reread-v2.patch

diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index 9f735a2c07..fe7285f7a2 100644
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -1258,6 +1258,7 @@ sendFile(const char *readfilename, const char *tarfilename, struct stat *statbuf
 	int			i;
 	pgoff_t		len = 0;
 	char		page[BLCKSZ];
+	bool		block_retry = false;
 	size_t		pad;
 	PageHeader  phdr;
 	int			segmentno = 0;
@@ -1341,6 +1342,50 @@ sendFile(const char *readfilename, const char *tarfilename, struct stat *statbuf
 					phdr = (PageHeader) page;
 					if (phdr->pd_checksum != checksum)
 					{
+						/*
+						 * Retry the block on the first failure.  It's possible
+						 * that we read the first 4K page of the block just
+						 * before postgres updated the entire block so it ends
+						 * up looking torn to us.  We only need to retry once
+						 * because the LSN should be updated to something we can
+						 * ignore on the next pass.  If the error happens again
+						 * then it is a true validation failure.
+						 */
+						if (block_retry == false)
+						{
+							/* Reread the failed block */
+							if (fseek(fp, -(cnt - BLCKSZ * i), SEEK_CUR) == -1)
+							{
+								ereport(ERROR,
+										(errcode_for_file_access(),
+										 errmsg("could not fseek in file \"%s\": %m",
+										 readfilename)));
+							}
+
+							if (fread(buf + BLCKSZ * i, 1, BLCKSZ, fp) != BLCKSZ)
+							{
+								ereport(ERROR,
+										(errcode_for_file_access(),
+										 errmsg("could not reread block %d of file \"%s\": %m",
+										 blkno, readfilename)));
+							}
+
+							if (fseek(fp, cnt - BLCKSZ * i - BLCKSZ, SEEK_CUR) == -1)
+							{
+								ereport(ERROR,
+										(errcode_for_file_access(),
+										 errmsg("could not fseek in file \"%s\": %m",
+										 readfilename)));
+							}
+
+							/* Set flag so we know a retry was attempted */
+							block_retry = true;
+
+							/* Reset loop to validate the block again */
+							i--;
+							continue;
+						}
+
 						ereport(WARNING,
 								(errmsg("checksum verification failed in file "
 										"\"%s\", block %d: calculated %X but "
@@ -1350,6 +1395,7 @@ sendFile(const char *readfilename, const char *tarfilename, struct stat *statbuf
 						checksum_failure = true;
 					}
 				}
+				block_retry = false;
 				blkno++;
 			}
 		}