Fix parallel index scan hang with deleted or half-dead pages.

robertmhaas · robertmhaas · commit 884a60840cd6 · 2017-12-13T16:15:44.000-05:00
The previous coding forgot to release the scan before seizing it again, leading to a lockup. Report by Patrick Hemmer. Diagnosis by Thomas Munro. Patch by Amit Kapila. Discussion: http://postgr.es/m/CAEepm=2xZUcOGP9V0O_G0=2P2wwXwPrkF=upWTCJSisUxMnuSg@mail.gmail.com
diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
@@ -1486,6 +1486,11 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, ScanDirection dir)
 				if (_bt_readpage(scan, dir, P_FIRSTDATAKEY(opaque)))
 					break;
 			}
+			else if (scan->parallel_scan != NULL)
+			{
+				/* allow next page be processed by parallel worker */
+				_bt_parallel_release(scan, opaque->btpo_next);
+			}
 
 			/* nope, keep going */
 			if (scan->parallel_scan != NULL)
@@ -1581,6 +1586,11 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, ScanDirection dir)
 				if (_bt_readpage(scan, dir, PageGetMaxOffsetNumber(page)))
 					break;
 			}
+			else if (scan->parallel_scan != NULL)
+			{
+				/* allow next page be processed by parallel worker */
+				_bt_parallel_release(scan, BufferGetBlockNumber(so->currPos.buf));
+			}
 
 			/*
 			 * For parallel scans, get the last page scanned as it is quite
