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* [PATCH 1/5] bootstrap: convert Typ to a List*
@ 2020-11-20 02:48 Justin Pryzby <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Justin Pryzby @ 2020-11-20 02:48 UTC (permalink / raw)
---
src/backend/bootstrap/bootstrap.c | 69 ++++++++++++++-----------------
1 file changed, 31 insertions(+), 38 deletions(-)
diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index 6f615e6622..18eb62ca47 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -159,7 +159,7 @@ struct typmap
FormData_pg_type am_typ;
};
-static struct typmap **Typ = NULL;
+static List *Typ = NIL; /* List of struct typmap* */
static struct typmap *Ap = NULL;
static Datum values[MAXATTR]; /* current row's attribute values */
@@ -597,7 +597,7 @@ boot_openrel(char *relname)
* pg_type must be filled before any OPEN command is executed, hence we
* can now populate the Typ array if we haven't yet.
*/
- if (Typ == NULL)
+ if (Typ == NIL)
populate_typ_array();
if (boot_reldesc != NULL)
@@ -688,7 +688,7 @@ DefineAttr(char *name, char *type, int attnum, int nullness)
typeoid = gettype(type);
- if (Typ != NULL)
+ if (Typ != NIL)
{
attrtypes[attnum]->atttypid = Ap->am_oid;
attrtypes[attnum]->attlen = Ap->am_typ.typlen;
@@ -877,36 +877,25 @@ populate_typ_array(void)
Relation rel;
TableScanDesc scan;
HeapTuple tup;
- int nalloc;
- int i;
-
- Assert(Typ == NULL);
- nalloc = 512;
- Typ = (struct typmap **)
- MemoryContextAlloc(TopMemoryContext, nalloc * sizeof(struct typmap *));
+ Assert(Typ == NIL);
rel = table_open(TypeRelationId, NoLock);
scan = table_beginscan_catalog(rel, 0, NULL);
- i = 0;
while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
{
Form_pg_type typForm = (Form_pg_type) GETSTRUCT(tup);
+ struct typmap *newtyp;
+ MemoryContext old;
- /* make sure there will be room for a trailing NULL pointer */
- if (i >= nalloc - 1)
- {
- nalloc *= 2;
- Typ = (struct typmap **)
- repalloc(Typ, nalloc * sizeof(struct typmap *));
- }
- Typ[i] = (struct typmap *)
- MemoryContextAlloc(TopMemoryContext, sizeof(struct typmap));
- Typ[i]->am_oid = typForm->oid;
- memcpy(&(Typ[i]->am_typ), typForm, sizeof(Typ[i]->am_typ));
- i++;
+ old = MemoryContextSwitchTo(TopMemoryContext);
+ newtyp = (struct typmap *) palloc(sizeof(struct typmap));
+ Typ = lappend(Typ, newtyp);
+ MemoryContextSwitchTo(old);
+
+ newtyp->am_oid = typForm->oid;
+ memcpy(&newtyp->am_typ, typForm, sizeof(newtyp->am_typ));
}
- Typ[i] = NULL; /* Fill trailing NULL pointer */
table_endscan(scan);
table_close(rel, NoLock);
}
@@ -925,16 +914,17 @@ populate_typ_array(void)
static Oid
gettype(char *type)
{
- if (Typ != NULL)
+ if (Typ != NIL)
{
- struct typmap **app;
+ ListCell *lc;
- for (app = Typ; *app != NULL; app++)
+ foreach (lc, Typ)
{
- if (strncmp(NameStr((*app)->am_typ.typname), type, NAMEDATALEN) == 0)
+ struct typmap *app = lfirst(lc);
+ if (strncmp(NameStr(app->am_typ.typname), type, NAMEDATALEN) == 0)
{
- Ap = *app;
- return (*app)->am_oid;
+ Ap = app;
+ return app->am_oid;
}
}
}
@@ -980,14 +970,17 @@ boot_get_type_io_data(Oid typid,
if (Typ != NULL)
{
/* We have the boot-time contents of pg_type, so use it */
- struct typmap **app;
- struct typmap *ap;
-
- app = Typ;
- while (*app && (*app)->am_oid != typid)
- ++app;
- ap = *app;
- if (ap == NULL)
+ struct typmap *ap = NULL;
+ ListCell *lc;
+
+ foreach (lc, Typ)
+ {
+ ap = lfirst(lc);
+ if (ap->am_oid == typid)
+ break;
+ }
+
+ if (!ap || ap->am_oid != typid)
elog(ERROR, "type OID %u not found in Typ list", typid);
*typlen = ap->am_typ.typlen;
--
2.26.2
--------------614DDB87AFFED893713AC0E9
Content-Type: text/x-patch; charset=UTF-8;
name="0002-Allow-composite-types-in-bootstrap-20210304.patch"
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
filename="0002-Allow-composite-types-in-bootstrap-20210304.patch"
^ permalink raw reply [nested|flat] 2+ messages in thread
* "38.10.10. Shared Memory and LWLocks" may require a clarification
@ 2023-05-19 15:49 Aleksander Alekseev <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Aleksander Alekseev @ 2023-05-19 15:49 UTC (permalink / raw)
To: PostgreSQL Hackers <[email protected]>
Hi,
While re-reading 38.10.10. Shared Memory and LWLocks [1] and the
corresponding code in pg_stat_statements.c I noticed that there are
several things that can puzzle the reader.
The documentation and the example suggest that LWLock* should be
stored within a structure in shared memory:
```
typedef struct pgssSharedState
{
LWLock *lock;
/* ... etc ... */
} pgssSharedState;
```
... and initialized like this:
```
LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
pgss = ShmemInitStruct("pg_stat_statements",
sizeof(pgssSharedState),
&found);
if (!found)
{
pgss->lock = &(GetNamedLWLockTranche("pg_stat_statements"))->lock;
/* ... */
}
/* ... */
LWLockRelease(AddinShmemInitLock);
```
It is not clear why placing LWLock* in a local process memory would be a bug.
On top of that the documentation says:
"""
To avoid possible race-conditions, each backend should use the LWLock
AddinShmemInitLock when connecting to and initializing its allocation
of shared memory
"""
However it's not clear when a race-condition may happen. The rest of
the text gives an overall impression that the shmem_startup_hook will
be called by postmaster once (unless an extension places several hooks
in series). Thus there is no real need to ackquire AddinShmemInitLock
and it should be safe to store LWLock* in local process memory. This
memory will be inherited from postmaster by child processes and the
overall memory usage is going to be the same due to copy-on-write.
Perhaps we should clarify this.
Thoughts?
[1]: https://www.postgresql.org/docs/15/xfunc-c.html#XFUNC-SHARED-ADDIN
--
Best regards,
Aleksander Alekseev
^ permalink raw reply [nested|flat] 2+ messages in thread
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2020-11-20 02:48 [PATCH 1/5] bootstrap: convert Typ to a List* Justin Pryzby <[email protected]>
2023-05-19 15:49 "38.10.10. Shared Memory and LWLocks" may require a clarification Aleksander Alekseev <[email protected]>
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