on a standby, it is possible that either the tablespace
- * directory or the template database directory is missing.  This happens when
- * the directories are removed by replay of subsequent drop records.  Note
- * that this problem happens only on standby and not on master.  On master, a
- * checkpoint is created at the end of create database operation. On standby,
- * however, such a strategy (creating restart points during replay) is not
- * viable because it will slow down WAL replay.
- *
- * The alternative is to track references to each missing directory
- * encountered when performing crash recovery in the following hash table.
- * Similar to invalid page table above, the expectation is that each missing
- * directory entry should be matched with a drop database or drop tablespace
- * WAL record by the end of crash recovery.
- */
-typedef struct xl_missing_dir_key
-{
-	Oid			spcNode;
-	Oid			dbNode;
-} xl_missing_dir_key;
-
-typedef struct xl_missing_dir
-{
-	xl_missing_dir_key key;
-	char		path[MAXPGPATH];
-} xl_missing_dir;
-
-static HTAB *missing_dir_tab = NULL;
-
-
-/*
- * Keep track of a directory that wasn't found while replaying database
- * creation records.  These should match up with tablespace removal records
- * later in the WAL stream; we verify that before reaching consistency.
- */
-void
-XLogRememberMissingDir(Oid spcNode, Oid dbNode, char *path)
-{
-	xl_missing_dir_key key;
-	bool		found;
-	xl_missing_dir *entry;
-
-	/*
-	 * Database OID may be invalid but tablespace OID must be valid.  If
-	 * dbNode is InvalidOid, we are logging a missing tablespace directory,
-	 * otherwise we are logging a missing database directory.
-	 */
-	Assert(OidIsValid(spcNode));
-
-	if (missing_dir_tab == NULL)
-	{
-		/* create hash table when first needed */
-		HASHCTL		ctl;
-
-		memset(&ctl, 0, sizeof(ctl));
-		ctl.keysize = sizeof(xl_missing_dir_key);
-		ctl.entrysize = sizeof(xl_missing_dir);
-
-		missing_dir_tab = hash_create("XLOG missing directory table",
-									  100,
-									  &ctl,
-									  HASH_ELEM | HASH_BLOBS);
-	}
-
-	key.spcNode = spcNode;
-	key.dbNode = dbNode;
-
-	entry = hash_search(missing_dir_tab, &key, HASH_ENTER, &found);
-
-	if (found)
-	{
-		if (dbNode == InvalidOid)
-			elog(DEBUG1, "missing directory %s (tablespace %u) already exists: %s",
-				 path, spcNode, entry->path);
-		else
-			elog(DEBUG1, "missing directory %s (tablespace %u database %u) already exists: %s",
-				 path, spcNode, dbNode, entry->path);
-	}
-	else
-	{
-		strlcpy(entry->path, path, sizeof(entry->path));
-		if (dbNode == InvalidOid)
-			elog(DEBUG1, "logged missing dir %s (tablespace %u)",
-				 path, spcNode);
-		else
-			elog(DEBUG1, "logged missing dir %s (tablespace %u database %u)",
-				 path, spcNode, dbNode);
-	}
-}
-
-/*
- * Remove an entry from the list of directories not found.  This is to be done
- * when the matching tablespace removal WAL record is found.
- */
-void
-XLogForgetMissingDir(Oid spcNode, Oid dbNode)
-{
-	xl_missing_dir_key key;
-
-	key.spcNode = spcNode;
-	key.dbNode = dbNode;
-
-	/* Database OID may be invalid but tablespace OID must be valid. */
-	Assert(OidIsValid(spcNode));
-
-	if (missing_dir_tab == NULL)
-		return;
-
-	if (hash_search(missing_dir_tab, &key, HASH_REMOVE, NULL) != NULL)
-	{
-		if (dbNode == InvalidOid)
-		{
-			elog(DEBUG2, "forgot missing dir (tablespace %u)", spcNode);
-		}
-		else
-		{
-			char	   *path = GetDatabasePath(dbNode, spcNode);
-
-			elog(DEBUG2, "forgot missing dir %s (tablespace %u database %u)",
-				 path, spcNode, dbNode);
-			pfree(path);
-		}
-	}
-}
-
-/*
- * This is called at the end of crash recovery, before entering archive
- * recovery on a standby.  PANIC if the hash table is not empty.
- */
-void
-XLogCheckMissingDirs(void)
-{
-	HASH_SEQ_STATUS status;
-	xl_missing_dir *hentry;
-	bool		foundone = false;
-
-	if (missing_dir_tab == NULL)
-		return;					/* nothing to do */
-
-	hash_seq_init(&status, missing_dir_tab);
-
-	while ((hentry = (xl_missing_dir *) hash_seq_search(&status)) != NULL)
-	{
-		elog(WARNING, "missing directory \"%s\" tablespace %u database %u",
-			 hentry->path, hentry->key.spcNode, hentry->key.dbNode);
-		foundone = true;
-	}
-
-	if (foundone)
-		elog(PANIC, "WAL contains references to missing directories");
-
-	hash_destroy(missing_dir_tab);
-	missing_dir_tab = NULL;
-}
-
-
 /*
  * During XLOG replay, we may see XLOG records for incremental updates of
  * pages that no longer exist, because their relation was later dropped or
@@ -217,6 +59,7 @@ typedef struct xl_invalid_page
 
 static HTAB *invalid_page_tab = NULL;
 
+
 /* Report a reference to an invalid page */
 static void
 report_invalid_page(int elevel, RelFileNode node, ForkNumber forkno,

src/backend/commands/dbcommands.c

@@ -2185,9 +2185,7 @@ dbase_redo(XLogReaderState *record)
 		xl_dbase_create_rec *xlrec = (xl_dbase_create_rec *) XLogRecGetData(record);
 		char	   *src_path;
 		char	   *dst_path;
-		char	   *parent_path;
 		struct stat st;
-		bool		skip = false;
 
 		src_path = GetDatabasePath(xlrec->src_db_id, xlrec->src_tablespace_id);
 		dst_path = GetDatabasePath(xlrec->db_id, xlrec->tablespace_id);
@@ -2205,56 +2203,6 @@ dbase_redo(XLogReaderState *record)
 						(errmsg("some useless files may be left behind in old database directory \"%s\"",
 								dst_path)));
 		}
-		else if (!reachedConsistency)
-		{
-			/*
-			 * It is possible that a drop tablespace record appearing later in
-			 * WAL has already been replayed -- in other words, that we are
-			 * replaying the database creation record a second time with no
-			 * intervening checkpoint.  In that case, the tablespace directory
-			 * has already been removed and the create database operation
-			 * cannot be replayed.  Skip the replay itself, but remember the
-			 * fact that the tablespace directory is missing, to be matched
-			 * with the expected tablespace drop record later.
-			 */
-			parent_path = pstrdup(dst_path);
-			get_parent_directory(parent_path);
-			if (!(stat(parent_path, &st) == 0 && S_ISDIR(st.st_mode)))
-			{
-				XLogRememberMissingDir(xlrec->tablespace_id, InvalidOid, parent_path);
-				skip = true;
-				ereport(WARNING,
-						(errmsg("skipping replay of database creation WAL record"),
-						 errdetail("The target tablespace \"%s\" directory was not found.",
-								   parent_path),
-						 errhint("A future WAL record that removes the directory before reaching consistent mode is expected.")));
-			}
-			pfree(parent_path);
-		}
-
-		/*
-		 * If the source directory is missing, skip the copy and make a note of
-		 * it for later.
-		 *
-		 * One possible reason for this is that the template database used for
-		 * creating this database may have been dropped, as noted above.
-		 * Moving a database from one tablespace may also be a partner in the
-		 * crime.
-		 */
-		if (!(stat(src_path, &st) == 0 && S_ISDIR(st.st_mode)) &&
-			!reachedConsistency)
-		{
-			XLogRememberMissingDir(xlrec->src_tablespace_id, xlrec->src_db_id, src_path);
-			skip = true;
-			ereport(WARNING,
-					(errmsg("skipping replay of database creation WAL record"),
-					 errdetail("The source database directory \"%s\" was not found.",
-							   src_path),
-					 errhint("A future WAL record that removes the directory before reaching consistent mode is expected.")));
-		}
-
-		if (skip)
-			return;
 
 		/*
 		 * Force dirty buffers out to disk, to ensure source database is
@@ -2312,10 +2260,6 @@ dbase_redo(XLogReaderState *record)
 				ereport(WARNING,
 						(errmsg("some useless files may be left behind in old database directory \"%s\"",
 								dst_path)));
-
-			if (!reachedConsistency)
-				XLogForgetMissingDir(xlrec->tablespace_ids[i], xlrec->db_id);
-
 			pfree(dst_path);
 		}
 

src/backend/commands/tablespace.c

@@ -58,7 +58,6 @@
 #include "access/xact.h"
 #include "access/xlog.h"
 #include "access/xloginsert.h"
-#include "access/xlogutils.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
 #include "catalog/indexing.h"
@@ -1530,22 +1529,6 @@ tblspc_redo(XLogReaderState *record)
 	{
 		xl_tblspc_drop_rec *xlrec = (xl_tblspc_drop_rec *) XLogRecGetData(record);
 
-		if (!reachedConsistency)
-			XLogForgetMissingDir(xlrec->ts_id, InvalidOid);
-
-		/*
-		 * Before we remove the tablespace directory, update minimum recovery
-		 * point to cover this WAL record. Once the tablespace is removed,
-		 * there's no going back.  This manually enforces the WAL-first rule.
-		 * Doing this before the removal means that if the removal fails for
-		 * some reason, the directory is left alone and needs to be manually
-		 * removed.  Alternatively we could update the minimum recovery point
-		 * after removal, but that would leave a small window where the
-		 * WAL-first rule could be violated.
-		 */
-		if (!reachedConsistency)
-			XLogFlush(record->EndRecPtr);
-
 		/*
 		 * If we issued a WAL record for a drop tablespace it implies that
 		 * there were no files in it at all when the DROP was done. That means

src/include/access/xlogutils.h

@@ -23,10 +23,6 @@ extern void XLogDropDatabase(Oid dbid);
 extern void XLogTruncateRelation(RelFileNode rnode, ForkNumber forkNum,
 								 BlockNumber nblocks);
 
-extern void XLogRememberMissingDir(Oid spcNode, Oid dbNode, char *path);
-extern void XLogForgetMissingDir(Oid spcNode, Oid dbNode);
-extern void XLogCheckMissingDirs(void);
-
 /* Result codes for XLogReadBufferForRedo[Extended] */
 typedef enum
 {

src/tools/pgindent/typedefs.list

@@ -3700,8 +3700,6 @@ xl_invalid_page
 xl_invalid_page_key
 xl_invalidations
 xl_logical_message
-xl_missing_dir_key
-xl_missing_dir
 xl_multi_insert_tuple
 xl_multixact_create
 xl_multixact_truncate