Another go-round on making GetRawDatabaseInfo behave as well as it can,
given the fundamental restriction of not looking at transaction commit data in pg_log. Use code that is actually based on tqual.c rather than ad-hoc tests. Also write the tuple fetch loop using standard access macros rather than ad-hoc code.
This commit is contained in:
Tom Lane
parent
8a0c9b17a5
commit
a904181a46
@ -8,13 +8,12 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/utils/misc/Attic/database.c,v 1.41 2000/11/14 18:37:45 tgl Exp $
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* $Header: /cvsroot/pgsql/src/backend/utils/misc/Attic/database.c,v 1.42 2001/01/14 22:21:05 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <errno.h>
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#include <fcntl.h>
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#include <stdlib.h>
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#include <string.h>
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@ -28,6 +27,9 @@
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#include "utils/syscache.h"
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static bool PhonyHeapTupleSatisfiesNow(HeapTupleHeader tuple);
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/*
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* ExpandDatabasePath resolves a proposed database path (obtained from
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* pg_database.datpath) to a full absolute path for further consumption.
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@ -136,11 +138,9 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
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{
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int dbfd;
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int nbytes;
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int max,
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i;
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int pathlen;
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HeapTupleData tup;
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Page pg;
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PageHeader ph;
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char *dbfname;
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Form_pg_database tup_db;
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@ -157,7 +157,7 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
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#endif
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if ((dbfd = open(dbfname, O_RDONLY | PG_BINARY, 0)) < 0)
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elog(FATAL, "cannot open %s: %s", dbfname, strerror(errno));
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elog(FATAL, "cannot open %s: %m", dbfname);
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pfree(dbfname);
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@ -179,38 +179,38 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
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* ----------------
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*/
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pg = (Page) palloc(BLCKSZ);
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ph = (PageHeader) pg;
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while ((nbytes = read(dbfd, pg, BLCKSZ)) == BLCKSZ)
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{
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max = PageGetMaxOffsetNumber(pg);
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OffsetNumber max = PageGetMaxOffsetNumber(pg);
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OffsetNumber lineoff;
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/* look at each tuple on the page */
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for (i = 0; i < max; i++)
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for (lineoff = FirstOffsetNumber; lineoff <= max; lineoff++)
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{
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int offset;
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ItemId lpp = PageGetItemId(pg, lineoff);
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/* if it's a freed tuple, ignore it */
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if (!(ph->pd_linp[i].lp_flags & LP_USED))
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if (!ItemIdIsUsed(lpp))
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continue;
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/* get a pointer to the tuple itself */
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offset = (int) ph->pd_linp[i].lp_off;
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tup.t_datamcxt = NULL;
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tup.t_data = (HeapTupleHeader) (((char *) pg) + offset);
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tup.t_data = (HeapTupleHeader) PageGetItem(pg, lpp);
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/*
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* if the tuple has been deleted (the database was destroyed),
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* skip this tuple. XXX warning, will robinson: violation of
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* transaction semantics happens right here. we should check
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* to be sure that the xact that deleted this tuple actually
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* committed. Only way to do that at init time is to paw over
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* the log relation by hand, too. Instead we take the
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* conservative assumption that if someone tried to delete it,
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* it's gone. The other side of the coin is that we might
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* accept a tuple that was stored and never committed. All in
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* all, this code is pretty shaky. We will cross-check our
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* result in ReverifyMyDatabase() in postinit.c.
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/*--------------------
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* Check to see if tuple is valid (committed).
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*
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* XXX warning, will robinson: violation of transaction semantics
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* happens right here. We cannot really determine if the tuple
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* is valid without checking transaction commit status, and the
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* only way to do that at init time is to paw over pg_log by hand,
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* too. Instead of checking, we assume that the inserting
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* transaction committed, and that any deleting transaction did
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* also, unless shown otherwise by on-row commit status bits.
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*
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* All in all, this code is pretty shaky. We will cross-check
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* our result in ReverifyMyDatabase() in postinit.c.
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*
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* NOTE: if a bogus tuple in pg_database prevents connection to a
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* valid database, a fix is to connect to another database and
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@ -220,12 +220,10 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
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* XXX wouldn't it be better to let new backends read the
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* database OID from a flat file, handled the same way we
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* handle the password relation?
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*--------------------
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*/
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if (tup.t_data->t_infomask & HEAP_XMIN_INVALID)
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continue; /* inserting xact known aborted */
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if (TransactionIdIsValid((TransactionId) tup.t_data->t_xmax) &&
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!(tup.t_data->t_infomask & HEAP_XMAX_INVALID))
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continue; /* deleting xact happened, not known aborted */
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if (! PhonyHeapTupleSatisfiesNow(tup.t_data))
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continue;
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/*
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* Okay, see if this is the one we want.
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@ -236,9 +234,11 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
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{
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/* Found it; extract the OID and the database path. */
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*db_id = tup.t_data->t_oid;
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strncpy(path, VARDATA(&(tup_db->datpath)),
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(VARSIZE(&(tup_db->datpath)) - VARHDRSZ));
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*(path + VARSIZE(&(tup_db->datpath)) - VARHDRSZ) = '\0';
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pathlen = VARSIZE(&(tup_db->datpath)) - VARHDRSZ;
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if (pathlen >= MAXPGPATH)
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pathlen = MAXPGPATH-1; /* pure paranoia */
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strncpy(path, VARDATA(&(tup_db->datpath)), pathlen);
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path[pathlen] = '\0';
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goto done;
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}
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}
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@ -251,4 +251,37 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
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done:
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close(dbfd);
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pfree(pg);
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} /* GetRawDatabaseInfo() */
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}
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/*
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* PhonyHeapTupleSatisfiesNow --- cut-down tuple time qual test
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*
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* This is a simplified version of HeapTupleSatisfiesNow() that does not
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* depend on having transaction commit info available. Any transaction
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* that touched the tuple is assumed committed unless later marked invalid.
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* (While we could think about more complex rules, this seems appropriate
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* for examining pg_database, since both CREATE DATABASE and DROP DATABASE
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* are non-roll-back-able.)
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*/
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static bool
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PhonyHeapTupleSatisfiesNow(HeapTupleHeader tuple)
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{
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if (!(tuple->t_infomask & HEAP_XMIN_COMMITTED))
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{
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if (tuple->t_infomask & HEAP_XMIN_INVALID)
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return false;
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if (tuple->t_infomask & HEAP_MOVED_OFF)
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return false;
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/* else assume committed */
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}
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if (tuple->t_infomask & HEAP_XMAX_INVALID) /* xid invalid or aborted */
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return true;
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/* assume xmax transaction committed */
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if (tuple->t_infomask & HEAP_MARKED_FOR_UPDATE)
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return true;
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return false;
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}
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