Hi,
I want to read an attribute value from a TupleTableSlot. When I try to
convert an attribute of SQL type varchar from Datum* to char* with the help
of the method TextDatumGetCString(...), sometimes there is a segmentation
fault. The segmentation fault comes from the method
TextDatumGetCString(...), which is defined in utils/builtins.h.
Unfortunately, the fault is not always reproducible. I debugged the code
and figured out that the value of result->tts_values[i] sometimes is
random. It may be uninitialized memory. In other cases, the variable value
is NULL. Then, I can just skip the conversion from Datum* to char*, so that
there is no segmentation fault. I attached a patch with the code. The
relevant line is:
char *value = TextDatumGetCString(result->tts_values[i]);
The SQL-Query is a simple "SELECT * from ..." on the TPC-H table customer.
About every third execution leads to a segmentation fault.
Why is the memory of the variable uninitialized?
I am not very familiar with Postgres. Is there another method to get a
varchar attribute out of a TupleTableSlot as string?
Best regards
Maria
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index 76dd62f..be05ad0 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -77,6 +77,7 @@
*/
#include "postgres.h"
+#include "catalog/pg_attribute.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "executor/nodeAppend.h"
@@ -112,6 +113,7 @@
#include "executor/nodeWindowAgg.h"
#include "executor/nodeWorktablescan.h"
#include "miscadmin.h"
+#include "utils/builtins.h"
/* ------------------------------------------------------------------------
@@ -509,6 +511,17 @@ ExecProcNode(PlanState *node)
if (node->instrument)
InstrStopNode(node->instrument, TupIsNull(result) ? 0.0 : 1.0);
+ int i;
+ for(i = 0; i < result->tts_tupleDescriptor->natts; i++) {
+ if (1042 == result->tts_tupleDescriptor->attrs[i]->atttypid) {
+ if (0 == result->tts_values[i]) {
+ printf("null found\n");
+ } else {
+ char *value = TextDatumGetCString(result->tts_values[i]);
+ }
+ }
+ }
+
return result;
}
--
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