Merge pull request duckdb#12753 from Mytherin/alprdskipping

ALP/ALPRD: correctly skip when we are skipping fewer values than in a vector

src/include/duckdb/storage/compression/alp/alp_scan.hpp

@@ -177,12 +177,11 @@ struct AlpScanState : public SegmentScanState {
 public:
 	//! Skip the next 'skip_count' values, we don't store the values
 	void Skip(ColumnSegment &col_segment, idx_t skip_count) {
-
 		if (total_value_count != 0 && !VectorFinished()) {
 			// Finish skipping the current vector
-			idx_t to_skip = LeftInVector();
-			skip_count -= to_skip;
+			idx_t to_skip = MinValue<idx_t>(skip_count, LeftInVector());
 			ScanVector<T, true>(nullptr, to_skip);
+			skip_count -= to_skip;
 		}
 		// Figure out how many entire vectors we can skip
 		// For these vectors, we don't even need to process the metadata or values

src/include/duckdb/storage/compression/alprd/alprd_scan.hpp

@@ -184,12 +184,11 @@ struct AlpRDScanState : public SegmentScanState {
 public:
 	//! Skip the next 'skip_count' values, we don't store the values
 	void Skip(ColumnSegment &col_segment, idx_t skip_count) {
-
 		if (total_value_count != 0 && !VectorFinished()) {
 			// Finish skipping the current vector
-			idx_t to_skip = LeftInVector();
-			skip_count -= to_skip;
+			idx_t to_skip = MinValue<idx_t>(skip_count, LeftInVector());
 			ScanVector<EXACT_TYPE, true>(nullptr, to_skip);
+			skip_count -= to_skip;
 		}
 		// Figure out how many entire vectors we can skip
 		// For these vectors, we don't even need to process the metadata or values

test/sql/storage/compression/alp/alp_list_skip.test

@@ -0,0 +1,127 @@
+# name: test/sql/storage/compression/alp/alp_list_skip.test
+# description: Test skipping of small lists in alp
+# group: [alp]
+
+# load the DB from disk
+load __TEST_DIR__/test_alp_list_skip.db
+
+foreach comp alp alprd
+
+statement ok
+SET force_compression='${comp}'
+
+# Create a table with random doubles of limited precision compressed as Uncompressed
+# This data should achieve x6 compression ratio
+statement ok
+create or replace table list_doubles as select 5700 i, [5700.0] l UNION ALL select i, CASE WHEN i%128=0 THEN [i::DOUBLE] ELSE []::DOUBLE[] END as data from range(10000) tbl(i) union all select 5700, [i] FROM range(100) tbl(i);
+
+statement ok
+checkpoint
+
+query II
+SELECT * FROM list_doubles WHERE i=5700
+----
+5700	[5700.0]
+5700	[]
+5700	[0.0]
+5700	[1.0]
+5700	[2.0]
+5700	[3.0]
+5700	[4.0]
+5700	[5.0]
+5700	[6.0]
+5700	[7.0]
+5700	[8.0]
+5700	[9.0]
+5700	[10.0]
+5700	[11.0]
+5700	[12.0]
+5700	[13.0]
+5700	[14.0]
+5700	[15.0]
+5700	[16.0]
+5700	[17.0]
+5700	[18.0]
+5700	[19.0]
+5700	[20.0]
+5700	[21.0]
+5700	[22.0]
+5700	[23.0]
+5700	[24.0]
+5700	[25.0]
+5700	[26.0]
+5700	[27.0]
+5700	[28.0]
+5700	[29.0]
+5700	[30.0]
+5700	[31.0]
+5700	[32.0]
+5700	[33.0]
+5700	[34.0]
+5700	[35.0]
+5700	[36.0]
+5700	[37.0]
+5700	[38.0]
+5700	[39.0]
+5700	[40.0]
+5700	[41.0]
+5700	[42.0]
+5700	[43.0]
+5700	[44.0]
+5700	[45.0]
+5700	[46.0]
+5700	[47.0]
+5700	[48.0]
+5700	[49.0]
+5700	[50.0]
+5700	[51.0]
+5700	[52.0]
+5700	[53.0]
+5700	[54.0]
+5700	[55.0]
+5700	[56.0]
+5700	[57.0]
+5700	[58.0]
+5700	[59.0]
+5700	[60.0]
+5700	[61.0]
+5700	[62.0]
+5700	[63.0]
+5700	[64.0]
+5700	[65.0]
+5700	[66.0]
+5700	[67.0]
+5700	[68.0]
+5700	[69.0]
+5700	[70.0]
+5700	[71.0]
+5700	[72.0]
+5700	[73.0]
+5700	[74.0]
+5700	[75.0]
+5700	[76.0]
+5700	[77.0]
+5700	[78.0]
+5700	[79.0]
+5700	[80.0]
+5700	[81.0]
+5700	[82.0]
+5700	[83.0]
+5700	[84.0]
+5700	[85.0]
+5700	[86.0]
+5700	[87.0]
+5700	[88.0]
+5700	[89.0]
+5700	[90.0]
+5700	[91.0]
+5700	[92.0]
+5700	[93.0]
+5700	[94.0]
+5700	[95.0]
+5700	[96.0]
+5700	[97.0]
+5700	[98.0]
+5700	[99.0]
+
+endloop