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|
/*-------------------------------------------------------------------------
*
* relmapper.c
* Catalog-to-filenode mapping
*
* For most tables, the physical file underlying the table is specified by
* pg_class.relfilenode. However, that obviously won't work for pg_class
* itself, nor for the other "nailed" catalogs for which we have to be able
* to set up working Relation entries without access to pg_class. It also
* does not work for shared catalogs, since there is no practical way to
* update other databases' pg_class entries when relocating a shared catalog.
* Therefore, for these special catalogs (henceforth referred to as "mapped
* catalogs") we rely on a separately maintained file that shows the mapping
* from catalog OIDs to filenode numbers. Each database has a map file for
* its local mapped catalogs, and there is a separate map file for shared
* catalogs. Mapped catalogs have zero in their pg_class.relfilenode entries.
*
* Relocation of a normal table is committed (ie, the new physical file becomes
* authoritative) when the pg_class row update commits. For mapped catalogs,
* the act of updating the map file is effectively commit of the relocation.
* We postpone the file update till just before commit of the transaction
* doing the rewrite, but there is necessarily a window between. Therefore
* mapped catalogs can only be relocated by operations such as VACUUM FULL
* and CLUSTER, which make no transactionally-significant changes: it must be
* safe for the new file to replace the old, even if the transaction itself
* aborts. An important factor here is that the indexes and toast table of
* a mapped catalog must also be mapped, so that the rewrites/relocations of
* all these files commit in a single map file update rather than being tied
* to transaction commit.
*
* Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/utils/cache/relmapper.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include "access/xact.h"
#include "access/xlog.h"
#include "access/xloginsert.h"
#include "catalog/catalog.h"
#include "catalog/pg_tablespace.h"
#include "catalog/storage.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/fd.h"
#include "storage/lwlock.h"
#include "utils/inval.h"
#include "utils/relmapper.h"
/*
* The map file is critical data: we have no automatic method for recovering
* from loss or corruption of it. We use a CRC so that we can detect
* corruption. To minimize the risk of failed updates, the map file should
* be kept to no more than one standard-size disk sector (ie 512 bytes),
* and we use overwrite-in-place rather than playing renaming games.
* The struct layout below is designed to occupy exactly 512 bytes, which
* might make filesystem updates a bit more efficient.
*
* Entries in the mappings[] array are in no particular order. We could
* speed searching by insisting on OID order, but it really shouldn't be
* worth the trouble given the intended size of the mapping sets.
*/
#define RELMAPPER_FILENAME "pg_filenode.map"
#define RELMAPPER_FILEMAGIC 0x592717 /* version ID value */
#define MAX_MAPPINGS 62 /* 62 * 8 + 16 = 512 */
typedef struct RelMapping
{
Oid mapoid; /* OID of a catalog */
Oid mapfilenode; /* its filenode number */
} RelMapping;
typedef struct RelMapFile
{
int32 magic; /* always RELMAPPER_FILEMAGIC */
int32 num_mappings; /* number of valid RelMapping entries */
RelMapping mappings[MAX_MAPPINGS];
pg_crc32c crc; /* CRC of all above */
int32 pad; /* to make the struct size be 512 exactly */
} RelMapFile;
/*
* The currently known contents of the shared map file and our database's
* local map file are stored here. These can be reloaded from disk
* immediately whenever we receive an update sinval message.
*/
static RelMapFile shared_map;
static RelMapFile local_map;
/*
* We use the same RelMapFile data structure to track uncommitted local
* changes in the mappings (but note the magic and crc fields are not made
* valid in these variables). Currently, map updates are not allowed within
* subtransactions, so one set of transaction-level changes is sufficient.
*
* The active_xxx variables contain updates that are valid in our transaction
* and should be honored by RelationMapOidToFilenode. The pending_xxx
* variables contain updates we have been told about that aren't active yet;
* they will become active at the next CommandCounterIncrement. This setup
* lets map updates act similarly to updates of pg_class rows, ie, they
* become visible only at the next CommandCounterIncrement boundary.
*/
static RelMapFile active_shared_updates;
static RelMapFile active_local_updates;
static RelMapFile pending_shared_updates;
static RelMapFile pending_local_updates;
/* non-export function prototypes */
static void apply_map_update(RelMapFile *map, Oid relationId, Oid fileNode,
bool add_okay);
static void merge_map_updates(RelMapFile *map, const RelMapFile *updates,
bool add_okay);
static void load_relmap_file(bool shared);
static void write_relmap_file(bool shared, RelMapFile *newmap,
bool write_wal, bool send_sinval, bool preserve_files,
Oid dbid, Oid tsid, const char *dbpath);
static void perform_relmap_update(bool shared, const RelMapFile *updates);
/*
* RelationMapOidToFilenode
*
* The raison d' etre ... given a relation OID, look up its filenode.
*
* Although shared and local relation OIDs should never overlap, the caller
* always knows which we need --- so pass that information to avoid useless
* searching.
*
* Returns InvalidOid if the OID is not known (which should never happen,
* but the caller is in a better position to report a meaningful error).
*/
Oid
RelationMapOidToFilenode(Oid relationId, bool shared)
{
const RelMapFile *map;
int32 i;
/* If there are active updates, believe those over the main maps */
if (shared)
{
map = &active_shared_updates;
for (i = 0; i < map->num_mappings; i++)
{
if (relationId == map->mappings[i].mapoid)
return map->mappings[i].mapfilenode;
}
map = &shared_map;
for (i = 0; i < map->num_mappings; i++)
{
if (relationId == map->mappings[i].mapoid)
return map->mappings[i].mapfilenode;
}
}
else
{
map = &active_local_updates;
for (i = 0; i < map->num_mappings; i++)
{
if (relationId == map->mappings[i].mapoid)
return map->mappings[i].mapfilenode;
}
map = &local_map;
for (i = 0; i < map->num_mappings; i++)
{
if (relationId == map->mappings[i].mapoid)
return map->mappings[i].mapfilenode;
}
}
return InvalidOid;
}
/*
* RelationMapFilenodeToOid
*
* Do the reverse of the normal direction of mapping done in
* RelationMapOidToFilenode.
*
* This is not supposed to be used during normal running but rather for
* information purposes when looking at the filesystem or xlog.
*
* Returns InvalidOid if the OID is not known; this can easily happen if the
* relfilenode doesn't pertain to a mapped relation.
*/
Oid
RelationMapFilenodeToOid(Oid filenode, bool shared)
{
const RelMapFile *map;
int32 i;
/* If there are active updates, believe those over the main maps */
if (shared)
{
map = &active_shared_updates;
for (i = 0; i < map->num_mappings; i++)
{
if (filenode == map->mappings[i].mapfilenode)
return map->mappings[i].mapoid;
}
map = &shared_map;
for (i = 0; i < map->num_mappings; i++)
{
if (filenode == map->mappings[i].mapfilenode)
return map->mappings[i].mapoid;
}
}
else
{
map = &active_local_updates;
for (i = 0; i < map->num_mappings; i++)
{
if (filenode == map->mappings[i].mapfilenode)
return map->mappings[i].mapoid;
}
map = &local_map;
for (i = 0; i < map->num_mappings; i++)
{
if (filenode == map->mappings[i].mapfilenode)
return map->mappings[i].mapoid;
}
}
return InvalidOid;
}
/*
* RelationMapUpdateMap
*
* Install a new relfilenode mapping for the specified relation.
*
* If immediate is true (or we're bootstrapping), the mapping is activated
* immediately. Otherwise it is made pending until CommandCounterIncrement.
*/
void
RelationMapUpdateMap(Oid relationId, Oid fileNode, bool shared,
bool immediate)
{
RelMapFile *map;
if (IsBootstrapProcessingMode())
{
/*
* In bootstrap mode, the mapping gets installed in permanent map.
*/
if (shared)
map = &shared_map;
else
map = &local_map;
}
else
{
/*
* We don't currently support map changes within subtransactions. This
* could be done with more bookkeeping infrastructure, but it doesn't
* presently seem worth it.
*/
if (GetCurrentTransactionNestLevel() > 1)
elog(ERROR, "cannot change relation mapping within subtransaction");
if (immediate)
{
/* Make it active, but only locally */
if (shared)
map = &active_shared_updates;
else
map = &active_local_updates;
}
else
{
/* Make it pending */
if (shared)
map = &pending_shared_updates;
else
map = &pending_local_updates;
}
}
apply_map_update(map, relationId, fileNode, true);
}
/*
* apply_map_update
*
* Insert a new mapping into the given map variable, replacing any existing
* mapping for the same relation.
*
* In some cases the caller knows there must be an existing mapping; pass
* add_okay = false to draw an error if not.
*/
static void
apply_map_update(RelMapFile *map, Oid relationId, Oid fileNode, bool add_okay)
{
int32 i;
/* Replace any existing mapping */
for (i = 0; i < map->num_mappings; i++)
{
if (relationId == map->mappings[i].mapoid)
{
map->mappings[i].mapfilenode = fileNode;
return;
}
}
/* Nope, need to add a new mapping */
if (!add_okay)
elog(ERROR, "attempt to apply a mapping to unmapped relation %u",
relationId);
if (map->num_mappings >= MAX_MAPPINGS)
elog(ERROR, "ran out of space in relation map");
map->mappings[map->num_mappings].mapoid = relationId;
map->mappings[map->num_mappings].mapfilenode = fileNode;
map->num_mappings++;
}
/*
* merge_map_updates
*
* Merge all the updates in the given pending-update map into the target map.
* This is just a bulk form of apply_map_update.
*/
static void
merge_map_updates(RelMapFile *map, const RelMapFile *updates, bool add_okay)
{
int32 i;
for (i = 0; i < updates->num_mappings; i++)
{
apply_map_update(map,
updates->mappings[i].mapoid,
updates->mappings[i].mapfilenode,
add_okay);
}
}
/*
* RelationMapRemoveMapping
*
* Remove a relation's entry in the map. This is only allowed for "active"
* (but not committed) local mappings. We need it so we can back out the
* entry for the transient target file when doing VACUUM FULL/CLUSTER on
* a mapped relation.
*/
void
RelationMapRemoveMapping(Oid relationId)
{
RelMapFile *map = &active_local_updates;
int32 i;
for (i = 0; i < map->num_mappings; i++)
{
if (relationId == map->mappings[i].mapoid)
{
/* Found it, collapse it out */
map->mappings[i] = map->mappings[map->num_mappings - 1];
map->num_mappings--;
return;
}
}
elog(ERROR, "could not find temporary mapping for relation %u",
relationId);
}
/*
* RelationMapInvalidate
*
* This routine is invoked for SI cache flush messages. We must re-read
* the indicated map file. However, we might receive a SI message in a
* process that hasn't yet, and might never, load the mapping files;
* for example the autovacuum launcher, which *must not* try to read
* a local map since it is attached to no particular database.
* So, re-read only if the map is valid now.
*/
void
RelationMapInvalidate(bool shared)
{
if (shared)
{
if (shared_map.magic == RELMAPPER_FILEMAGIC)
load_relmap_file(true);
}
else
{
if (local_map.magic == RELMAPPER_FILEMAGIC)
load_relmap_file(false);
}
}
/*
* RelationMapInvalidateAll
*
* Reload all map files. This is used to recover from SI message buffer
* overflow: we can't be sure if we missed an inval message.
* Again, reload only currently-valid maps.
*/
void
RelationMapInvalidateAll(void)
{
if (shared_map.magic == RELMAPPER_FILEMAGIC)
load_relmap_file(true);
if (local_map.magic == RELMAPPER_FILEMAGIC)
load_relmap_file(false);
}
/*
* AtCCI_RelationMap
*
* Activate any "pending" relation map updates at CommandCounterIncrement time.
*/
void
AtCCI_RelationMap(void)
{
if (pending_shared_updates.num_mappings != 0)
{
merge_map_updates(&active_shared_updates,
&pending_shared_updates,
true);
pending_shared_updates.num_mappings = 0;
}
if (pending_local_updates.num_mappings != 0)
{
merge_map_updates(&active_local_updates,
&pending_local_updates,
true);
pending_local_updates.num_mappings = 0;
}
}
/*
* AtEOXact_RelationMap
*
* Handle relation mapping at main-transaction commit or abort.
*
* During commit, this must be called as late as possible before the actual
* transaction commit, so as to minimize the window where the transaction
* could still roll back after committing map changes. Although nothing
* critically bad happens in such a case, we still would prefer that it
* not happen, since we'd possibly be losing useful updates to the relations'
* pg_class row(s).
*
* During abort, we just have to throw away any pending map changes.
* Normal post-abort cleanup will take care of fixing relcache entries.
*/
void
AtEOXact_RelationMap(bool isCommit)
{
if (isCommit)
{
/*
* We should not get here with any "pending" updates. (We could
* logically choose to treat such as committed, but in the current
* code this should never happen.)
*/
Assert(pending_shared_updates.num_mappings == 0);
Assert(pending_local_updates.num_mappings == 0);
/*
* Write any active updates to the actual map files, then reset them.
*/
if (active_shared_updates.num_mappings != 0)
{
perform_relmap_update(true, &active_shared_updates);
active_shared_updates.num_mappings = 0;
}
if (active_local_updates.num_mappings != 0)
{
perform_relmap_update(false, &active_local_updates);
active_local_updates.num_mappings = 0;
}
}
else
{
/* Abort --- drop all local and pending updates */
active_shared_updates.num_mappings = 0;
active_local_updates.num_mappings = 0;
pending_shared_updates.num_mappings = 0;
pending_local_updates.num_mappings = 0;
}
}
/*
* AtPrepare_RelationMap
*
* Handle relation mapping at PREPARE.
*
* Currently, we don't support preparing any transaction that changes the map.
*/
void
AtPrepare_RelationMap(void)
{
if (active_shared_updates.num_mappings != 0 ||
active_local_updates.num_mappings != 0 ||
pending_shared_updates.num_mappings != 0 ||
pending_local_updates.num_mappings != 0)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot PREPARE a transaction that modified relation mapping")));
}
/*
* CheckPointRelationMap
*
* This is called during a checkpoint. It must ensure that any relation map
* updates that were WAL-logged before the start of the checkpoint are
* securely flushed to disk and will not need to be replayed later. This
* seems unlikely to be a performance-critical issue, so we use a simple
* method: we just take and release the RelationMappingLock. This ensures
* that any already-logged map update is complete, because write_relmap_file
* will fsync the map file before the lock is released.
*/
void
CheckPointRelationMap(void)
{
LWLockAcquire(RelationMappingLock, LW_SHARED);
LWLockRelease(RelationMappingLock);
}
/*
* RelationMapFinishBootstrap
*
* Write out the initial relation mapping files at the completion of
* bootstrap. All the mapped files should have been made known to us
* via RelationMapUpdateMap calls.
*/
void
RelationMapFinishBootstrap(void)
{
Assert(IsBootstrapProcessingMode());
/* Shouldn't be anything "pending" ... */
Assert(active_shared_updates.num_mappings == 0);
Assert(active_local_updates.num_mappings == 0);
Assert(pending_shared_updates.num_mappings == 0);
Assert(pending_local_updates.num_mappings == 0);
/* Write the files; no WAL or sinval needed */
write_relmap_file(true, &shared_map, false, false, false,
InvalidOid, GLOBALTABLESPACE_OID, NULL);
write_relmap_file(false, &local_map, false, false, false,
MyDatabaseId, MyDatabaseTableSpace, DatabasePath);
}
/*
* RelationMapInitialize
*
* This initializes the mapper module at process startup. We can't access the
* database yet, so just make sure the maps are empty.
*/
void
RelationMapInitialize(void)
{
/* The static variables should initialize to zeroes, but let's be sure */
shared_map.magic = 0; /* mark it not loaded */
local_map.magic = 0;
shared_map.num_mappings = 0;
local_map.num_mappings = 0;
active_shared_updates.num_mappings = 0;
active_local_updates.num_mappings = 0;
pending_shared_updates.num_mappings = 0;
pending_local_updates.num_mappings = 0;
}
/*
* RelationMapInitializePhase2
*
* This is called to prepare for access to pg_database during startup.
* We should be able to read the shared map file now.
*/
void
RelationMapInitializePhase2(void)
{
/*
* In bootstrap mode, the map file isn't there yet, so do nothing.
*/
if (IsBootstrapProcessingMode())
return;
/*
* Load the shared map file, die on error.
*/
load_relmap_file(true);
}
/*
* RelationMapInitializePhase3
*
* This is called as soon as we have determined MyDatabaseId and set up
* DatabasePath. At this point we should be able to read the local map file.
*/
void
RelationMapInitializePhase3(void)
{
/*
* In bootstrap mode, the map file isn't there yet, so do nothing.
*/
if (IsBootstrapProcessingMode())
return;
/*
* Load the local map file, die on error.
*/
load_relmap_file(false);
}
/*
* load_relmap_file -- load data from the shared or local map file
*
* Because the map file is essential for access to core system catalogs,
* failure to read it is a fatal error.
*
* Note that the local case requires DatabasePath to be set up.
*/
static void
load_relmap_file(bool shared)
{
RelMapFile *map;
char mapfilename[MAXPGPATH];
pg_crc32c crc;
int fd;
if (shared)
{
snprintf(mapfilename, sizeof(mapfilename), "global/%s",
RELMAPPER_FILENAME);
map = &shared_map;
}
else
{
snprintf(mapfilename, sizeof(mapfilename), "%s/%s",
DatabasePath, RELMAPPER_FILENAME);
map = &local_map;
}
/* Read data ... */
fd = OpenTransientFile(mapfilename, O_RDONLY | PG_BINARY);
if (fd < 0)
ereport(FATAL,
(errcode_for_file_access(),
errmsg("could not open relation mapping file \"%s\": %m",
mapfilename)));
/*
* Note: we could take RelationMappingLock in shared mode here, but it
* seems unnecessary since our read() should be atomic against any
* concurrent updater's write(). If the file is updated shortly after we
* look, the sinval signaling mechanism will make us re-read it before we
* are able to access any relation that's affected by the change.
*/
pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_READ);
if (read(fd, map, sizeof(RelMapFile)) != sizeof(RelMapFile))
ereport(FATAL,
(errcode_for_file_access(),
errmsg("could not read relation mapping file \"%s\": %m",
mapfilename)));
pgstat_report_wait_end();
CloseTransientFile(fd);
/* check for correct magic number, etc */
if (map->magic != RELMAPPER_FILEMAGIC ||
map->num_mappings < 0 ||
map->num_mappings > MAX_MAPPINGS)
ereport(FATAL,
(errmsg("relation mapping file \"%s\" contains invalid data",
mapfilename)));
/* verify the CRC */
INIT_CRC32C(crc);
COMP_CRC32C(crc, (char *) map, offsetof(RelMapFile, crc));
FIN_CRC32C(crc);
if (!EQ_CRC32C(crc, map->crc))
ereport(FATAL,
(errmsg("relation mapping file \"%s\" contains incorrect checksum",
mapfilename)));
}
/*
* Write out a new shared or local map file with the given contents.
*
* The magic number and CRC are automatically updated in *newmap. On
* success, we copy the data to the appropriate permanent static variable.
*
* If write_wal is TRUE then an appropriate WAL message is emitted.
* (It will be false for bootstrap and WAL replay cases.)
*
* If send_sinval is TRUE then a SI invalidation message is sent.
* (This should be true except in bootstrap case.)
*
* If preserve_files is TRUE then the storage manager is warned not to
* delete the files listed in the map.
*
* Because this may be called during WAL replay when MyDatabaseId,
* DatabasePath, etc aren't valid, we require the caller to pass in suitable
* values. The caller is also responsible for being sure no concurrent
* map update could be happening.
*/
static void
write_relmap_file(bool shared, RelMapFile *newmap,
bool write_wal, bool send_sinval, bool preserve_files,
Oid dbid, Oid tsid, const char *dbpath)
{
int fd;
RelMapFile *realmap;
char mapfilename[MAXPGPATH];
/*
* Fill in the overhead fields and update CRC.
*/
newmap->magic = RELMAPPER_FILEMAGIC;
if (newmap->num_mappings < 0 || newmap->num_mappings > MAX_MAPPINGS)
elog(ERROR, "attempt to write bogus relation mapping");
INIT_CRC32C(newmap->crc);
COMP_CRC32C(newmap->crc, (char *) newmap, offsetof(RelMapFile, crc));
FIN_CRC32C(newmap->crc);
/*
* Open the target file. We prefer to do this before entering the
* critical section, so that an open() failure need not force PANIC.
*/
if (shared)
{
snprintf(mapfilename, sizeof(mapfilename), "global/%s",
RELMAPPER_FILENAME);
realmap = &shared_map;
}
else
{
snprintf(mapfilename, sizeof(mapfilename), "%s/%s",
dbpath, RELMAPPER_FILENAME);
realmap = &local_map;
}
fd = OpenTransientFile(mapfilename, O_WRONLY | O_CREAT | PG_BINARY);
if (fd < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open relation mapping file \"%s\": %m",
mapfilename)));
if (write_wal)
{
xl_relmap_update xlrec;
XLogRecPtr lsn;
/* now errors are fatal ... */
START_CRIT_SECTION();
xlrec.dbid = dbid;
xlrec.tsid = tsid;
xlrec.nbytes = sizeof(RelMapFile);
XLogBeginInsert();
XLogRegisterData((char *) (&xlrec), MinSizeOfRelmapUpdate);
XLogRegisterData((char *) newmap, sizeof(RelMapFile));
lsn = XLogInsert(RM_RELMAP_ID, XLOG_RELMAP_UPDATE);
/* As always, WAL must hit the disk before the data update does */
XLogFlush(lsn);
}
errno = 0;
pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_WRITE);
if (write(fd, newmap, sizeof(RelMapFile)) != sizeof(RelMapFile))
{
/* if write didn't set errno, assume problem is no disk space */
if (errno == 0)
errno = ENOSPC;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to relation mapping file \"%s\": %m",
mapfilename)));
}
pgstat_report_wait_end();
/*
* We choose to fsync the data to disk before considering the task done.
* It would be possible to relax this if it turns out to be a performance
* issue, but it would complicate checkpointing --- see notes for
* CheckPointRelationMap.
*/
pgstat_report_wait_start(WAIT_EVENT_RELATION_MAP_SYNC);
if (pg_fsync(fd) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not fsync relation mapping file \"%s\": %m",
mapfilename)));
pgstat_report_wait_end();
if (CloseTransientFile(fd))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not close relation mapping file \"%s\": %m",
mapfilename)));
/*
* Now that the file is safely on disk, send sinval message to let other
* backends know to re-read it. We must do this inside the critical
* section: if for some reason we fail to send the message, we have to
* force a database-wide PANIC. Otherwise other backends might continue
* execution with stale mapping information, which would be catastrophic
* as soon as others began to use the now-committed data.
*/
if (send_sinval)
CacheInvalidateRelmap(dbid);
/*
* Make sure that the files listed in the map are not deleted if the outer
* transaction aborts. This had better be within the critical section
* too: it's not likely to fail, but if it did, we'd arrive at transaction
* abort with the files still vulnerable. PANICing will leave things in a
* good state on-disk.
*
* Note: we're cheating a little bit here by assuming that mapped files
* are either in pg_global or the database's default tablespace.
*/
if (preserve_files)
{
int32 i;
for (i = 0; i < newmap->num_mappings; i++)
{
RelFileNode rnode;
rnode.spcNode = tsid;
rnode.dbNode = dbid;
rnode.relNode = newmap->mappings[i].mapfilenode;
RelationPreserveStorage(rnode, false);
}
}
/* Success, update permanent copy */
memcpy(realmap, newmap, sizeof(RelMapFile));
/* Critical section done */
if (write_wal)
END_CRIT_SECTION();
}
/*
* Merge the specified updates into the appropriate "real" map,
* and write out the changes. This function must be used for committing
* updates during normal multiuser operation.
*/
static void
perform_relmap_update(bool shared, const RelMapFile *updates)
{
RelMapFile newmap;
/*
* Anyone updating a relation's mapping info should take exclusive lock on
* that rel and hold it until commit. This ensures that there will not be
* concurrent updates on the same mapping value; but there could easily be
* concurrent updates on different values in the same file. We cover that
* by acquiring the RelationMappingLock, re-reading the target file to
* ensure it's up to date, applying the updates, and writing the data
* before releasing RelationMappingLock.
*
* There is only one RelationMappingLock. In principle we could try to
* have one per mapping file, but it seems unlikely to be worth the
* trouble.
*/
LWLockAcquire(RelationMappingLock, LW_EXCLUSIVE);
/* Be certain we see any other updates just made */
load_relmap_file(shared);
/* Prepare updated data in a local variable */
if (shared)
memcpy(&newmap, &shared_map, sizeof(RelMapFile));
else
memcpy(&newmap, &local_map, sizeof(RelMapFile));
/*
* Apply the updates to newmap. No new mappings should appear, unless
* somebody is adding indexes to system catalogs.
*/
merge_map_updates(&newmap, updates, allowSystemTableMods);
/* Write out the updated map and do other necessary tasks */
write_relmap_file(shared, &newmap, true, true, true,
(shared ? InvalidOid : MyDatabaseId),
(shared ? GLOBALTABLESPACE_OID : MyDatabaseTableSpace),
DatabasePath);
/* Now we can release the lock */
LWLockRelease(RelationMappingLock);
}
/*
* RELMAP resource manager's routines
*/
void
relmap_redo(XLogReaderState *record)
{
uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
/* Backup blocks are not used in relmap records */
Assert(!XLogRecHasAnyBlockRefs(record));
if (info == XLOG_RELMAP_UPDATE)
{
xl_relmap_update *xlrec = (xl_relmap_update *) XLogRecGetData(record);
RelMapFile newmap;
char *dbpath;
if (xlrec->nbytes != sizeof(RelMapFile))
elog(PANIC, "relmap_redo: wrong size %u in relmap update record",
xlrec->nbytes);
memcpy(&newmap, xlrec->data, sizeof(newmap));
/* We need to construct the pathname for this database */
dbpath = GetDatabasePath(xlrec->dbid, xlrec->tsid);
/*
* Write out the new map and send sinval, but of course don't write a
* new WAL entry. There's no surrounding transaction to tell to
* preserve files, either.
*
* There shouldn't be anyone else updating relmaps during WAL replay,
* so we don't bother to take the RelationMappingLock. We would need
* to do so if load_relmap_file needed to interlock against writers.
*/
write_relmap_file((xlrec->dbid == InvalidOid), &newmap,
false, true, false,
xlrec->dbid, xlrec->tsid, dbpath);
pfree(dbpath);
}
else
elog(PANIC, "relmap_redo: unknown op code %u", info);
}
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