postgresql/contrib/pageinspect/rawpage.c
Michael Paquier 5378d55cb2 pageinspect: Fix handling of all-zero pages
Getting from get_raw_page() an all-zero page is considered as a valid
case by the buffer manager and it can happen for example when finding a
corrupted page with zero_damaged_pages enabled (using zero_damaged_pages
to look at corrupted pages happens), or after a crash when a relation
file is extended before any WAL for its new data is generated (before a
vacuum or autovacuum job comes in to do some cleanup).

However, all the functions of pageinspect, as of the index AMs (except
hash that has its own idea of new pages), heap, the FSM or the page
header have never worked with all-zero pages, causing various crashes
when going through the page internals.

This commit changes all the pageinspect functions to be compliant with
all-zero pages, where the choice is made to return NULL or no rows for
SRFs when finding a new page.  get_raw_page() still works the same way,
returning a batch of zeros in the bytea of the page retrieved.  A hard
error could be used but NULL, while more invasive, is useful when
scanning relation files in full to get a batch of results for a single
relation in one query.  Tests are added for all the code paths
impacted.

Reported-by: Daria Lepikhova
Author: Michael Paquier
Discussion: https://postgr.es/m/561e187b-3549-c8d5-03f5-525c14e65bd0@postgrespro.ru
Backpatch-through: 10
2022-04-14 15:09:39 +09:00

305 lines
7.7 KiB
C

/*-------------------------------------------------------------------------
*
* rawpage.c
* Functions to extract a raw page as bytea and inspect it
*
* Access-method specific inspection functions are in separate files.
*
* Copyright (c) 2007-2019, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/pageinspect/rawpage.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "pageinspect.h"
#include "access/htup_details.h"
#include "access/relation.h"
#include "catalog/namespace.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/checksum.h"
#include "utils/builtins.h"
#include "utils/pg_lsn.h"
#include "utils/rel.h"
#include "utils/varlena.h"
PG_MODULE_MAGIC;
static bytea *get_raw_page_internal(text *relname, ForkNumber forknum,
BlockNumber blkno);
/*
* get_raw_page
*
* Returns a copy of a page from shared buffers as a bytea
*/
PG_FUNCTION_INFO_V1(get_raw_page);
Datum
get_raw_page(PG_FUNCTION_ARGS)
{
text *relname = PG_GETARG_TEXT_PP(0);
uint32 blkno = PG_GETARG_UINT32(1);
bytea *raw_page;
/*
* We don't normally bother to check the number of arguments to a C
* function, but here it's needed for safety because early 8.4 beta
* releases mistakenly redefined get_raw_page() as taking three arguments.
*/
if (PG_NARGS() != 2)
ereport(ERROR,
(errmsg("wrong number of arguments to get_raw_page()"),
errhint("Run the updated pageinspect.sql script.")));
raw_page = get_raw_page_internal(relname, MAIN_FORKNUM, blkno);
PG_RETURN_BYTEA_P(raw_page);
}
/*
* get_raw_page_fork
*
* Same, for any fork
*/
PG_FUNCTION_INFO_V1(get_raw_page_fork);
Datum
get_raw_page_fork(PG_FUNCTION_ARGS)
{
text *relname = PG_GETARG_TEXT_PP(0);
text *forkname = PG_GETARG_TEXT_PP(1);
uint32 blkno = PG_GETARG_UINT32(2);
bytea *raw_page;
ForkNumber forknum;
forknum = forkname_to_number(text_to_cstring(forkname));
raw_page = get_raw_page_internal(relname, forknum, blkno);
PG_RETURN_BYTEA_P(raw_page);
}
/*
* workhorse
*/
static bytea *
get_raw_page_internal(text *relname, ForkNumber forknum, BlockNumber blkno)
{
bytea *raw_page;
RangeVar *relrv;
Relation rel;
char *raw_page_data;
Buffer buf;
if (!superuser())
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
(errmsg("must be superuser to use raw page functions"))));
relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
rel = relation_openrv(relrv, AccessShareLock);
/* Check that this relation has storage */
if (rel->rd_rel->relkind == RELKIND_VIEW)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("cannot get raw page from view \"%s\"",
RelationGetRelationName(rel))));
if (rel->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("cannot get raw page from composite type \"%s\"",
RelationGetRelationName(rel))));
if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("cannot get raw page from foreign table \"%s\"",
RelationGetRelationName(rel))));
if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("cannot get raw page from partitioned table \"%s\"",
RelationGetRelationName(rel))));
if (rel->rd_rel->relkind == RELKIND_PARTITIONED_INDEX)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("cannot get raw page from partitioned index \"%s\"",
RelationGetRelationName(rel))));
/*
* Reject attempts to read non-local temporary relations; we would be
* likely to get wrong data since we have no visibility into the owning
* session's local buffers.
*/
if (RELATION_IS_OTHER_TEMP(rel))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions")));
if (blkno >= RelationGetNumberOfBlocksInFork(rel, forknum))
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("block number %u is out of range for relation \"%s\"",
blkno, RelationGetRelationName(rel))));
/* Initialize buffer to copy to */
raw_page = (bytea *) palloc(BLCKSZ + VARHDRSZ);
SET_VARSIZE(raw_page, BLCKSZ + VARHDRSZ);
raw_page_data = VARDATA(raw_page);
/* Take a verbatim copy of the page */
buf = ReadBufferExtended(rel, forknum, blkno, RBM_NORMAL, NULL);
LockBuffer(buf, BUFFER_LOCK_SHARE);
memcpy(raw_page_data, BufferGetPage(buf), BLCKSZ);
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
ReleaseBuffer(buf);
relation_close(rel, AccessShareLock);
return raw_page;
}
/*
* get_page_from_raw
*
* Get a palloc'd, maxalign'ed page image from the result of get_raw_page()
*
* On machines with MAXALIGN = 8, the payload of a bytea is not maxaligned,
* since it will start 4 bytes into a palloc'd value. On alignment-picky
* machines, this will cause failures in accesses to 8-byte-wide values
* within the page. We don't need to worry if accessing only 4-byte or
* smaller fields, but when examining a struct that contains 8-byte fields,
* use this function for safety.
*/
Page
get_page_from_raw(bytea *raw_page)
{
Page page;
int raw_page_size;
raw_page_size = VARSIZE_ANY_EXHDR(raw_page);
if (raw_page_size != BLCKSZ)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid page size"),
errdetail("Expected %d bytes, got %d.",
BLCKSZ, raw_page_size)));
page = palloc(raw_page_size);
memcpy(page, VARDATA_ANY(raw_page), raw_page_size);
return page;
}
/*
* page_header
*
* Allows inspection of page header fields of a raw page
*/
PG_FUNCTION_INFO_V1(page_header);
Datum
page_header(PG_FUNCTION_ARGS)
{
bytea *raw_page = PG_GETARG_BYTEA_P(0);
TupleDesc tupdesc;
Datum result;
HeapTuple tuple;
Datum values[9];
bool nulls[9];
PageHeader page;
XLogRecPtr lsn;
if (!superuser())
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
(errmsg("must be superuser to use raw page functions"))));
page = (PageHeader) get_page_from_raw(raw_page);
/* Build a tuple descriptor for our result type */
if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
elog(ERROR, "return type must be a row type");
/* Extract information from the page header */
lsn = PageGetLSN(page);
/* pageinspect >= 1.2 uses pg_lsn instead of text for the LSN field. */
if (TupleDescAttr(tupdesc, 0)->atttypid == TEXTOID)
{
char lsnchar[64];
snprintf(lsnchar, sizeof(lsnchar), "%X/%X",
(uint32) (lsn >> 32), (uint32) lsn);
values[0] = CStringGetTextDatum(lsnchar);
}
else
values[0] = LSNGetDatum(lsn);
values[1] = UInt16GetDatum(page->pd_checksum);
values[2] = UInt16GetDatum(page->pd_flags);
values[3] = UInt16GetDatum(page->pd_lower);
values[4] = UInt16GetDatum(page->pd_upper);
values[5] = UInt16GetDatum(page->pd_special);
values[6] = UInt16GetDatum(PageGetPageSize(page));
values[7] = UInt16GetDatum(PageGetPageLayoutVersion(page));
values[8] = TransactionIdGetDatum(page->pd_prune_xid);
/* Build and return the tuple. */
memset(nulls, 0, sizeof(nulls));
tuple = heap_form_tuple(tupdesc, values, nulls);
result = HeapTupleGetDatum(tuple);
PG_RETURN_DATUM(result);
}
/*
* page_checksum
*
* Compute checksum of a raw page
*/
PG_FUNCTION_INFO_V1(page_checksum);
Datum
page_checksum(PG_FUNCTION_ARGS)
{
bytea *raw_page = PG_GETARG_BYTEA_P(0);
uint32 blkno = PG_GETARG_INT32(1);
Page page;
if (!superuser())
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
(errmsg("must be superuser to use raw page functions"))));
page = get_page_from_raw(raw_page);
if (PageIsNew(page))
PG_RETURN_NULL();
PG_RETURN_INT16(pg_checksum_page((char *) page, blkno));
}