Report progress of CREATE INDEX operations

This uses the progress reporting infrastructure added by c16dc1aca5,
adding support for CREATE INDEX and CREATE INDEX CONCURRENTLY.

There are two pieces to this: one is index-AM-agnostic, and the other is
AM-specific.  The latter is fairly elaborate for btrees, including
reportage for parallel index builds and the separate phases that btree
index creation uses; other index AMs, which are much simpler in their
building procedures, have simplistic reporting only, but that seems
sufficient, at least for non-concurrent builds.

The index-AM-agnostic part is fairly complete, providing insight into
the CONCURRENTLY wait phases as well as block-based progress during the
index validation table scan.  (The index validation index scan requires
patching each AM, which has not been included here.)

Reviewers: Rahila Syed, Pavan Deolasee, Tatsuro Yamada
Discussion: https://postgr.es/m/20181220220022.mg63bhk26zdpvmcj@alvherre.pgsql

src/include/access/amapi.h

@@ -108,6 +108,9 @@ typedef bool (*amproperty_function) (Oid index_oid, int attno,
 									 IndexAMProperty prop, const char *propname,
 									 bool *res, bool *isnull);
 
+/* name of phase as used in progress reporting */
+typedef char *(*ambuildphasename_function) (int64 phasenum);
+
 /* validate definition of an opclass for this AM */
 typedef bool (*amvalidate_function) (Oid opclassoid);
 
@@ -213,6 +216,7 @@ typedef struct IndexAmRoutine
 	amcostestimate_function amcostestimate;
 	amoptions_function amoptions;
 	amproperty_function amproperty; /* can be NULL */
+	ambuildphasename_function ambuildphasename;	/* can be NULL */
 	amvalidate_function amvalidate;
 	ambeginscan_function ambeginscan;
 	amrescan_function amrescan;

src/include/access/genam.h

@@ -45,6 +45,7 @@ typedef struct IndexVacuumInfo
 {
 	Relation	index;			/* the index being vacuumed */
 	bool		analyze_only;	/* ANALYZE (without any actual vacuum) */
+	bool		report_progress;	/* emit progress.h status reports */
 	bool		estimated_count;	/* num_heap_tuples is an estimate */
 	int			message_level;	/* ereport level for progress messages */
 	double		num_heap_tuples;	/* tuples remaining in heap */

src/include/access/nbtree.h

@@ -671,6 +671,16 @@ typedef BTScanOpaqueData *BTScanOpaque;
 #define SK_BT_DESC			(INDOPTION_DESC << SK_BT_INDOPTION_SHIFT)
 #define SK_BT_NULLS_FIRST	(INDOPTION_NULLS_FIRST << SK_BT_INDOPTION_SHIFT)
 
+/*
+ * Constant definition for progress reporting.  Phase numbers must match
+ * btbuildphasename.
+ */
+/* PROGRESS_CREATEIDX_SUBPHASE_INITIALIZE is 1 (see progress.h) */
+#define PROGRESS_BTREE_PHASE_INDEXBUILD_TABLESCAN		2
+#define PROGRESS_BTREE_PHASE_PERFORMSORT_1				3
+#define PROGRESS_BTREE_PHASE_PERFORMSORT_2				4
+#define PROGRESS_BTREE_PHASE_LEAF_LOAD					5
+
 /*
  * external entry points for btree, in nbtree.c
  */
@@ -784,6 +794,7 @@ extern bytea *btoptions(Datum reloptions, bool validate);
 extern bool btproperty(Oid index_oid, int attno,
 		   IndexAMProperty prop, const char *propname,
 		   bool *res, bool *isnull);
+extern char *btbuildphasename(int64 phasenum);
 extern IndexTuple _bt_truncate(Relation rel, IndexTuple lastleft,
 			 IndexTuple firstright, BTScanInsert itup_key);
 extern int _bt_keep_natts_fast(Relation rel, IndexTuple lastleft,

src/include/access/tableam.h

@@ -507,6 +507,7 @@ typedef struct TableAmRoutine
 										   struct IndexInfo *index_nfo,
 										   bool allow_sync,
 										   bool anyvisible,
+										   bool progress,
 										   BlockNumber start_blockno,
 										   BlockNumber end_blockno,
 										   IndexBuildCallback callback,
@@ -1369,6 +1370,8 @@ table_scan_analyze_next_tuple(TableScanDesc scan, TransactionId OldestXmin,
  * so here because the AM might reject some of the tuples for its own reasons,
  * such as being unable to store NULLs.
  *
+ * If 'progress', the PROGRESS_SCAN_BLOCKS_TOTAL counter is updated when
+ * starting the scan, and PROGRESS_SCAN_BLOCKS_DONE is updated as we go along.
  *
  * A side effect is to set indexInfo->ii_BrokenHotChain to true if we detect
  * any potentially broken HOT chains.  Currently, we set this if there are any
@@ -1382,6 +1385,7 @@ table_index_build_scan(Relation heap_rel,
 					   Relation index_rel,
 					   struct IndexInfo *index_nfo,
 					   bool allow_sync,
+					   bool progress,
 					   IndexBuildCallback callback,
 					   void *callback_state,
 					   TableScanDesc scan)
@@ -1391,6 +1395,7 @@ table_index_build_scan(Relation heap_rel,
 														index_nfo,
 														allow_sync,
 														false,
+														progress,
 														0,
 														InvalidBlockNumber,
 														callback,
@@ -1414,6 +1419,7 @@ table_index_build_range_scan(Relation heap_rel,
 							 struct IndexInfo *index_nfo,
 							 bool allow_sync,
 							 bool anyvisible,
+							 bool progress,
 							 BlockNumber start_blockno,
 							 BlockNumber numblocks,
 							 IndexBuildCallback callback,
@@ -1425,6 +1431,7 @@ table_index_build_range_scan(Relation heap_rel,
 														index_nfo,
 														allow_sync,
 														anyvisible,
+														progress,
 														start_blockno,
 														numblocks,
 														callback,