Fix duplicate words in comments

Remove accidentally duplicated words in code comments.

Author: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Discussion: https://postgr.es/m/87bl45t0co.fsf@wibble.ilmari.org

src/backend/access/transam/parallel.c

@@ -1534,7 +1534,7 @@ ParallelWorkerReportLastRecEnd(XLogRecPtr last_xlog_end)
  *
  * Also explicitly detach from dsm segment so that subsystems using
  * on_dsm_detach() have a chance to send stats before the stats subsystem is
- * shut down as as part of a before_shmem_exit() hook.
+ * shut down as part of a before_shmem_exit() hook.
  *
  * One might think this could instead be solved by carefully ordering the
  * attaching to dsm segments, so that the pgstats segments get detached from

src/backend/catalog/heap.c

@@ -3547,7 +3547,7 @@ restart:
 		/*
 		 * If this constraint has a parent constraint which we have not seen
 		 * yet, keep track of it for the second loop, below.  Tracking parent
-		 * constraints allows us to climb up to the top-level level constraint
+		 * constraints allows us to climb up to the top-level constraint
 		 * and look for all possible relations referencing the partitioned
 		 * table.
 		 */

src/backend/commands/copyfromparse.c

@@ -37,7 +37,7 @@
  * the data is valid in the current encoding.
  *
  * In binary mode, the pipeline is much simpler.  Input is loaded into
- * into 'raw_buf', and encoding conversion is done in the datatype-specific
+ * 'raw_buf', and encoding conversion is done in the datatype-specific
  * receive functions, if required.  'input_buf' and 'line_buf' are not used,
  * but 'attribute_buf' is used as a temporary buffer to hold one attribute's
  * data when it's passed the receive function.

src/backend/partitioning/partdesc.c

@@ -91,7 +91,7 @@ RelationGetPartitionDesc(Relation rel, bool omit_detached)
 	 * cached descriptor too.  We determine that based on the pg_inherits.xmin
 	 * that was saved alongside that descriptor: if the xmin that was not in
 	 * progress for that active snapshot is also not in progress for the
-	 * current active snapshot, then we can use use it.  Otherwise build one
+	 * current active snapshot, then we can use it.  Otherwise build one
 	 * from scratch.
 	 */
 	if (omit_detached &&

src/backend/storage/buffer/bufmgr.c

@@ -666,7 +666,7 @@ ReadRecentBuffer(RelFileNode rnode, ForkNumber forkNum, BlockNumber blockNum,
 		{
 			/*
 			 * It's now safe to pin the buffer.  We can't pin first and ask
-			 * questions later, because because it might confuse code paths
+			 * questions later, because it might confuse code paths
 			 * like InvalidateBuffer() if we pinned a random non-matching
 			 * buffer.
 			 */

src/backend/storage/ipc/standby.c

@@ -130,7 +130,7 @@ InitRecoveryTransactionEnvironment(void)
  *
  * This must be called even in shutdown of startup process if transaction
  * tracking has been initialized. Otherwise some locks the tracked
- * transactions were holding will not be released and and may interfere with
+ * transactions were holding will not be released and may interfere with
  * the processes still running (but will exit soon later) at the exit of
  * startup process.
  */

src/include/access/tableam.h

@@ -157,7 +157,7 @@ typedef struct TM_FailureData
  * work, too.  This is a little like bottom-up deletion, but not too much.
  * The tableam will only perform speculative work when it's practically free
  * to do so in passing for simple deletion caller (while always performing
- * whatever work is is needed to enable knowndeletable/LP_DEAD index tuples to
+ * whatever work is needed to enable knowndeletable/LP_DEAD index tuples to
  * be deleted within index AM).  This is the real reason why it's possible for
  * simple index deletion caller to specify knowndeletable = false up front
  * (this means "check if it's possible for me to delete corresponding index