Check overflow in delta calculation for delta compression.

Delta between two adjacent tuples has fixed size in CO blocks of 29 bits during
delta compression. So any value larger than it should be stored natively without
applying delta compression to it. In cases where adjacent values are two far
part delta calculation missed checking for overflows. Hence adding the check
that if its negative don't apply delta compression, as logic always subtracts
smaller number from larger number only for overflow case it will go
negative. Also, adding validation tests for the same.
Signed-off-by: NShreedhar Hardikar <shardikar@pivotal.io>

src/backend/utils/datumstream/datumstreamblock.c

@@ -3005,7 +3005,13 @@ DatumStreamBlockWrite_PerformDeltaCompression(
 			break;
 	}
 
-	if (delta > MAX_DELTA_SUPPORTED_DELTA_COMPRESSION)
+	/*
+	 * Check if delta value fits the storage reserved for it. Important is to
+	 * also check for overflow case, where delta goes negative. As logic above
+	 * always subtracts smaller number from larger, delta must be positive
+	 * except overflow case.
+	 */
+	if (delta < 0 || delta > MAX_DELTA_SUPPORTED_DELTA_COMPRESSION)
 	{
 		return DELTA_COMPRESSION_NOT_APPLIED;
 	}

src/test/regress/expected/rle.out

@@ -11039,6 +11039,29 @@ select * from rle_runtest;
 (10000 rows)
 
 drop table rle_runtest;
+-- This tests the delta compression's delta computation arithmetic. The bigint
+-- column is used for the same and values inserted are INT64_MIN to INT64_MAX
+-- to check extreme overflow case.
+CREATE TABLE rle_overflowtest (a INT, b BIGINT, c char) WITH (appendonly=true, compresstype=rle_type, orientation=column, compresslevel=1);
+NOTICE:  Table doesn't have 'DISTRIBUTED BY' clause -- Using column named 'a' as the Greenplum Database data distribution key for this table.
+HINT:  The 'DISTRIBUTED BY' clause determines the distribution of data. Make sure column(s) chosen are the optimal data distribution key to minimize skew.
+INSERT INTO rle_overflowtest VALUES (1,9223372036854775807,'a'), (1,-9,'b');
+INSERT INTO rle_overflowtest VALUES (1,-9,'c'), (1,9223372036854775807,'d');
+INSERT INTO rle_overflowtest VALUES (1,-9223372036854775808,'e'), (1,9223372036854775807,'f');
+INSERT INTO rle_overflowtest VALUES (1,9223372036854775807,'g'), (1,-9223372036854775808,'h');
+SELECT * FROM rle_overflowtest;
+ a |          b           | c 
+---+----------------------+---
+ 1 |  9223372036854775807 | a
+ 1 |                   -9 | b
+ 1 |                   -9 | c
+ 1 |  9223372036854775807 | d
+ 1 | -9223372036854775808 | e
+ 1 |  9223372036854775807 | f
+ 1 |  9223372036854775807 | g
+ 1 | -9223372036854775808 | h
+(8 rows)
+
 DROP TABLE if exists CO_1_create_table_storage_directive_RLE_TYPE_8192_1;
 NOTICE:  table "co_1_create_table_storage_directive_rle_type_8192_1" does not exist, skipping
 --

src/test/regress/sql/rle.sql

@@ -20,6 +20,16 @@ insert into rle_runtest select 1, 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' FROM generate
 select * from rle_runtest;
 drop table rle_runtest;
 
+-- This tests the delta compression's delta computation arithmetic. The bigint
+-- column is used for the same and values inserted are INT64_MIN to INT64_MAX
+-- to check extreme overflow case.
+CREATE TABLE rle_overflowtest (a INT, b BIGINT, c char) WITH (appendonly=true, compresstype=rle_type, orientation=column, compresslevel=1);
+INSERT INTO rle_overflowtest VALUES (1,9223372036854775807,'a'), (1,-9,'b');
+INSERT INTO rle_overflowtest VALUES (1,-9,'c'), (1,9223372036854775807,'d');
+INSERT INTO rle_overflowtest VALUES (1,-9223372036854775808,'e'), (1,9223372036854775807,'f');
+INSERT INTO rle_overflowtest VALUES (1,9223372036854775807,'g'), (1,-9223372036854775808,'h');
+SELECT * FROM rle_overflowtest;
+
 DROP TABLE if exists CO_1_create_table_storage_directive_RLE_TYPE_8192_1;
 
 --