Use 2^32 modulo computation to convert signed integer to unsigned value since

abs() may give a different result.

This makes the redistribution code in sync with the way hash modulo is computed
elsewhere in the code

diff --git a/src/backend/pgxc/locator/redistrib.c b/src/backend/pgxc/locator/redistrib.c
index 3fc36af8d0f9e745107a47bff94c4d504c9dafb2..e57cf2e7d9895bc77852289c336e31509b9d0fad 100644 (file)
--- a/src/backend/pgxc/locator/redistrib.c
+++ b/src/backend/pgxc/locator/redistrib.c
@@ -752,8 +752,14 @@ distrib_delete_hash(RedistribState *distribState, ExecNodes *exec_nodes)
                /*
                 * Then build the WHERE clause for deletion.
                 * The condition that allows to keep the tuples on remote nodes
-                * is of the type "RemoteNodeNumber != abs(hash_func(dis_col)) % NumDatanodes".
-                * the remote Datanode has no knowledge of its position in cluster so this
+                * is of the type "RemoteNodeNumber != (hash_func(dis_col)) %
+                * NumDatanodes".
+                *
+                * (Earlier we were using abs(hashvalue), but that does not render the
+                * same result as (unsigned int) (signed value). So we must do a modulo
+                * 2^32 computation.
+                *
+                * The remote Datanode has no knowledge of its position in cluster so this
                 * number needs to be compiled locally on Coordinator.
                 * Taking the absolute value is necessary as hash may return a negative value.
                 * For hash distributions a condition with correct hash function is used.
@@ -762,11 +768,11 @@ distrib_delete_hash(RedistribState *distribState, ExecNodes *exec_nodes)
                 */
                buf2 = makeStringInfo();
                if (hashfuncname)
-                       appendStringInfo(buf2, "%s WHERE abs(%s(%s)) %% %d != %d",
+                       appendStringInfo(buf2, "%s WHERE ((2^32 + %s(%s))::bigint %% (2^32)::bigint) %% %d != %d",
                                                         buf->data, hashfuncname, colname,
                                                         list_length(locinfo->rl_nodeList), nodepos);
                else
-                       appendStringInfo(buf2, "%s WHERE abs(%s) %% %d != %d", buf->data, colname,
+                       appendStringInfo(buf2, "%s WHERE ((2^32 + %s)::bigint %% (2^32)::bigint) %% %d != %d", buf->data, colname,
                                                         list_length(locinfo->rl_nodeList), nodepos);
 
                /* Then launch this single query */