Repair dimension slice table on update

This is a backport of timescale#2558.

In timescale#2800 a a race condition between inserts and `drop_chunks` is fixed
and this commit will repair the dimension slices table by
re-constructing missing dimension slices from the corresponding
constraint expressions.

sql/updates/latest-dev.sql

@@ -0,0 +1,78 @@
+-- Recreate missing dimension slices that might be missing. If the
+-- dimension slice table is broken and there are dimension slices
+-- missing from the table, we will repair it by:
+--
+--    1. Finding all chunk constraints that have missing dimension
+--       slices and extract the constraint expression from the
+--       associated constraint.
+--
+--    2. Parse the constraint expression and extract the column name,
+--       and upper and lower range values as text or, if it is a
+--       partition constraint, pick the existing constraint (either
+--       uppper or lower end of range) and make the other end open.
+--
+--    3. Use the column type to construct the range values (UNIX
+--       microseconds) from these strings.
+INSERT INTO _timescaledb_catalog.dimension_slice
+WITH
+   -- All dimension slices that are mentioned in the chunk_constraint
+   -- table but are missing from the dimension_slice table.
+   missing_slices AS (
+      SELECT hypertable_id,
+             chunk_id,
+             dimension_slice_id,
+             constraint_name,
+             attname AS column_name,
+             pg_get_expr(conbin, conrelid) AS constraint_expr
+      FROM _timescaledb_catalog.chunk_constraint cc
+      JOIN _timescaledb_catalog.chunk ch ON cc.chunk_id = ch.id
+      JOIN pg_constraint ON conname = constraint_name
+      JOIN pg_namespace ns ON connamespace = ns.oid AND ns.nspname = ch.schema_name
+      JOIN pg_attribute ON attnum = conkey[1] AND attrelid = conrelid
+      WHERE
+         dimension_slice_id NOT IN (SELECT id FROM _timescaledb_catalog.dimension_slice)
+   ),
+
+  -- Unparsed range start and end for each dimension slice id that
+  -- is missing.
+   unparsed_missing_slices AS (
+      SELECT di.id AS dimension_id,
+             dimension_slice_id,
+             constraint_name,
+             column_type,
+             column_name,
+             (SELECT SUBSTRING(constraint_expr, $$>=\s*'?([\w\d\s:+-]+)'?$$)) AS range_start,
+             (SELECT SUBSTRING(constraint_expr, $$<\s*'?([\w\d\s:+-]+)'?$$)) AS range_end
+        FROM missing_slices JOIN _timescaledb_catalog.dimension di USING (hypertable_id, column_name)
+   )
+SELECT DISTINCT
+       dimension_slice_id,
+       dimension_id,
+       CASE
+       WHEN column_type = 'timestamptz'::regtype THEN
+            EXTRACT(EPOCH FROM range_start::timestamptz) * 1000000
+       WHEN column_type = 'timestamp'::regtype THEN
+            EXTRACT(EPOCH FROM range_start::timestamp) * 1000000
+       WHEN column_type = 'date'::regtype THEN
+            EXTRACT(EPOCH FROM range_start::date) * 1000000
+       ELSE
+            CASE
+            WHEN range_start IS NULL
+            THEN -9223372036854775808
+            ELSE range_start::bigint
+            END
+       END AS range_start,
+       CASE
+       WHEN column_type = 'timestamptz'::regtype THEN
+            EXTRACT(EPOCH FROM range_end::timestamptz) * 1000000
+       WHEN column_type = 'timestamp'::regtype THEN
+            EXTRACT(EPOCH FROM range_end::timestamp) * 1000000
+       WHEN column_type = 'date'::regtype THEN
+            EXTRACT(EPOCH FROM range_end::date) * 1000000
+       ELSE
+            CASE WHEN range_end IS NULL
+            THEN 9223372036854775807
+            ELSE range_end::bigint
+            END
+       END AS range_end
+  FROM unparsed_missing_slices;

test/sql/updates/post.post_insert.sql

@@ -10,6 +10,7 @@ CREATE OR REPLACE FUNCTION timescaledb_integrity_test()
     RETURNS VOID LANGUAGE PLPGSQL STABLE AS
 $BODY$
 DECLARE
+    dimension_slice RECORD;
     constraint_row RECORD;
     index_row      RECORD;
     chunk_count    INTEGER;
@@ -64,6 +65,13 @@ BEGIN
            RAISE EXCEPTION 'Missing chunk constraints for %. Expected %, but found %', constraint_row.conname, chunk_count, chunk_constraint_count;
         END IF;
     END LOOP;
+
+    FOR dimension_slice IN
+    SELECT chunk_id, dimension_slice_id FROM _timescaledb_catalog.chunk_constraint
+     WHERE dimension_slice_id NOT IN (SELECT id FROM _timescaledb_catalog.dimension_slice)
+    LOOP
+      RAISE EXCEPTION 'Missing dimension slice with id % for chunk %.', dimension_slice.dimension_slice_id, dimension_slice.chunk_id;
+    END LOOP;
 END;
 $BODY$;