slow sqlfunction (#42)

* rework array_dedup_append function

* array_dedup_append: implemented faster version

uses nested array remove for merge+deduplication

migration.sql

@@ -132,23 +132,21 @@ CREATE TABLE banking_stage_results_2.accounts_map_transaction_latest(
     tx_ids BIGINT[]
 );
 
-CREATE OR REPLACE FUNCTION __array_reverse(anyarray) RETURNS anyarray AS $$
-    SELECT ARRAY(
-        SELECT $1[i]
-        FROM generate_subscripts($1,1) AS s(i)
-        ORDER BY i DESC
-    );
-$$ LANGUAGE SQL STRICT IMMUTABLE;
-
-
 CREATE OR REPLACE FUNCTION array_dedup_append(base bigint[], append bigint[], n_limit int)
     RETURNS bigint[]
 AS $$
-    SELECT __array_reverse(array_agg(val)) FROM (
-        SELECT val FROM (
-            SELECT DISTINCT ON (val) pos, val FROM unnest(__array_reverse(array_cat(base, append))) WITH ORDINALITY as t(val, pos)
-        ) AS deduped
-        ORDER BY pos
-        LIMIT n_limit
-    ) AS result
-$$ LANGUAGE SQL STRICT IMMUTABLE;
+DECLARE
+	tmplist  bigint[];
+	el		bigint;
+	len int;
+BEGIN
+    tmplist := base;
+    FOREACH el IN ARRAY append LOOP
+            tmplist := array_remove(tmplist, el);
+            tmplist := tmplist || el;
+        END LOOP;
+
+    len := CARDINALITY(tmplist);
+    RETURN  tmplist[(len + 1 - n_limit):];
+END
+$$ LANGUAGE plpgsql IMMUTABLE CALLED ON NULL INPUT;

src/postgres.rs

@@ -454,7 +454,7 @@ impl PostgresSession {
             SELECT
                 acc_id,
                 array_dedup_append(
-                    COALESCE((SELECT tx_ids FROM banking_stage_results_2.accounts_map_transaction_latest WHERE acc_id=amt_new.acc_id ), array[]::bigint[]),
+                    (SELECT tx_ids FROM banking_stage_results_2.accounts_map_transaction_latest WHERE acc_id=amt_new.acc_id),
                     amt_new.tx_agged,
                     {limit}) AS tx_ids_agg
                 FROM amt_new