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Commita904181

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committed
Another go-round on making GetRawDatabaseInfo behave as well as it can,
given the fundamental restriction of not looking at transaction commitdata in pg_log. Use code that is actually based on tqual.c rather thanad-hoc tests. Also write the tuple fetch loop using standard accessmacros rather than ad-hoc code.
1 parent8a0c9b1 commita904181

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1 file changed

+67
-34
lines changed

1 file changed

+67
-34
lines changed

‎src/backend/utils/misc/database.c

Lines changed: 67 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -8,13 +8,12 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/utils/misc/Attic/database.c,v 1.41 2000/11/1418:37:45 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/utils/misc/Attic/database.c,v 1.42 2001/01/1422:21:05 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
1515
#include"postgres.h"
1616

17-
#include<errno.h>
1817
#include<fcntl.h>
1918
#include<stdlib.h>
2019
#include<string.h>
@@ -28,6 +27,9 @@
2827
#include"utils/syscache.h"
2928

3029

30+
staticboolPhonyHeapTupleSatisfiesNow(HeapTupleHeadertuple);
31+
32+
3133
/*
3234
* ExpandDatabasePath resolves a proposed database path (obtained from
3335
* pg_database.datpath) to a full absolute path for further consumption.
@@ -136,11 +138,9 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
136138
{
137139
intdbfd;
138140
intnbytes;
139-
intmax,
140-
i;
141+
intpathlen;
141142
HeapTupleDatatup;
142143
Pagepg;
143-
PageHeaderph;
144144
char*dbfname;
145145
Form_pg_databasetup_db;
146146

@@ -157,7 +157,7 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
157157
#endif
158158

159159
if ((dbfd=open(dbfname,O_RDONLY |PG_BINARY,0))<0)
160-
elog(FATAL,"cannot open %s: %s",dbfname,strerror(errno));
160+
elog(FATAL,"cannot open %s: %m",dbfname);
161161

162162
pfree(dbfname);
163163

@@ -179,38 +179,38 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
179179
* ----------------
180180
*/
181181
pg= (Page)palloc(BLCKSZ);
182-
ph= (PageHeader)pg;
183182

184183
while ((nbytes=read(dbfd,pg,BLCKSZ))==BLCKSZ)
185184
{
186-
max=PageGetMaxOffsetNumber(pg);
185+
OffsetNumbermax=PageGetMaxOffsetNumber(pg);
186+
OffsetNumberlineoff;
187187

188188
/* look at each tuple on the page */
189-
for (i=0;i<max;i++)
189+
for (lineoff=FirstOffsetNumber;lineoff <=max;lineoff++)
190190
{
191-
intoffset;
191+
ItemIdlpp=PageGetItemId(pg,lineoff);
192192

193193
/* if it's a freed tuple, ignore it */
194-
if (!(ph->pd_linp[i].lp_flags&LP_USED))
194+
if (!ItemIdIsUsed(lpp))
195195
continue;
196196

197197
/* get a pointer to the tuple itself */
198-
offset= (int)ph->pd_linp[i].lp_off;
199198
tup.t_datamcxt=NULL;
200-
tup.t_data= (HeapTupleHeader)(((char*)pg)+offset);
199+
tup.t_data= (HeapTupleHeader)PageGetItem(pg,lpp);
201200

202-
/*
203-
* if the tuple has been deleted (the database was destroyed),
204-
* skip this tuple. XXX warning, will robinson: violation of
205-
* transaction semantics happens right here. we should check
206-
* to be sure that the xact that deleted this tuple actually
207-
* committed. Only way to do that at init time is to paw over
208-
* the log relation by hand, too. Instead we take the
209-
* conservative assumption that if someone tried to delete it,
210-
* it's gone. The other side of the coin is that we might
211-
* accept a tuple that was stored and never committed.All in
212-
* all, this code is pretty shaky.We will cross-check our
213-
* result in ReverifyMyDatabase() in postinit.c.
201+
/*--------------------
202+
* Check to see if tuple is valid (committed).
203+
*
204+
* XXX warning, will robinson: violation of transaction semantics
205+
* happens right here. We cannot really determine if the tuple
206+
* is valid without checking transaction commit status, and the
207+
* only way to do that at init time is to paw over pg_log by hand,
208+
* too. Instead of checking, we assume that the inserting
209+
* transaction committed, and that any deleting transaction did
210+
* also, unless shown otherwise by on-row commit status bits.
211+
*
212+
* All in all, this code is pretty shaky. We will cross-check
213+
* our result in ReverifyMyDatabase() in postinit.c.
214214
*
215215
* NOTE: if a bogus tuple in pg_database prevents connection to a
216216
* valid database, a fix is to connect to another database and
@@ -220,12 +220,10 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
220220
* XXX wouldn't it be better to let new backends read the
221221
* database OID from a flat file, handled the same way we
222222
* handle the password relation?
223+
*--------------------
223224
*/
224-
if (tup.t_data->t_infomask&HEAP_XMIN_INVALID)
225-
continue;/* inserting xact known aborted */
226-
if (TransactionIdIsValid((TransactionId)tup.t_data->t_xmax)&&
227-
!(tup.t_data->t_infomask&HEAP_XMAX_INVALID))
228-
continue;/* deleting xact happened, not known aborted */
225+
if (!PhonyHeapTupleSatisfiesNow(tup.t_data))
226+
continue;
229227

230228
/*
231229
* Okay, see if this is the one we want.
@@ -236,9 +234,11 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
236234
{
237235
/* Found it; extract the OID and the database path. */
238236
*db_id=tup.t_data->t_oid;
239-
strncpy(path,VARDATA(&(tup_db->datpath)),
240-
(VARSIZE(&(tup_db->datpath))-VARHDRSZ));
241-
*(path+VARSIZE(&(tup_db->datpath))-VARHDRSZ)='\0';
237+
pathlen=VARSIZE(&(tup_db->datpath))-VARHDRSZ;
238+
if (pathlen >=MAXPGPATH)
239+
pathlen=MAXPGPATH-1;/* pure paranoia */
240+
strncpy(path,VARDATA(&(tup_db->datpath)),pathlen);
241+
path[pathlen]='\0';
242242
gotodone;
243243
}
244244
}
@@ -251,4 +251,37 @@ GetRawDatabaseInfo(const char *name, Oid *db_id, char *path)
251251
done:
252252
close(dbfd);
253253
pfree(pg);
254-
}/* GetRawDatabaseInfo() */
254+
}
255+
256+
/*
257+
* PhonyHeapTupleSatisfiesNow --- cut-down tuple time qual test
258+
*
259+
* This is a simplified version of HeapTupleSatisfiesNow() that does not
260+
* depend on having transaction commit info available. Any transaction
261+
* that touched the tuple is assumed committed unless later marked invalid.
262+
* (While we could think about more complex rules, this seems appropriate
263+
* for examining pg_database, since both CREATE DATABASE and DROP DATABASE
264+
* are non-roll-back-able.)
265+
*/
266+
staticbool
267+
PhonyHeapTupleSatisfiesNow(HeapTupleHeadertuple)
268+
{
269+
if (!(tuple->t_infomask&HEAP_XMIN_COMMITTED))
270+
{
271+
if (tuple->t_infomask&HEAP_XMIN_INVALID)
272+
return false;
273+
274+
if (tuple->t_infomask&HEAP_MOVED_OFF)
275+
return false;
276+
/* else assume committed */
277+
}
278+
279+
if (tuple->t_infomask&HEAP_XMAX_INVALID)/* xid invalid or aborted */
280+
return true;
281+
282+
/* assume xmax transaction committed */
283+
if (tuple->t_infomask&HEAP_MARKED_FOR_UPDATE)
284+
return true;
285+
286+
return false;
287+
}

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