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Commit4eb2176

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Fix DROP {DATABASE,TABLESPACE} on Windows.
Previously, it was possible for DROP DATABASE, DROP TABLESPACE and ALTERDATABASE SET TABLESPACE to fail because other backends still had filehandles open for dropped tables. Windows won't allow a directorycontaining unlinked-but-still-open files to be unlinked. Tackle thisproblem by forcing all backends to close all smgr fds. No change forUnix systems, which don't suffer from the problem, but the new code pathcan be tested by Unix-based developers by definingUSE_BARRIER_SMGRRELEASE explicitly.It's possible that PROCSIGNAL_BARRIER_SMGRRELEASE will have morebug-fixing applications soon (under discussion). Note that this is thefirst user of the ProcSignalBarrier mechanism from commit16a4e4a. Itcould in principle be back-patched as far as 14, but since fieldcomplaints are rare and ProcSignalBarrier hasn't been battle-tested,that seems like a bad idea. Fix in master only, where these failureshave started to show up in automated testing due to new tests.Suggested-by: Andres Freund <andres@anarazel.de>Reviewed-by: Andres Freund <andres@anarazel.de>Reviewed-by: Daniel Gustafsson <daniel@yesql.se>Reviewed-by: Robert Haas <robertmhaas@gmail.com>Discussion:https://postgr.es/m/CA+hUKGLdemy2gBm80kz20GTe6hNVwoErE8KwcJk6-U56oStjtg@mail.gmail.com
1 parente5691cc commit4eb2176

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9 files changed

+77
-36
lines changed

9 files changed

+77
-36
lines changed

‎src/backend/commands/dbcommands.c

Lines changed: 16 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -997,12 +997,15 @@ dropdb(const char *dbname, bool missing_ok, bool force)
997997

998998
/*
999999
* Force a checkpoint to make sure the checkpointer has received the
1000-
* message sent by ForgetDatabaseSyncRequests. On Windows, this also
1001-
* ensures that background procs don't hold any open files, which would
1002-
* cause rmdir() to fail.
1000+
* message sent by ForgetDatabaseSyncRequests.
10031001
*/
10041002
RequestCheckpoint(CHECKPOINT_IMMEDIATE |CHECKPOINT_FORCE |CHECKPOINT_WAIT);
10051003

1004+
#if defined(USE_BARRIER_SMGRRELEASE)
1005+
/* Close all smgr fds in all backends. */
1006+
WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
1007+
#endif
1008+
10061009
/*
10071010
* Remove all tablespace subdirs belonging to the database.
10081011
*/
@@ -1251,6 +1254,11 @@ movedb(const char *dbname, const char *tblspcname)
12511254
RequestCheckpoint(CHECKPOINT_IMMEDIATE |CHECKPOINT_FORCE |CHECKPOINT_WAIT
12521255
|CHECKPOINT_FLUSH_ALL);
12531256

1257+
#if defined(USE_BARRIER_SMGRRELEASE)
1258+
/* Close all smgr fds in all backends. */
1259+
WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
1260+
#endif
1261+
12541262
/*
12551263
* Now drop all buffers holding data of the target database; they should
12561264
* no longer be dirty so DropDatabaseBuffers is safe.
@@ -2258,6 +2266,11 @@ dbase_redo(XLogReaderState *record)
22582266
/* Clean out the xlog relcache too */
22592267
XLogDropDatabase(xlrec->db_id);
22602268

2269+
#if defined(USE_BARRIER_SMGRRELEASE)
2270+
/* Close all sgmr fds in all backends. */
2271+
WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
2272+
#endif
2273+
22612274
for (i=0;i<xlrec->ntablespaces;i++)
22622275
{
22632276
dst_path=GetDatabasePath(xlrec->db_id,xlrec->tablespace_ids[i]);

‎src/backend/commands/tablespace.c

Lines changed: 20 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -536,15 +536,24 @@ DropTableSpace(DropTableSpaceStmt *stmt)
536536
* but we can't tell them apart from important data files that we
537537
* mustn't delete. So instead, we force a checkpoint which will clean
538538
* out any lingering files, and try again.
539-
*
540-
* XXX On Windows, an unlinked file persists in the directory listing
539+
*/
540+
RequestCheckpoint(CHECKPOINT_IMMEDIATE |CHECKPOINT_FORCE |CHECKPOINT_WAIT);
541+
542+
/*
543+
* On Windows, an unlinked file persists in the directory listing
541544
* until no process retains an open handle for the file. The DDL
542545
* commands that schedule files for unlink send invalidation messages
543-
* directing other PostgreSQL processes to close the files. DROP
544-
* TABLESPACE should not give up on the tablespace becoming empty
545-
* until all relevant invalidation processing is complete.
546+
* directing other PostgreSQL processes to close the files, but
547+
* nothing guarantees they'll be processed in time. So, we'll also
548+
* use a global barrier to ask all backends to close all files, and
549+
* wait until they're finished.
546550
*/
547-
RequestCheckpoint(CHECKPOINT_IMMEDIATE |CHECKPOINT_FORCE |CHECKPOINT_WAIT);
551+
#if defined(USE_BARRIER_SMGRRELEASE)
552+
LWLockRelease(TablespaceCreateLock);
553+
WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
554+
LWLockAcquire(TablespaceCreateLock,LW_EXCLUSIVE);
555+
#endif
556+
/* And now try again. */
548557
if (!destroy_tablespace_directories(tablespaceoid, false))
549558
{
550559
/* Still not empty, the files must be important then */
@@ -1582,6 +1591,11 @@ tblspc_redo(XLogReaderState *record)
15821591
*/
15831592
if (!destroy_tablespace_directories(xlrec->ts_id, true))
15841593
{
1594+
#if defined(USE_BARRIER_SMGRRELEASE)
1595+
/* Close all smgr fds in all backends. */
1596+
WaitForProcSignalBarrier(EmitProcSignalBarrier(PROCSIGNAL_BARRIER_SMGRRELEASE));
1597+
#endif
1598+
15851599
ResolveRecoveryConflictWithTablespace(xlrec->ts_id);
15861600

15871601
/*

‎src/backend/storage/ipc/procsignal.c

Lines changed: 3 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -28,6 +28,7 @@
2828
#include"storage/latch.h"
2929
#include"storage/proc.h"
3030
#include"storage/shmem.h"
31+
#include"storage/smgr.h"
3132
#include"storage/sinval.h"
3233
#include"tcop/tcopprot.h"
3334
#include"utils/memutils.h"
@@ -94,7 +95,6 @@ static ProcSignalSlot *MyProcSignalSlot = NULL;
9495
staticboolCheckProcSignal(ProcSignalReasonreason);
9596
staticvoidCleanupProcSignalState(intstatus,Datumarg);
9697
staticvoidResetProcSignalBarrierBits(uint32flags);
97-
staticboolProcessBarrierPlaceholder(void);
9898
staticinlineintGetNumProcSignalSlots(void);
9999

100100
/*
@@ -536,8 +536,8 @@ ProcessProcSignalBarrier(void)
536536
type= (ProcSignalBarrierType)pg_rightmost_one_pos32(flags);
537537
switch (type)
538538
{
539-
casePROCSIGNAL_BARRIER_PLACEHOLDER:
540-
processed=ProcessBarrierPlaceholder();
539+
casePROCSIGNAL_BARRIER_SMGRRELEASE:
540+
processed=ProcessBarrierSmgrRelease();
541541
break;
542542
}
543543

@@ -603,24 +603,6 @@ ResetProcSignalBarrierBits(uint32 flags)
603603
InterruptPending= true;
604604
}
605605

606-
staticbool
607-
ProcessBarrierPlaceholder(void)
608-
{
609-
/*
610-
* XXX. This is just a placeholder until the first real user of this
611-
* machinery gets committed. Rename PROCSIGNAL_BARRIER_PLACEHOLDER to
612-
* PROCSIGNAL_BARRIER_SOMETHING_ELSE where SOMETHING_ELSE is something
613-
* appropriately descriptive. Get rid of this function and instead have
614-
* ProcessBarrierSomethingElse. Most likely, that function should live in
615-
* the file pertaining to that subsystem, rather than here.
616-
*
617-
* The return value should be 'true' if the barrier was successfully
618-
* absorbed and 'false' if not. Note that returning 'false' can lead to
619-
* very frequent retries, so try hard to make that an uncommon case.
620-
*/
621-
return true;
622-
}
623-
624606
/*
625607
* CheckProcSignal - check to see if a particular reason has been
626608
* signaled, and clear the signal flag. Should be called after receiving

‎src/backend/storage/smgr/md.c

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -549,6 +549,12 @@ mdclose(SMgrRelation reln, ForkNumber forknum)
549549
}
550550
}
551551

552+
void
553+
mdrelease(void)
554+
{
555+
closeAllVfds();
556+
}
557+
552558
/*
553559
*mdprefetch() -- Initiate asynchronous read of the specified block of a relation
554560
*/

‎src/backend/storage/smgr/smgr.c

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -41,6 +41,7 @@ typedef struct f_smgr
4141
{
4242
void(*smgr_init) (void);/* may be NULL */
4343
void(*smgr_shutdown) (void);/* may be NULL */
44+
void(*smgr_release) (void);/* may be NULL */
4445
void(*smgr_open) (SMgrRelationreln);
4546
void(*smgr_close) (SMgrRelationreln,ForkNumberforknum);
4647
void(*smgr_create) (SMgrRelationreln,ForkNumberforknum,
@@ -69,6 +70,7 @@ static const f_smgr smgrsw[] = {
6970
{
7071
.smgr_init=mdinit,
7172
.smgr_shutdown=NULL,
73+
.smgr_release=mdrelease,
7274
.smgr_open=mdopen,
7375
.smgr_close=mdclose,
7476
.smgr_create=mdcreate,
@@ -693,3 +695,19 @@ AtEOXact_SMgr(void)
693695
smgrclose(rel);
694696
}
695697
}
698+
699+
/*
700+
* This routine is called when we are ordered to release all open files by a
701+
* ProcSignalBarrier.
702+
*/
703+
bool
704+
ProcessBarrierSmgrRelease(void)
705+
{
706+
for (inti=0;i<NSmgr;i++)
707+
{
708+
if (smgrsw[i].smgr_release)
709+
smgrsw[i].smgr_release();
710+
}
711+
712+
return true;
713+
}

‎src/include/pg_config_manual.h

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -152,6 +152,17 @@
152152
#defineEXEC_BACKEND
153153
#endif
154154

155+
/*
156+
* If USE_BARRIER_SMGRRELEASE is defined, certain code paths that unlink
157+
* directories will ask other backends to close all smgr file descriptors.
158+
* This is enabled on Windows, because otherwise unlinked but still open files
159+
* can prevent rmdir(containing_directory) from succeeding. On other
160+
* platforms, it can be defined to exercise those code paths.
161+
*/
162+
#if defined(WIN32)
163+
#defineUSE_BARRIER_SMGRRELEASE
164+
#endif
165+
155166
/*
156167
* Define this if your operating system supports link()
157168
*/

‎src/include/storage/md.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,7 @@
2323
externvoidmdinit(void);
2424
externvoidmdopen(SMgrRelationreln);
2525
externvoidmdclose(SMgrRelationreln,ForkNumberforknum);
26+
externvoidmdrelease(void);
2627
externvoidmdcreate(SMgrRelationreln,ForkNumberforknum,boolisRedo);
2728
externboolmdexists(SMgrRelationreln,ForkNumberforknum);
2829
externvoidmdunlink(RelFileNodeBackendrnode,ForkNumberforknum,boolisRedo);

‎src/include/storage/procsignal.h

Lines changed: 1 addition & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -49,12 +49,7 @@ typedef enum
4949

5050
typedefenum
5151
{
52-
/*
53-
* XXX. PROCSIGNAL_BARRIER_PLACEHOLDER should be replaced when the first
54-
* real user of the ProcSignalBarrier mechanism is added. It's just here
55-
* for now because we can't have an empty enum.
56-
*/
57-
PROCSIGNAL_BARRIER_PLACEHOLDER=0
52+
PROCSIGNAL_BARRIER_SMGRRELEASE/* ask smgr to close files */
5853
}ProcSignalBarrierType;
5954

6055
/*

‎src/include/storage/smgr.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -104,5 +104,6 @@ extern void smgrtruncate(SMgrRelation reln, ForkNumber *forknum,
104104
intnforks,BlockNumber*nblocks);
105105
externvoidsmgrimmedsync(SMgrRelationreln,ForkNumberforknum);
106106
externvoidAtEOXact_SMgr(void);
107+
externboolProcessBarrierSmgrRelease(void);
107108

108109
#endif/* SMGR_H */

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