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Introduce the 'force' option for the Drop Database command.

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This new option terminates the other sessions connected to the target
database and then drop it.  To terminate other sessions, the current user
must have desired permissions (same as pg_terminate_backend()).  We don't
allow to terminate the sessions if prepared transactions, active logical
replication slots or subscriptions are present in the target database.

Author: Pavel Stehule with changes by me
Reviewed-by: Dilip Kumar, Vignesh C, Ibrar Ahmed, Anthony Nowocien,
Ryan Lambert and Amit Kapila
Discussion: https://postgr.es/m/CAP_rwwmLJJbn70vLOZFpxGw3XD7nLB_7+NKz46H5EOO2k5H7OQ@mail.gmail.com
This commit is contained in:
Amit Kapila
2019-11-12 11:06:13 +05:30
parent 112caf9039
commit 1379fd537f
13 changed files with 248 additions and 14 deletions
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114
src/backend/storage/ipc/procarray.c
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@@ -52,6 +52,8 @@
#include "access/xact.h"
#include "access/xlog.h"
#include "catalog/catalog.h"
#include "catalog/pg_authid.h"
#include "commands/dbcommands.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/proc.h"
@@ -2970,6 +2972,118 @@ CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
return true; /* timed out, still conflicts */
}
/*
* Terminate existing connections to the specified database. This routine
* is used by the DROP DATABASE command when user has asked to forcefully
* drop the database.
*
* The current backend is always ignored; it is caller's responsibility to
* check whether the current backend uses the given DB, if it's important.
*
* It doesn't allow to terminate the connections even if there is a one
* backend with the prepared transaction in the target database.
*/
void
TerminateOtherDBBackends(Oid databaseId)
{
ProcArrayStruct *arrayP = procArray;
List *pids = NIL;
int nprepared = 0;
int i;
LWLockAcquire(ProcArrayLock, LW_SHARED);
for (i = 0; i < procArray->numProcs; i++)
{
int pgprocno = arrayP->pgprocnos[i];
PGPROC *proc = &allProcs[pgprocno];
if (proc->databaseId != databaseId)
continue;
if (proc == MyProc)
continue;
if (proc->pid != 0)
pids = lappend_int(pids, proc->pid);
else
nprepared++;
}
LWLockRelease(ProcArrayLock);
if (nprepared > 0)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_IN_USE),
errmsg("database \"%s\" is being used by prepared transaction",
get_database_name(databaseId)),
errdetail_plural("There is %d prepared transaction using the database.",
"There are %d prepared transactions using the database.",
nprepared,
nprepared)));
if (pids)
{
ListCell *lc;
/*
* Check whether we have the necessary rights to terminate other
* sessions. We don't terminate any session untill we ensure that we
* have rights on all the sessions to be terminated. These checks are
* the same as we do in pg_terminate_backend.
*
* In this case we don't raise some warnings - like "PID %d is not a
* PostgreSQL server process", because for us already finished session
* is not a problem.
*/
foreach(lc, pids)
{
int pid = lfirst_int(lc);
PGPROC *proc = BackendPidGetProc(pid);
if (proc != NULL)
{
/* Only allow superusers to signal superuser-owned backends. */
if (superuser_arg(proc->roleId) && !superuser())
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
(errmsg("must be a superuser to terminate superuser process"))));
/* Users can signal backends they have role membership in. */
if (!has_privs_of_role(GetUserId(), proc->roleId) &&
!has_privs_of_role(GetUserId(), DEFAULT_ROLE_SIGNAL_BACKENDID))
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
(errmsg("must be a member of the role whose process is being terminated or member of pg_signal_backend"))));
}
}
/*
* There's a race condition here: once we release the ProcArrayLock,
* it's possible for the session to exit before we issue kill. That
* race condition possibility seems too unlikely to worry about. See
* pg_signal_backend.
*/
foreach(lc, pids)
{
int pid = lfirst_int(lc);
PGPROC *proc = BackendPidGetProc(pid);
if (proc != NULL)
{
/*
* If we have setsid(), signal the backend's whole process
* group
*/
#ifdef HAVE_SETSID
(void) kill(-pid, SIGTERM);
#else
(void) kill(pid, SIGTERM);
#endif
}
}
}
}
/*
* ProcArraySetReplicationSlotXmin
*