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Revert "Fix replay of create database records on standby"

Browse Source 
This reverts commit 49d9cfc68b.  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
This commit is contained in:
Alvaro Herrera
2022-03-29 15:36:21 +02:00
parent 6b262f353e
commit adc943b4e1
6 changed files with 1 additions and 243 deletions
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6
src/backend/access/transam/xlog.c
View File

@@ -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",

159
src/backend/access/transam/xlogutils.c
View File

@@ -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,

56
src/backend/commands/dbcommands.c
View File

@@ -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);
}

17
src/backend/commands/tablespace.c
View File

@@ -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

4
src/include/access/xlogutils.h
View File

@@ -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
{

2
src/tools/pgindent/typedefs.list
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@@ -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