add support for LTTB downsampling on timescale.

tango-timeseries-persistence/src/main/java/fr/soleil/tango/archiving/event/db/mysql/select/MySqArchivingAttributeFetcher.java

@@ -111,4 +111,9 @@ public class MySqArchivingAttributeFetcher implements IArchivingAttributeFetcher
         //TODO
         return null;
     }
+
+    @Override
+    public AttributeValueSeries getWithSamplingLttb(final String attributeName, final int nbPoints, final Timestamp startTime, final Timestamp endTime) {
+        throw new TangoTimeseriesException("LTTB sampling method not supported for MySQL");
+    }
 }

tango-timeseries-persistence/src/main/java/fr/soleil/tango/archiving/event/db/timescale/select/ArchivingAttributeFetcher.java

@@ -167,5 +167,20 @@ public class ArchivingAttributeFetcher implements IArchivingAttributeFetcher {
         );
     }
 
+    @Override
+    public AttributeValueSeries getWithSamplingLttb(String attributeName, int nbPoints, Timestamp startTime, Timestamp endTime) {
+        AttributeConfig attributeConfigDB = config.getAttribute(attributeName);
+        if (attributeConfigDB == null) {
+            throw new TangoTimeseriesException(attributeName + " has never been stored");
+        }
+        final AttributeValueSeries buckets = jdbi.withExtension(AttributeQueries.class, dao ->
+                AttributeValueSeriesMapper.getAttributeValueSeries(attributeConfigDB,
+                        dao.selectWithSamplingLttb(attributeConfigDB.getTableName(),
+                                attributeConfigDB.getId(), nbPoints, startTime, endTime))
+        );
+        logger.debug("got {} values", buckets.getAttributeValues().size());
+        return buckets;
+    }
+
 
 }

tango-timeseries-persistence/src/main/java/fr/soleil/tango/archiving/event/db/timescale/select/AttributeQueries.java

@@ -46,9 +46,6 @@ import java.util.List;
 
 public interface AttributeQueries {
 
-    @SqlQuery("select distinct(att_conf_id) from <tableName> order by att_conf_id")
-    List<Integer> listID(@Define("tableName") String tableName);
-
     // select data_time, value_r, value_w, details from att_scalar_devdouble where att_scalar_devdouble.att_conf_id = 1 and data_time >  '2021-01-09 12:01:12.188'
     @SqlQuery("select att_conf_id, data_time, value_r, value_w, quality, details from <tableName>" +
             " where att_conf_id = :attConfID and data_time > :dataTime order by data_time")
@@ -138,8 +135,17 @@ public interface AttributeQueries {
             @Define("tableName") String tableName, @Define("aggregateFunction") String aggregateFunction,
             @Bind("attConfID") int attributeID, @Bind("startTime") Timestamp startTime, @Bind("endTime") Timestamp endTime);
 
-    // TODO
 
+    @SqlQuery("SELECT time as data_time, value as value_r FROM unnest(" +
+            "(select lttb(data_time, value_r, :nbPoint)FROM <tableName> " +
+            "where data_time >:startTime and data_time < :endTime and att_conf_id = :attConfID)) ORDER BY 1")
+    @RegisterFieldMapper(AttributeEventScalarTable.class)
+    List<AttributeEventScalarTable> selectWithSamplingLttb(@Define("tableName") String tableName, @Bind("attConfID") int attConfID, @Bind("nbPoint") int nbPoint,
+                                                           @Bind("startTime") Timestamp startTime, @Bind("endTime") Timestamp endTime);
+
+    // TODO
     // select data_time,value_r[1:4] from att_array_devfloat  where data_time between '2022-12-05 08:03:14.646 +01002' and '2022-12-06 08:03:14.646 +01002';
     // selectSubArrayBetween
+
+
 }

tango-timeseries-persistence/src/main/java/fr/soleil/tango/archiving/event/select/IArchivingAttributeFetcher.java

@@ -48,4 +48,6 @@ public interface IArchivingAttributeFetcher {
     AttributeValue getClosestValue(String attributeName, Timestamp timestamp, boolean withError);
 
     AttributeValue getAggregateValue(String attributeName, String aggregateFunction, Timestamp from, Timestamp to);
+
+    AttributeValueSeries getWithSamplingLttb(String attributeName, int nbPoints, Timestamp startTime, Timestamp endTime);
 }

tango-timeseries-persistence/src/test/java/fr/soleil/tango/archiving/services/TangoArchivingFetcherServiceTest.java

@@ -135,6 +135,18 @@ public class TangoArchivingFetcherServiceTest {
 
     }
 
+    @Test
+    public void selectWithSamplingLttb() {
+        final AttributeValueSeries result = fetcherService.getWithSamplingLttb("a/b/c/sin",
+                17, Timestamp.valueOf("2020-01-10 01:00:00.000"), Timestamp.valueOf("2020-04-21 00:00:00"));
+        System.out.println(result);
+        assertEquals(17, result.getAttributeValues().size());
+        assertEquals(12.7015115293407, result.getAttributeValues().get(0).getValueR());
+        assertEquals(Timestamp.valueOf("2020-01-11 01:00:00.000"), result.getAttributeValues().get(0).getDataTime());
+        assertEquals(10.022128489940254, result.getAttributeValues().get(16).getValueR());
+        assertEquals(Timestamp.valueOf("2020-04-20 02:00:00.0"), result.getAttributeValues().get(16).getDataTime());
+    }
+
     @Test
     public void getAttributeParameters() {
         final Optional<AttributeParameters> params = fetcherService.getAttributeParameters("BOO-C02/RP/CIG.038/ushort");

tango-timeseries-persistence/src/test/resources/timescaledb/V2__init.sql

@@ -33,3 +33,14 @@ VALUES(2, 'archiving/tdbarchiver/038', '2011-02-10 08:05:41.000', NULL, true, 60
 
 INSERT INTO contexts (context_id, name, description, is_active)
 VALUES(nextval('contexts_context_id_seq'), 'Technical shutdown', 'attributes paused during shutdowns', false);
+
+
+insert into att_conf values (nextval('att_conf_att_conf_id_seq'), 'a/b/c/sin', 5, 1, 1, 'att_scalar_devdouble', 'cs_name', 'a', 'b', 'c', 'sin', 0,false);
+
+SET TIME ZONE 'UTC';
+INSERT INTO att_scalar_devdouble(att_conf_id,data_time, value_r)
+    SELECT
+        8,
+        '2020-01-01 UTC'::TIMESTAMPTZ + make_interval(days=>(foo*10)::int) as data_time,
+        10 + 5 * cos(foo) as value_r
+    FROM generate_series(1,11,0.1) foo