Обсуждение: Question about savepoint level?

Hi, hackers

The TransactionStateData has savepointLevel field, however, I do not understand
what is savepoint level, it seems all savepoints have the same savepointLevel,
I want to know how the savepoint level changes.

-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.

On Mon, 24 Oct 2022 at 12:19, Japin Li <japinli@hotmail.com> wrote:
> Hi, hackers
>
> The TransactionStateData has savepointLevel field, however, I do not understand
> what is savepoint level, it seems all savepoints have the same savepointLevel,
> I want to know how the savepoint level changes.

I try to remove the savepointLevel, and it seems harmless.  Any thoughts?

-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.

From 1e5c015efc44bcf2bc93365e99740deb618eebfe Mon Sep 17 00:00:00 2001
From: Japin Li <japinli@hotmail.com>
Date: Mon, 24 Oct 2022 14:54:03 +0800
Subject: [PATCH v1] Remove useless savepoint level

---
 src/backend/access/transam/xact.c | 18 ------------------
 1 file changed, 18 deletions(-)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index fd5103a78e..e8a90a3a30 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -190,7 +190,6 @@ typedef struct TransactionStateData
     FullTransactionId fullTransactionId;    /* my FullTransactionId */
     SubTransactionId subTransactionId;    /* my subxact ID */
     char       *name;            /* savepoint name, if any */
-    int            savepointLevel; /* savepoint level */
     TransState    state;            /* low-level state */
     TBlockState blockState;        /* high-level state */
     int            nestingLevel;    /* transaction nesting depth */
@@ -3234,12 +3233,10 @@ CommitTransactionCommand(void)
         case TBLOCK_SUBRESTART:
             {
                 char       *name;
-                int            savepointLevel;
 
                 /* save name and keep Cleanup from freeing it */
                 name = s->name;
                 s->name = NULL;
-                savepointLevel = s->savepointLevel;
 
                 AbortSubTransaction();
                 CleanupSubTransaction();
@@ -3247,7 +3244,6 @@ CommitTransactionCommand(void)
                 DefineSavepoint(NULL);
                 s = CurrentTransactionState;    /* changed by push */
                 s->name = name;
-                s->savepointLevel = savepointLevel;
 
                 /* This is the same as TBLOCK_SUBBEGIN case */
                 AssertState(s->blockState == TBLOCK_SUBBEGIN);
@@ -3263,19 +3259,16 @@ CommitTransactionCommand(void)
         case TBLOCK_SUBABORT_RESTART:
             {
                 char       *name;
-                int            savepointLevel;
 
                 /* save name and keep Cleanup from freeing it */
                 name = s->name;
                 s->name = NULL;
-                savepointLevel = s->savepointLevel;
 
                 CleanupSubTransaction();
 
                 DefineSavepoint(NULL);
                 s = CurrentTransactionState;    /* changed by push */
                 s->name = name;
-                s->savepointLevel = savepointLevel;
 
                 /* This is the same as TBLOCK_SUBBEGIN case */
                 AssertState(s->blockState == TBLOCK_SUBBEGIN);
@@ -4352,11 +4345,6 @@ ReleaseSavepoint(const char *name)
                 (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
                  errmsg("savepoint \"%s\" does not exist", name)));
 
-    /* disallow crossing savepoint level boundaries */
-    if (target->savepointLevel != s->savepointLevel)
-        ereport(ERROR,
-                (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
-                 errmsg("savepoint \"%s\" does not exist within current savepoint level", name)));
 
     /*
      * Mark "commit pending" all subtransactions up to the target
@@ -4461,11 +4449,6 @@ RollbackToSavepoint(const char *name)
                 (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
                  errmsg("savepoint \"%s\" does not exist", name)));
 
-    /* disallow crossing savepoint level boundaries */
-    if (target->savepointLevel != s->savepointLevel)
-        ereport(ERROR,
-                (errcode(ERRCODE_S_E_INVALID_SPECIFICATION),
-                 errmsg("savepoint \"%s\" does not exist within current savepoint level", name)));
 
     /*
      * Mark "abort pending" all subtransactions up to the target
@@ -5253,7 +5236,6 @@ PushTransaction(void)
     s->parent = p;
     s->nestingLevel = p->nestingLevel + 1;
     s->gucNestLevel = NewGUCNestLevel();
-    s->savepointLevel = p->savepointLevel;
     s->state = TRANS_DEFAULT;
     s->blockState = TBLOCK_SUBBEGIN;
     GetUserIdAndSecContext(&s->prevUser, &s->prevSecContext);
-- 
2.25.1

On 2022-Oct-24, Richard Guo wrote:

> On Mon, Oct 24, 2022 at 3:00 PM Japin Li <japinli@hotmail.com> wrote:
> 
> > I try to remove the savepointLevel, and it seems harmless.  Any thoughts?
> 
> ISTM the savepointLevel always remains the same as what is in
> TopTransactionStateData after looking at the codes. Now I also get
> confused. Maybe what we want is nestingLevel?

This has already been discussed:
https://postgr.es/m/1317297307-sup-7945@alvh.no-ip.org
Now that we have transaction-controlling procedures, I think the next
step is to add the SQL-standard feature that allows savepoint level
control for them, which would make the savepointLevel no longer dead
code.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"You're _really_ hosed if the person doing the hiring doesn't understand
relational systems: you end up with a whole raft of programmers, none of
whom has had a Date with the clue stick."              (Andrew Sullivan)

On Mon, 24 Oct 2022 at 17:56, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> This has already been discussed:
> https://postgr.es/m/1317297307-sup-7945@alvh.no-ip.org

Sorry for my lazy search.

> Now that we have transaction-controlling procedures, I think the next
> step is to add the SQL-standard feature that allows savepoint level
> control for them, which would make the savepointLevel no longer dead
> code.

So the savepoint level is used for CREATE PROCEDURE ... OLD/NEW SAVEPOINT LEVEL
syntax [1], right?

[1] https://www.ibm.com/docs/en/db2/10.1.0?topic=statements-create-procedure-sql

-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.

On 2022-Oct-24, Japin Li wrote:

> On Mon, 24 Oct 2022 at 17:56, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:

> > Now that we have transaction-controlling procedures, I think the next
> > step is to add the SQL-standard feature that allows savepoint level
> > control for them, which would make the savepointLevel no longer dead
> > code.
> 
> So the savepoint level is used for CREATE PROCEDURE ... OLD/NEW SAVEPOINT LEVEL
> syntax [1], right?
> 
> [1] https://www.ibm.com/docs/en/db2/10.1.0?topic=statements-create-procedure-sql

Yeah, that's what I understand.  The default behavior is the current
behavior (OLD SAVEPOINT LEVEL).  In a procedure that specifies NEW
SAVEPOINT LEVEL trying to rollback a savepoint that was defined before
the procedure was called is an error, which sounds a useful protection.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"El sentido de las cosas no viene de las cosas, sino de
las inteligencias que las aplican a sus problemas diarios
en busca del progreso." (Ernesto Hernández-Novich)