Move ANALYZE after heap scan during compression

Depending on the statistics target, running ANALYZE on a chunk before
compression can cause a lot of random IO operations for chunks that
are bigger than the number of pages ANALYZE needs to read. By moving
that operation after the heap is loaded into memory for sorting,
we increase the chance of hitting cache and reducing disk operations
necessary to execute compression jobs.

tsl/src/compression/api.c

@@ -159,28 +159,14 @@ compresschunkcxt_init(CompressChunkCxt *cxt, Cache *hcache, Oid hypertable_relid
 }
 
 static void
-preserve_uncompressed_chunk_stats(Oid chunk_relid)
+disable_autovacuum_on_chunk(Oid chunk_relid)
 {
 	AlterTableCmd at_cmd = {
 		.type = T_AlterTableCmd,
 		.subtype = AT_SetRelOptions,
 		.def = (Node *) list_make1(
 			makeDefElem("autovacuum_enabled", (Node *) makeString("false"), -1)),
 	};
-	VacuumRelation vr = {
-		.type = T_VacuumRelation,
-		.relation = NULL,
-		.oid = chunk_relid,
-		.va_cols = NIL,
-	};
-	VacuumStmt vs = {
-		.type = T_VacuumStmt,
-		.rels = list_make1(&vr),
-		.is_vacuumcmd = false,
-		.options = NIL,
-	};
-
-	ExecVacuum(NULL, &vs, true);
 	ts_alter_table_with_event_trigger(chunk_relid, NULL, list_make1(&at_cmd), false);
 }
 
@@ -234,8 +220,8 @@ compress_chunk_impl(Oid hypertable_relid, Oid chunk_relid)
 	LockRelationOid(cxt.compress_ht->main_table_relid, AccessShareLock);
 	LockRelationOid(cxt.srcht_chunk->table_id, ShareLock);
 
-	/* Perform an analyze on the chunk to get up-to-date stats before compressing */
-	preserve_uncompressed_chunk_stats(chunk_relid);
+	/* Disabling autovacuum on chunk which should be empty while in compressed state */
+	disable_autovacuum_on_chunk(chunk_relid);
 
 	/* acquire locks on catalog tables to keep till end of txn */
 	LockRelationOid(catalog_get_table_id(ts_catalog_get(), HYPERTABLE_COMPRESSION),

tsl/src/compression/compression.c

@@ -20,6 +20,7 @@
 #include <funcapi.h>
 #include <libpq/pqformat.h>
 #include <miscadmin.h>
+#include <nodes/pg_list.h>
 #include <storage/lmgr.h>
 #include <storage/predicate.h>
 #include <utils/builtins.h>
@@ -390,6 +391,7 @@ static void compress_chunk_populate_sort_info_for_column(Oid table,
 														 const ColumnCompressionInfo *column,
 														 AttrNumber *att_nums, Oid *sort_operator,
 														 Oid *collation, bool *nulls_first);
+static void preserve_uncompressed_chunk_stats(Oid chunk_relid);
 
 static Tuplesortstate *
 compress_chunk_sort_relation(Relation in_rel, int n_keys, const ColumnCompressionInfo **keys)
@@ -441,6 +443,12 @@ compress_chunk_sort_relation(Relation in_rel, int n_keys, const ColumnCompressio
 
 	heap_endscan(heapScan);
 
+	/* Perform an analyze on the chunk to get up-to-date stats before compressing.
+	 * We do it at this point to reduce the amount of random IO operations
+	 * necessary in case the statistic target is larger than the chunk heap size.
+	 */
+	preserve_uncompressed_chunk_stats(in_rel->rd_id);
+
 	ExecDropSingleTupleTableSlot(heap_tuple_slot);
 
 	tuplesort_performsort(tuplesortstate);
@@ -488,6 +496,25 @@ compress_chunk_populate_sort_info_for_column(Oid table, const ColumnCompressionI
 	ReleaseSysCache(tp);
 }
 
+static void
+preserve_uncompressed_chunk_stats(Oid chunk_relid)
+{
+	VacuumRelation vr = {
+		.type = T_VacuumRelation,
+		.relation = NULL,
+		.oid = chunk_relid,
+		.va_cols = NIL,
+	};
+	VacuumStmt vs = {
+		.type = T_VacuumStmt,
+		.rels = list_make1(&vr),
+		.is_vacuumcmd = false,
+		.options = NIL,
+	};
+
+	ExecVacuum(NULL, &vs, true);
+}
+
 /********************
  ** row_compressor **
  ********************/