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Add pg_column_toast_chunk_id().

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This function returns the chunk_id of an on-disk TOASTed value.  If
the value is un-TOASTed or not on-disk, it returns NULL.  This is
useful for identifying which values are actually TOASTed and for
investigating "unexpected chunk number" errors.

Bumps catversion.

Author: Yugo Nagata
Reviewed-by: Jian He
Discussion: https://postgr.es/m/20230329105507.d764497456eeac1ca491b5bd%40sraoss.co.jp
This commit is contained in:
Nathan Bossart
2024-03-14 10:58:00 -05:00
parent 84c18acaf6
commit d1162cfda8
6 changed files with 90 additions and 1 deletions
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41
src/backend/utils/adt/varlena.c
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@@ -5105,6 +5105,47 @@ pg_column_compression(PG_FUNCTION_ARGS)
PG_RETURN_TEXT_P(cstring_to_text(result));
}
/*
* Return the chunk_id of the on-disk TOASTed value. Return NULL if the value
* is un-TOASTed or not on-disk.
*/
Datum
pg_column_toast_chunk_id(PG_FUNCTION_ARGS)
{
int typlen;
struct varlena *attr;
struct varatt_external toast_pointer;
/* On first call, get the input type's typlen, and save at *fn_extra */
if (fcinfo->flinfo->fn_extra == NULL)
{
/* Lookup the datatype of the supplied argument */
Oid argtypeid = get_fn_expr_argtype(fcinfo->flinfo, 0);
typlen = get_typlen(argtypeid);
if (typlen == 0) /* should not happen */
elog(ERROR, "cache lookup failed for type %u", argtypeid);
fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
sizeof(int));
*((int *) fcinfo->flinfo->fn_extra) = typlen;
}
else
typlen = *((int *) fcinfo->flinfo->fn_extra);
if (typlen != -1)
PG_RETURN_NULL();
attr = (struct varlena *) DatumGetPointer(PG_GETARG_DATUM(0));
if (!VARATT_IS_EXTERNAL_ONDISK(attr))
PG_RETURN_NULL();
VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
PG_RETURN_OID(toast_pointer.va_valueid);
}
/*
* string_agg - Concatenates values and returns string.
*