postgresql/contrib/pg_visibility/pg_visibility.c
Andres Freund 578b229718 Remove WITH OIDS support, change oid catalog column visibility.
Previously tables declared WITH OIDS, including a significant fraction
of the catalog tables, stored the oid column not as a normal column,
but as part of the tuple header.

This special column was not shown by default, which was somewhat odd,
as it's often (consider e.g. pg_class.oid) one of the more important
parts of a row.  Neither pg_dump nor COPY included the contents of the
oid column by default.

The fact that the oid column was not an ordinary column necessitated a
significant amount of special case code to support oid columns. That
already was painful for the existing, but upcoming work aiming to make
table storage pluggable, would have required expanding and duplicating
that "specialness" significantly.

WITH OIDS has been deprecated since 2005 (commit ff02d0a05280e0).
Remove it.

Removing includes:
- CREATE TABLE and ALTER TABLE syntax for declaring the table to be
  WITH OIDS has been removed (WITH (oids[ = true]) will error out)
- pg_dump does not support dumping tables declared WITH OIDS and will
  issue a warning when dumping one (and ignore the oid column).
- restoring an pg_dump archive with pg_restore will warn when
  restoring a table with oid contents (and ignore the oid column)
- COPY will refuse to load binary dump that includes oids.
- pg_upgrade will error out when encountering tables declared WITH
  OIDS, they have to be altered to remove the oid column first.
- Functionality to access the oid of the last inserted row (like
  plpgsql's RESULT_OID, spi's SPI_lastoid, ...) has been removed.

The syntax for declaring a table WITHOUT OIDS (or WITH (oids = false)
for CREATE TABLE) is still supported. While that requires a bit of
support code, it seems unnecessary to break applications / dumps that
do not use oids, and are explicit about not using them.

The biggest user of WITH OID columns was postgres' catalog. This
commit changes all 'magic' oid columns to be columns that are normally
declared and stored. To reduce unnecessary query breakage all the
newly added columns are still named 'oid', even if a table's column
naming scheme would indicate 'reloid' or such.  This obviously
requires adapting a lot code, mostly replacing oid access via
HeapTupleGetOid() with access to the underlying Form_pg_*->oid column.

The bootstrap process now assigns oids for all oid columns in
genbki.pl that do not have an explicit value (starting at the largest
oid previously used), only oids assigned later by oids will be above
FirstBootstrapObjectId. As the oid column now is a normal column the
special bootstrap syntax for oids has been removed.

Oids are not automatically assigned during insertion anymore, all
backend code explicitly assigns oids with GetNewOidWithIndex(). For
the rare case that insertions into the catalog via SQL are called for
the new pg_nextoid() function can be used (which only works on catalog
tables).

The fact that oid columns on system tables are now normal columns
means that they will be included in the set of columns expanded
by * (i.e. SELECT * FROM pg_class will now include the table's oid,
previously it did not). It'd not technically be hard to hide oid
column by default, but that'd mean confusing behavior would either
have to be carried forward forever, or it'd cause breakage down the
line.

While it's not unlikely that further adjustments are needed, the
scope/invasiveness of the patch makes it worthwhile to get merge this
now. It's painful to maintain externally, too complicated to commit
after the code code freeze, and a dependency of a number of other
patches.

Catversion bump, for obvious reasons.

Author: Andres Freund, with contributions by John Naylor
Discussion: https://postgr.es/m/20180930034810.ywp2c7awz7opzcfr@alap3.anarazel.de
2018-11-20 16:00:17 -08:00

780 lines
22 KiB
C

/*-------------------------------------------------------------------------
*
* pg_visibility.c
* display visibility map information and page-level visibility bits
*
* Copyright (c) 2016-2018, PostgreSQL Global Development Group
*
* contrib/pg_visibility/pg_visibility.c
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup_details.h"
#include "access/visibilitymap.h"
#include "catalog/pg_type.h"
#include "catalog/storage_xlog.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/procarray.h"
#include "storage/smgr.h"
#include "utils/rel.h"
PG_MODULE_MAGIC;
typedef struct vbits
{
BlockNumber next;
BlockNumber count;
uint8 bits[FLEXIBLE_ARRAY_MEMBER];
} vbits;
typedef struct corrupt_items
{
BlockNumber next;
BlockNumber count;
ItemPointer tids;
} corrupt_items;
PG_FUNCTION_INFO_V1(pg_visibility_map);
PG_FUNCTION_INFO_V1(pg_visibility_map_rel);
PG_FUNCTION_INFO_V1(pg_visibility);
PG_FUNCTION_INFO_V1(pg_visibility_rel);
PG_FUNCTION_INFO_V1(pg_visibility_map_summary);
PG_FUNCTION_INFO_V1(pg_check_frozen);
PG_FUNCTION_INFO_V1(pg_check_visible);
PG_FUNCTION_INFO_V1(pg_truncate_visibility_map);
static TupleDesc pg_visibility_tupdesc(bool include_blkno, bool include_pd);
static vbits *collect_visibility_data(Oid relid, bool include_pd);
static corrupt_items *collect_corrupt_items(Oid relid, bool all_visible,
bool all_frozen);
static void record_corrupt_item(corrupt_items *items, ItemPointer tid);
static bool tuple_all_visible(HeapTuple tup, TransactionId OldestXmin,
Buffer buffer);
static void check_relation_relkind(Relation rel);
/*
* Visibility map information for a single block of a relation.
*
* Note: the VM code will silently return zeroes for pages past the end
* of the map, so we allow probes up to MaxBlockNumber regardless of the
* actual relation size.
*/
Datum
pg_visibility_map(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
int64 blkno = PG_GETARG_INT64(1);
int32 mapbits;
Relation rel;
Buffer vmbuffer = InvalidBuffer;
TupleDesc tupdesc;
Datum values[2];
bool nulls[2];
rel = relation_open(relid, AccessShareLock);
/* Only some relkinds have a visibility map */
check_relation_relkind(rel);
if (blkno < 0 || blkno > MaxBlockNumber)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid block number")));
tupdesc = pg_visibility_tupdesc(false, false);
MemSet(nulls, 0, sizeof(nulls));
mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
values[0] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0);
values[1] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0);
relation_close(rel, AccessShareLock);
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
/*
* Visibility map information for a single block of a relation, plus the
* page-level information for the same block.
*/
Datum
pg_visibility(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
int64 blkno = PG_GETARG_INT64(1);
int32 mapbits;
Relation rel;
Buffer vmbuffer = InvalidBuffer;
Buffer buffer;
Page page;
TupleDesc tupdesc;
Datum values[3];
bool nulls[3];
rel = relation_open(relid, AccessShareLock);
/* Only some relkinds have a visibility map */
check_relation_relkind(rel);
if (blkno < 0 || blkno > MaxBlockNumber)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid block number")));
tupdesc = pg_visibility_tupdesc(false, true);
MemSet(nulls, 0, sizeof(nulls));
mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
values[0] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0);
values[1] = BoolGetDatum((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0);
/* Here we have to explicitly check rel size ... */
if (blkno < RelationGetNumberOfBlocks(rel))
{
buffer = ReadBuffer(rel, blkno);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
values[2] = BoolGetDatum(PageIsAllVisible(page));
UnlockReleaseBuffer(buffer);
}
else
{
/* As with the vismap, silently return 0 for pages past EOF */
values[2] = BoolGetDatum(false);
}
relation_close(rel, AccessShareLock);
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
/*
* Visibility map information for every block in a relation.
*/
Datum
pg_visibility_map_rel(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
vbits *info;
if (SRF_IS_FIRSTCALL())
{
Oid relid = PG_GETARG_OID(0);
MemoryContext oldcontext;
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
funcctx->tuple_desc = pg_visibility_tupdesc(true, false);
/* collect_visibility_data will verify the relkind */
funcctx->user_fctx = collect_visibility_data(relid, false);
MemoryContextSwitchTo(oldcontext);
}
funcctx = SRF_PERCALL_SETUP();
info = (vbits *) funcctx->user_fctx;
if (info->next < info->count)
{
Datum values[3];
bool nulls[3];
HeapTuple tuple;
MemSet(nulls, 0, sizeof(nulls));
values[0] = Int64GetDatum(info->next);
values[1] = BoolGetDatum((info->bits[info->next] & (1 << 0)) != 0);
values[2] = BoolGetDatum((info->bits[info->next] & (1 << 1)) != 0);
info->next++;
tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
}
SRF_RETURN_DONE(funcctx);
}
/*
* Visibility map information for every block in a relation, plus the page
* level information for each block.
*/
Datum
pg_visibility_rel(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
vbits *info;
if (SRF_IS_FIRSTCALL())
{
Oid relid = PG_GETARG_OID(0);
MemoryContext oldcontext;
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
funcctx->tuple_desc = pg_visibility_tupdesc(true, true);
/* collect_visibility_data will verify the relkind */
funcctx->user_fctx = collect_visibility_data(relid, true);
MemoryContextSwitchTo(oldcontext);
}
funcctx = SRF_PERCALL_SETUP();
info = (vbits *) funcctx->user_fctx;
if (info->next < info->count)
{
Datum values[4];
bool nulls[4];
HeapTuple tuple;
MemSet(nulls, 0, sizeof(nulls));
values[0] = Int64GetDatum(info->next);
values[1] = BoolGetDatum((info->bits[info->next] & (1 << 0)) != 0);
values[2] = BoolGetDatum((info->bits[info->next] & (1 << 1)) != 0);
values[3] = BoolGetDatum((info->bits[info->next] & (1 << 2)) != 0);
info->next++;
tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
}
SRF_RETURN_DONE(funcctx);
}
/*
* Count the number of all-visible and all-frozen pages in the visibility
* map for a particular relation.
*/
Datum
pg_visibility_map_summary(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
Relation rel;
BlockNumber nblocks;
BlockNumber blkno;
Buffer vmbuffer = InvalidBuffer;
int64 all_visible = 0;
int64 all_frozen = 0;
TupleDesc tupdesc;
Datum values[2];
bool nulls[2];
rel = relation_open(relid, AccessShareLock);
/* Only some relkinds have a visibility map */
check_relation_relkind(rel);
nblocks = RelationGetNumberOfBlocks(rel);
for (blkno = 0; blkno < nblocks; ++blkno)
{
int32 mapbits;
/* Make sure we are interruptible. */
CHECK_FOR_INTERRUPTS();
/* Get map info. */
mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0)
++all_visible;
if ((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0)
++all_frozen;
}
/* Clean up. */
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
relation_close(rel, AccessShareLock);
tupdesc = CreateTemplateTupleDesc(2);
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "all_visible", INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "all_frozen", INT8OID, -1, 0);
tupdesc = BlessTupleDesc(tupdesc);
MemSet(nulls, 0, sizeof(nulls));
values[0] = Int64GetDatum(all_visible);
values[1] = Int64GetDatum(all_frozen);
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
/*
* Return the TIDs of non-frozen tuples present in pages marked all-frozen
* in the visibility map. We hope no one will ever find any, but there could
* be bugs, database corruption, etc.
*/
Datum
pg_check_frozen(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
corrupt_items *items;
if (SRF_IS_FIRSTCALL())
{
Oid relid = PG_GETARG_OID(0);
MemoryContext oldcontext;
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
/* collect_corrupt_items will verify the relkind */
funcctx->user_fctx = collect_corrupt_items(relid, false, true);
MemoryContextSwitchTo(oldcontext);
}
funcctx = SRF_PERCALL_SETUP();
items = (corrupt_items *) funcctx->user_fctx;
if (items->next < items->count)
SRF_RETURN_NEXT(funcctx, PointerGetDatum(&items->tids[items->next++]));
SRF_RETURN_DONE(funcctx);
}
/*
* Return the TIDs of not-all-visible tuples in pages marked all-visible
* in the visibility map. We hope no one will ever find any, but there could
* be bugs, database corruption, etc.
*/
Datum
pg_check_visible(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
corrupt_items *items;
if (SRF_IS_FIRSTCALL())
{
Oid relid = PG_GETARG_OID(0);
MemoryContext oldcontext;
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
/* collect_corrupt_items will verify the relkind */
funcctx->user_fctx = collect_corrupt_items(relid, true, false);
MemoryContextSwitchTo(oldcontext);
}
funcctx = SRF_PERCALL_SETUP();
items = (corrupt_items *) funcctx->user_fctx;
if (items->next < items->count)
SRF_RETURN_NEXT(funcctx, PointerGetDatum(&items->tids[items->next++]));
SRF_RETURN_DONE(funcctx);
}
/*
* Remove the visibility map fork for a relation. If there turn out to be
* any bugs in the visibility map code that require rebuilding the VM, this
* provides users with a way to do it that is cleaner than shutting down the
* server and removing files by hand.
*
* This is a cut-down version of RelationTruncate.
*/
Datum
pg_truncate_visibility_map(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
Relation rel;
rel = relation_open(relid, AccessExclusiveLock);
/* Only some relkinds have a visibility map */
check_relation_relkind(rel);
RelationOpenSmgr(rel);
rel->rd_smgr->smgr_vm_nblocks = InvalidBlockNumber;
visibilitymap_truncate(rel, 0);
if (RelationNeedsWAL(rel))
{
xl_smgr_truncate xlrec;
xlrec.blkno = 0;
xlrec.rnode = rel->rd_node;
xlrec.flags = SMGR_TRUNCATE_VM;
XLogBeginInsert();
XLogRegisterData((char *) &xlrec, sizeof(xlrec));
XLogInsert(RM_SMGR_ID, XLOG_SMGR_TRUNCATE | XLR_SPECIAL_REL_UPDATE);
}
/*
* Release the lock right away, not at commit time.
*
* It would be a problem to release the lock prior to commit if this
* truncate operation sends any transactional invalidation messages. Other
* backends would potentially be able to lock the relation without
* processing them in the window of time between when we release the lock
* here and when we sent the messages at our eventual commit. However,
* we're currently only sending a non-transactional smgr invalidation,
* which will have been posted to shared memory immediately from within
* visibilitymap_truncate. Therefore, there should be no race here.
*
* The reason why it's desirable to release the lock early here is because
* of the possibility that someone will need to use this to blow away many
* visibility map forks at once. If we can't release the lock until
* commit time, the transaction doing this will accumulate
* AccessExclusiveLocks on all of those relations at the same time, which
* is undesirable. However, if this turns out to be unsafe we may have no
* choice...
*/
relation_close(rel, AccessExclusiveLock);
/* Nothing to return. */
PG_RETURN_VOID();
}
/*
* Helper function to construct whichever TupleDesc we need for a particular
* call.
*/
static TupleDesc
pg_visibility_tupdesc(bool include_blkno, bool include_pd)
{
TupleDesc tupdesc;
AttrNumber maxattr = 2;
AttrNumber a = 0;
if (include_blkno)
++maxattr;
if (include_pd)
++maxattr;
tupdesc = CreateTemplateTupleDesc(maxattr);
if (include_blkno)
TupleDescInitEntry(tupdesc, ++a, "blkno", INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, ++a, "all_visible", BOOLOID, -1, 0);
TupleDescInitEntry(tupdesc, ++a, "all_frozen", BOOLOID, -1, 0);
if (include_pd)
TupleDescInitEntry(tupdesc, ++a, "pd_all_visible", BOOLOID, -1, 0);
Assert(a == maxattr);
return BlessTupleDesc(tupdesc);
}
/*
* Collect visibility data about a relation.
*
* Checks relkind of relid and will throw an error if the relation does not
* have a VM.
*/
static vbits *
collect_visibility_data(Oid relid, bool include_pd)
{
Relation rel;
BlockNumber nblocks;
vbits *info;
BlockNumber blkno;
Buffer vmbuffer = InvalidBuffer;
BufferAccessStrategy bstrategy = GetAccessStrategy(BAS_BULKREAD);
rel = relation_open(relid, AccessShareLock);
/* Only some relkinds have a visibility map */
check_relation_relkind(rel);
nblocks = RelationGetNumberOfBlocks(rel);
info = palloc0(offsetof(vbits, bits) + nblocks);
info->next = 0;
info->count = nblocks;
for (blkno = 0; blkno < nblocks; ++blkno)
{
int32 mapbits;
/* Make sure we are interruptible. */
CHECK_FOR_INTERRUPTS();
/* Get map info. */
mapbits = (int32) visibilitymap_get_status(rel, blkno, &vmbuffer);
if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0)
info->bits[blkno] |= (1 << 0);
if ((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0)
info->bits[blkno] |= (1 << 1);
/*
* Page-level data requires reading every block, so only get it if the
* caller needs it. Use a buffer access strategy, too, to prevent
* cache-trashing.
*/
if (include_pd)
{
Buffer buffer;
Page page;
buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
bstrategy);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
if (PageIsAllVisible(page))
info->bits[blkno] |= (1 << 2);
UnlockReleaseBuffer(buffer);
}
}
/* Clean up. */
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
relation_close(rel, AccessShareLock);
return info;
}
/*
* Returns a list of items whose visibility map information does not match
* the status of the tuples on the page.
*
* If all_visible is passed as true, this will include all items which are
* on pages marked as all-visible in the visibility map but which do not
* seem to in fact be all-visible.
*
* If all_frozen is passed as true, this will include all items which are
* on pages marked as all-frozen but which do not seem to in fact be frozen.
*
* Checks relkind of relid and will throw an error if the relation does not
* have a VM.
*/
static corrupt_items *
collect_corrupt_items(Oid relid, bool all_visible, bool all_frozen)
{
Relation rel;
BlockNumber nblocks;
corrupt_items *items;
BlockNumber blkno;
Buffer vmbuffer = InvalidBuffer;
BufferAccessStrategy bstrategy = GetAccessStrategy(BAS_BULKREAD);
TransactionId OldestXmin = InvalidTransactionId;
if (all_visible)
{
/* Don't pass rel; that will fail in recovery. */
OldestXmin = GetOldestXmin(NULL, PROCARRAY_FLAGS_VACUUM);
}
rel = relation_open(relid, AccessShareLock);
/* Only some relkinds have a visibility map */
check_relation_relkind(rel);
nblocks = RelationGetNumberOfBlocks(rel);
/*
* Guess an initial array size. We don't expect many corrupted tuples, so
* start with a small array. This function uses the "next" field to track
* the next offset where we can store an item (which is the same thing as
* the number of items found so far) and the "count" field to track the
* number of entries allocated. We'll repurpose these fields before
* returning.
*/
items = palloc0(sizeof(corrupt_items));
items->next = 0;
items->count = 64;
items->tids = palloc(items->count * sizeof(ItemPointerData));
/* Loop over every block in the relation. */
for (blkno = 0; blkno < nblocks; ++blkno)
{
bool check_frozen = false;
bool check_visible = false;
Buffer buffer;
Page page;
OffsetNumber offnum,
maxoff;
/* Make sure we are interruptible. */
CHECK_FOR_INTERRUPTS();
/* Use the visibility map to decide whether to check this page. */
if (all_frozen && VM_ALL_FROZEN(rel, blkno, &vmbuffer))
check_frozen = true;
if (all_visible && VM_ALL_VISIBLE(rel, blkno, &vmbuffer))
check_visible = true;
if (!check_visible && !check_frozen)
continue;
/* Read and lock the page. */
buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
bstrategy);
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer);
maxoff = PageGetMaxOffsetNumber(page);
/*
* The visibility map bits might have changed while we were acquiring
* the page lock. Recheck to avoid returning spurious results.
*/
if (check_frozen && !VM_ALL_FROZEN(rel, blkno, &vmbuffer))
check_frozen = false;
if (check_visible && !VM_ALL_VISIBLE(rel, blkno, &vmbuffer))
check_visible = false;
if (!check_visible && !check_frozen)
{
UnlockReleaseBuffer(buffer);
continue;
}
/* Iterate over each tuple on the page. */
for (offnum = FirstOffsetNumber;
offnum <= maxoff;
offnum = OffsetNumberNext(offnum))
{
HeapTupleData tuple;
ItemId itemid;
itemid = PageGetItemId(page, offnum);
/* Unused or redirect line pointers are of no interest. */
if (!ItemIdIsUsed(itemid) || ItemIdIsRedirected(itemid))
continue;
/* Dead line pointers are neither all-visible nor frozen. */
if (ItemIdIsDead(itemid))
{
ItemPointerSet(&(tuple.t_self), blkno, offnum);
record_corrupt_item(items, &tuple.t_self);
continue;
}
/* Initialize a HeapTupleData structure for checks below. */
ItemPointerSet(&(tuple.t_self), blkno, offnum);
tuple.t_data = (HeapTupleHeader) PageGetItem(page, itemid);
tuple.t_len = ItemIdGetLength(itemid);
tuple.t_tableOid = relid;
/*
* If we're checking whether the page is all-visible, we expect
* the tuple to be all-visible.
*/
if (check_visible &&
!tuple_all_visible(&tuple, OldestXmin, buffer))
{
TransactionId RecomputedOldestXmin;
/*
* Time has passed since we computed OldestXmin, so it's
* possible that this tuple is all-visible in reality even
* though it doesn't appear so based on our
* previously-computed value. Let's compute a new value so we
* can be certain whether there is a problem.
*
* From a concurrency point of view, it sort of sucks to
* retake ProcArrayLock here while we're holding the buffer
* exclusively locked, but it should be safe against
* deadlocks, because surely GetOldestXmin() should never take
* a buffer lock. And this shouldn't happen often, so it's
* worth being careful so as to avoid false positives.
*/
RecomputedOldestXmin = GetOldestXmin(NULL, PROCARRAY_FLAGS_VACUUM);
if (!TransactionIdPrecedes(OldestXmin, RecomputedOldestXmin))
record_corrupt_item(items, &tuple.t_self);
else
{
OldestXmin = RecomputedOldestXmin;
if (!tuple_all_visible(&tuple, OldestXmin, buffer))
record_corrupt_item(items, &tuple.t_self);
}
}
/*
* If we're checking whether the page is all-frozen, we expect the
* tuple to be in a state where it will never need freezing.
*/
if (check_frozen)
{
if (heap_tuple_needs_eventual_freeze(tuple.t_data))
record_corrupt_item(items, &tuple.t_self);
}
}
UnlockReleaseBuffer(buffer);
}
/* Clean up. */
if (vmbuffer != InvalidBuffer)
ReleaseBuffer(vmbuffer);
relation_close(rel, AccessShareLock);
/*
* Before returning, repurpose the fields to match caller's expectations.
* next is now the next item that should be read (rather than written) and
* count is now the number of items we wrote (rather than the number we
* allocated).
*/
items->count = items->next;
items->next = 0;
return items;
}
/*
* Remember one corrupt item.
*/
static void
record_corrupt_item(corrupt_items *items, ItemPointer tid)
{
/* enlarge output array if needed. */
if (items->next >= items->count)
{
items->count *= 2;
items->tids = repalloc(items->tids,
items->count * sizeof(ItemPointerData));
}
/* and add the new item */
items->tids[items->next++] = *tid;
}
/*
* Check whether a tuple is all-visible relative to a given OldestXmin value.
* The buffer should contain the tuple and should be locked and pinned.
*/
static bool
tuple_all_visible(HeapTuple tup, TransactionId OldestXmin, Buffer buffer)
{
HTSV_Result state;
TransactionId xmin;
state = HeapTupleSatisfiesVacuum(tup, OldestXmin, buffer);
if (state != HEAPTUPLE_LIVE)
return false; /* all-visible implies live */
/*
* Neither lazy_scan_heap nor heap_page_is_all_visible will mark a page
* all-visible unless every tuple is hinted committed. However, those hint
* bits could be lost after a crash, so we can't be certain that they'll
* be set here. So just check the xmin.
*/
xmin = HeapTupleHeaderGetXmin(tup->t_data);
if (!TransactionIdPrecedes(xmin, OldestXmin))
return false; /* xmin not old enough for all to see */
return true;
}
/*
* check_relation_relkind - convenience routine to check that relation
* is of the relkind supported by the callers
*/
static void
check_relation_relkind(Relation rel)
{
if (rel->rd_rel->relkind != RELKIND_RELATION &&
rel->rd_rel->relkind != RELKIND_MATVIEW &&
rel->rd_rel->relkind != RELKIND_TOASTVALUE)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("\"%s\" is not a table, materialized view, or TOAST table",
RelationGetRelationName(rel))));
}