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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
304 lines
7.7 KiB
C
304 lines
7.7 KiB
C
/*-------------------------------------------------------------------------
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*
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* rawpage.c
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* Functions to extract a raw page as bytea and inspect it
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*
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* Access-method specific inspection functions are in separate files.
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*
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* Copyright (c) 2007-2020, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/pageinspect/rawpage.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/htup_details.h"
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#include "access/relation.h"
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#include "catalog/namespace.h"
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#include "catalog/pg_type.h"
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#include "funcapi.h"
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#include "miscadmin.h"
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#include "pageinspect.h"
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#include "storage/bufmgr.h"
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#include "storage/checksum.h"
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#include "utils/builtins.h"
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#include "utils/pg_lsn.h"
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#include "utils/rel.h"
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#include "utils/varlena.h"
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PG_MODULE_MAGIC;
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static bytea *get_raw_page_internal(text *relname, ForkNumber forknum,
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BlockNumber blkno);
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/*
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* get_raw_page
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*
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* Returns a copy of a page from shared buffers as a bytea
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*/
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PG_FUNCTION_INFO_V1(get_raw_page);
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Datum
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get_raw_page(PG_FUNCTION_ARGS)
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{
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text *relname = PG_GETARG_TEXT_PP(0);
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uint32 blkno = PG_GETARG_UINT32(1);
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bytea *raw_page;
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/*
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* We don't normally bother to check the number of arguments to a C
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* function, but here it's needed for safety because early 8.4 beta
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* releases mistakenly redefined get_raw_page() as taking three arguments.
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*/
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if (PG_NARGS() != 2)
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ereport(ERROR,
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(errmsg("wrong number of arguments to get_raw_page()"),
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errhint("Run the updated pageinspect.sql script.")));
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raw_page = get_raw_page_internal(relname, MAIN_FORKNUM, blkno);
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PG_RETURN_BYTEA_P(raw_page);
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}
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/*
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* get_raw_page_fork
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*
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* Same, for any fork
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*/
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PG_FUNCTION_INFO_V1(get_raw_page_fork);
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Datum
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get_raw_page_fork(PG_FUNCTION_ARGS)
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{
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text *relname = PG_GETARG_TEXT_PP(0);
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text *forkname = PG_GETARG_TEXT_PP(1);
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uint32 blkno = PG_GETARG_UINT32(2);
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bytea *raw_page;
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ForkNumber forknum;
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forknum = forkname_to_number(text_to_cstring(forkname));
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raw_page = get_raw_page_internal(relname, forknum, blkno);
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PG_RETURN_BYTEA_P(raw_page);
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}
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/*
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* workhorse
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*/
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static bytea *
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get_raw_page_internal(text *relname, ForkNumber forknum, BlockNumber blkno)
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{
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bytea *raw_page;
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RangeVar *relrv;
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Relation rel;
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char *raw_page_data;
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Buffer buf;
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if (!superuser())
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ereport(ERROR,
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(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
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errmsg("must be superuser to use raw page functions")));
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relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
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rel = relation_openrv(relrv, AccessShareLock);
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/* Check that this relation has storage */
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if (rel->rd_rel->relkind == RELKIND_VIEW)
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ereport(ERROR,
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(errcode(ERRCODE_WRONG_OBJECT_TYPE),
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errmsg("cannot get raw page from view \"%s\"",
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RelationGetRelationName(rel))));
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if (rel->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
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ereport(ERROR,
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(errcode(ERRCODE_WRONG_OBJECT_TYPE),
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errmsg("cannot get raw page from composite type \"%s\"",
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RelationGetRelationName(rel))));
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if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
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ereport(ERROR,
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(errcode(ERRCODE_WRONG_OBJECT_TYPE),
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errmsg("cannot get raw page from foreign table \"%s\"",
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RelationGetRelationName(rel))));
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if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
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ereport(ERROR,
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(errcode(ERRCODE_WRONG_OBJECT_TYPE),
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errmsg("cannot get raw page from partitioned table \"%s\"",
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RelationGetRelationName(rel))));
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if (rel->rd_rel->relkind == RELKIND_PARTITIONED_INDEX)
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ereport(ERROR,
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(errcode(ERRCODE_WRONG_OBJECT_TYPE),
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errmsg("cannot get raw page from partitioned index \"%s\"",
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RelationGetRelationName(rel))));
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/*
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* Reject attempts to read non-local temporary relations; we would be
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* likely to get wrong data since we have no visibility into the owning
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* session's local buffers.
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*/
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if (RELATION_IS_OTHER_TEMP(rel))
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ereport(ERROR,
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(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
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errmsg("cannot access temporary tables of other sessions")));
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if (blkno >= RelationGetNumberOfBlocksInFork(rel, forknum))
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("block number %u is out of range for relation \"%s\"",
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blkno, RelationGetRelationName(rel))));
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/* Initialize buffer to copy to */
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raw_page = (bytea *) palloc(BLCKSZ + VARHDRSZ);
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SET_VARSIZE(raw_page, BLCKSZ + VARHDRSZ);
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raw_page_data = VARDATA(raw_page);
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/* Take a verbatim copy of the page */
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buf = ReadBufferExtended(rel, forknum, blkno, RBM_NORMAL, NULL);
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LockBuffer(buf, BUFFER_LOCK_SHARE);
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memcpy(raw_page_data, BufferGetPage(buf), BLCKSZ);
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LockBuffer(buf, BUFFER_LOCK_UNLOCK);
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ReleaseBuffer(buf);
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relation_close(rel, AccessShareLock);
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return raw_page;
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}
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/*
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* get_page_from_raw
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*
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* Get a palloc'd, maxalign'ed page image from the result of get_raw_page()
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*
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* On machines with MAXALIGN = 8, the payload of a bytea is not maxaligned,
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* since it will start 4 bytes into a palloc'd value. On alignment-picky
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* machines, this will cause failures in accesses to 8-byte-wide values
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* within the page. We don't need to worry if accessing only 4-byte or
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* smaller fields, but when examining a struct that contains 8-byte fields,
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* use this function for safety.
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*/
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Page
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get_page_from_raw(bytea *raw_page)
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{
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Page page;
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int raw_page_size;
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raw_page_size = VARSIZE_ANY_EXHDR(raw_page);
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if (raw_page_size != BLCKSZ)
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ereport(ERROR,
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(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
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errmsg("invalid page size"),
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errdetail("Expected %d bytes, got %d.",
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BLCKSZ, raw_page_size)));
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page = palloc(raw_page_size);
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memcpy(page, VARDATA_ANY(raw_page), raw_page_size);
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return page;
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}
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/*
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* page_header
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*
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* Allows inspection of page header fields of a raw page
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*/
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PG_FUNCTION_INFO_V1(page_header);
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Datum
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page_header(PG_FUNCTION_ARGS)
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{
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bytea *raw_page = PG_GETARG_BYTEA_P(0);
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TupleDesc tupdesc;
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Datum result;
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HeapTuple tuple;
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Datum values[9];
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bool nulls[9];
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PageHeader page;
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XLogRecPtr lsn;
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if (!superuser())
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ereport(ERROR,
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(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
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errmsg("must be superuser to use raw page functions")));
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page = (PageHeader) get_page_from_raw(raw_page);
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/* Build a tuple descriptor for our result type */
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if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
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elog(ERROR, "return type must be a row type");
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/* Extract information from the page header */
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lsn = PageGetLSN(page);
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/* pageinspect >= 1.2 uses pg_lsn instead of text for the LSN field. */
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if (TupleDescAttr(tupdesc, 0)->atttypid == TEXTOID)
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{
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char lsnchar[64];
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snprintf(lsnchar, sizeof(lsnchar), "%X/%X",
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(uint32) (lsn >> 32), (uint32) lsn);
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values[0] = CStringGetTextDatum(lsnchar);
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}
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else
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values[0] = LSNGetDatum(lsn);
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values[1] = UInt16GetDatum(page->pd_checksum);
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values[2] = UInt16GetDatum(page->pd_flags);
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values[3] = UInt16GetDatum(page->pd_lower);
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values[4] = UInt16GetDatum(page->pd_upper);
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values[5] = UInt16GetDatum(page->pd_special);
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values[6] = UInt16GetDatum(PageGetPageSize(page));
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values[7] = UInt16GetDatum(PageGetPageLayoutVersion(page));
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values[8] = TransactionIdGetDatum(page->pd_prune_xid);
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/* Build and return the tuple. */
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memset(nulls, 0, sizeof(nulls));
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tuple = heap_form_tuple(tupdesc, values, nulls);
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result = HeapTupleGetDatum(tuple);
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PG_RETURN_DATUM(result);
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}
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/*
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* page_checksum
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*
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* Compute checksum of a raw page
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*/
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PG_FUNCTION_INFO_V1(page_checksum);
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Datum
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page_checksum(PG_FUNCTION_ARGS)
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{
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bytea *raw_page = PG_GETARG_BYTEA_P(0);
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uint32 blkno = PG_GETARG_INT32(1);
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Page page;
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if (!superuser())
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ereport(ERROR,
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(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
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errmsg("must be superuser to use raw page functions")));
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page = get_page_from_raw(raw_page);
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if (PageIsNew(page))
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PG_RETURN_NULL();
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PG_RETURN_INT16(pg_checksum_page((char *) page, blkno));
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}
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