Read toast chunks in ascending order, looping if required

Toast chunks might be stored out-of-order in the table. We previously
ignored that and hoped for the best, but our toast.sql test actually
exhibits the problem on pre-14 servers where the 5th chunk of the last
test is small enough to fit into the first disk block.

Fix by looping over the table until all chunks have been read. A smarter
solution would require either toast index lookups or caching the chunks.

Close #20.

Author: Christoph Berg <[email protected]>
Debugging-By: Svetlana Derevyanko <[email protected]>

Author: df7cb

decode.c

@@ -1364,16 +1364,21 @@ ReadStringFromToast(const char *buffer,
 		varatt_external toast_ptr;
 		char	   *toast_data = NULL;
 		/* Number of chunks the TOAST data is divided into */
-		int32		num_chunks;
+		uint32		num_chunks;
+		/* Next chunk to read */
+		uint32		want_chunk_id = 0;
 		/* Actual size of external TOASTed value */
 		int32		toast_ext_size;
 		/* Path to directory with TOAST relation file */
 		char	   *toast_relation_path;
 		/* Filename of TOAST relation file */
 		char		toast_relation_filename[MAXPGPATH];
 		FILE	   *toast_rel_fp;
+		unsigned int toast_relation_block_size;
+		unsigned int toastDataRead = 0;
 		unsigned int block_options = 0;
 		unsigned int control_options = 0;
+		int			loops = 0;
 
 		VARATT_EXTERNAL_GET_POINTER(toast_ptr, buffer);
 
@@ -1383,7 +1388,7 @@ ReadStringFromToast(const char *buffer,
 #else
 		toast_ext_size = toast_ptr.va_extsize;
 #endif
-		num_chunks = (toast_ext_size - 1) / TOAST_MAX_CHUNK_SIZE + 1;
+		num_chunks = ((toast_ext_size - 1) / TOAST_MAX_CHUNK_SIZE) + 1;
 
 		printf("  TOAST value. Raw size: %8d, external size: %8d, "
 				"value id: %6d, toast relation id: %6d, chunks: %6d\n",
@@ -1399,46 +1404,63 @@ ReadStringFromToast(const char *buffer,
 		sprintf(toast_relation_filename, "%s/%d",
 				*toast_relation_path ? toast_relation_path : ".",
 				toast_ptr.va_toastrelid);
+		free(toast_relation_path);
 		toast_rel_fp = fopen(toast_relation_filename, "rb");
 		if (!toast_rel_fp) {
 			printf("Cannot open TOAST relation %s\n",
 					toast_relation_filename);
-			result = -1;
+			return -1;
 		}
-		else
+
+		toast_relation_block_size = GetBlockSize(toast_rel_fp);
+		toast_data = malloc(toast_ptr.va_rawsize);
+
+		/* Loop until all chunks have been read */
+		while (want_chunk_id < num_chunks)
 		{
-			unsigned int toast_relation_block_size = GetBlockSize(toast_rel_fp);
+			/* Restart at beginning of file */
 			fseek(toast_rel_fp, 0, SEEK_SET);
-			toast_data = malloc(toast_ptr.va_rawsize);
 
 			result = DumpFileContents(block_options,
-					control_options,
-					toast_rel_fp,
-					toast_relation_block_size,
-					-1, /* no start block */
-					-1, /* no end block */
-					true, /* is toast relation */
-					toast_ptr.va_valueid,
-					toast_ext_size,
-					toast_data);
-
-			if (result == 0)
-			{
-				if (VARATT_EXTERNAL_IS_COMPRESSED(toast_ptr))
-					result = DumpCompressedString(toast_data, toast_ext_size, parse_value);
-				else
-					result = parse_value(toast_data, toast_ext_size);
-			}
-			else
+						control_options,
+						toast_rel_fp,
+						toast_relation_block_size,
+						-1, /* no start block */
+						-1, /* no end block */
+						true, /* is toast relation */
+						toast_ptr.va_valueid,
+						&want_chunk_id,
+						toast_ext_size,
+						toast_data,
+						&toastDataRead);
+
+			if (loops++ > num_chunks)
 			{
-				printf("Error in TOAST file.\n");
+				printf("Not all TOAST chunks found after scanning TOAST table %" PRIu32 " times, giving up\n",
+						num_chunks);
+				result = -1;
 			}
 
-			free(toast_data);
-			fclose(toast_rel_fp);
+			if (result != 0)
+				break;
 		}
 
-		free(toast_relation_path);
+		fclose(toast_rel_fp);
+
+		if (result == 0)
+		{
+			if (VARATT_EXTERNAL_IS_COMPRESSED(toast_ptr))
+				result = DumpCompressedString(toast_data, toast_ext_size, parse_value);
+			else
+				result = parse_value(toast_data, toast_ext_size);
+		}
+		else
+		{
+			printf("Error in TOAST file.\n");
+		}
+
+		free(toast_data);
+
 	}
 	/* If tag is indirect or expanded, it was stored in memory. */
 	else
@@ -1516,6 +1538,7 @@ ToastChunkDecode(const char *tuple_data,
 		Oid toast_oid,
 		Oid *read_toast_oid,
 		uint32 *chunk_id,
+		uint32 *want_chunk_id,
 		char *chunk_data,
 		unsigned int *chunk_data_size)
 {
@@ -1561,6 +1584,10 @@ ToastChunkDecode(const char *tuple_data,
 		return;
 	}
 
+	/* Not the chunk we want to read next */
+	if (*chunk_id != *want_chunk_id)
+		return;
+
 	size -= processed_size;
 	data += processed_size;
 	if (size <= 0)
@@ -1587,4 +1614,7 @@ ToastChunkDecode(const char *tuple_data,
 				"Partial data: %s\n", size, copyString.data);
 		return;
 	}
+
+	/* advance to next chunk */
+	*want_chunk_id += 1;
 }

decode.h

@@ -21,6 +21,7 @@ ToastChunkDecode(const char* tuple_data,
 		Oid toast_oid,
 		Oid *read_toast_oid,
 		uint32 *chunk_id,
+		uint32 *want_chunk_id,
 		char *chunk_data,
 		unsigned int *chunk_data_size);
 

expected/toast_4.out

@@ -78,7 +78,7 @@ Block    0 ********************************************************
 <Header> -----
  Block Offset: 0x00000000         Offsets: Lower      52 (0x0034)
  Block: Size 8192  Version    4            Upper    7476 (0x1d34)
- LSN:  logid      . recoff 0x........      Special  8192 (0x2000)
+ LSN:  logid ...... recoff 0x........      Special  8192 (0x2000)
  Items:    7                      Free Space: 7424
  Checksum: 0x....  Prune XID: 0x00000000  Flags: 0x0004 (ALL_VISIBLE)
  Length (including item array): 52

pg_filedump.c

@@ -123,6 +123,7 @@ static void FormatBlock(unsigned int blockOptions,
 		unsigned int blockSize,
 		bool isToast,
 		Oid toastOid,
+		uint32 *want_chunk_id,
 		unsigned int toastExternalSize,
 		char *toastValue,
 		unsigned int *toastRead);
@@ -137,6 +138,7 @@ static void FormatItemBlock(char *buffer,
 		Page page,
 		bool isToast,
 		Oid toastOid,
+		uint32 *want_chunk_id,
 		unsigned int toastExternalSize,
 		char *toastValue,
 		unsigned int *toastRead);
@@ -1386,6 +1388,7 @@ FormatItemBlock(char *buffer,
 		Page page,
 		bool isToast,
 		Oid toastOid,
+		uint32 *want_chunk_id,
 		unsigned int toastExternalSize,
 		char *toastValue,
 		unsigned int *toastRead)
@@ -1557,13 +1560,19 @@ FormatItemBlock(char *buffer,
 					Oid read_toast_oid;
 
 					ToastChunkDecode(&buffer[itemOffset], itemSize, toastOid,
-									 &read_toast_oid, &chunkId, toastValue + *toastRead,
+									 &read_toast_oid, &chunkId, want_chunk_id, toastValue + *toastRead,
 									 &chunkSize);
 
 					if (verbose && read_toast_oid == toastOid)
-						printf("%s  Read TOAST chunk. TOAST Oid: %d, chunk id: %d, "
-							   "chunk data size: %d\n",
-							   indent, toastOid, chunkId, chunkSize);
+					{
+						if (chunkId == *want_chunk_id - 1) /* value already incremented */
+							printf("%s  Read TOAST chunk. TOAST Oid: %d, chunk id: %d, "
+								   "chunk data size: %d\n",
+								   indent, toastOid, chunkId, chunkSize);
+						else
+							printf("%s  Skipped out-of-order TOAST chunk. TOAST Oid: %d, chunk id: %d\n",
+								   indent, toastOid, chunkId);
+					}
 
 					*toastRead += chunkSize;
 
@@ -2096,6 +2105,7 @@ FormatBlock(unsigned int blockOptions,
 		unsigned int blockSize,
 		bool isToast,
 		Oid toastOid,
+		uint32 *want_chunk_id,
 		unsigned int toastExternalSize,
 		char *toastValue,
 		unsigned int *toastRead)
@@ -2132,6 +2142,7 @@ FormatBlock(unsigned int blockOptions,
 					page,
 					isToast,
 					toastOid,
+					want_chunk_id,
 					toastExternalSize,
 					toastValue,
 					toastRead);
@@ -2372,12 +2383,13 @@ DumpFileContents(unsigned int blockOptions,
 		int blockEnd,
 		bool isToast,
 		Oid toastOid,
+		uint32 *want_chunk_id,
 		unsigned int toastExternalSize,
-		char *toastValue)
+		char *toastValue,
+		unsigned int *toastDataRead)
 {
 	unsigned int	initialRead = 1;
 	unsigned int	contentsToDump = 1;
-	unsigned int	toastDataRead = 0;
 	BlockNumber		currentBlock = 0;
 	int				result = 0;
 	/* On a positive block size, allocate a local buffer to store
@@ -2419,7 +2431,7 @@ DumpFileContents(unsigned int blockOptions,
 			 * subsequent read gets the error. */
 			if (initialRead)
 				printf("Error: Premature end of file encountered.\n");
-			else if (!(blockOptions & BLOCK_BINARY))
+			else if (!(blockOptions & BLOCK_BINARY) && (!isToast || verbose))
 				printf("\n*** End of File Encountered. Last Block "
 					   "Read: %d ***\n", currentBlock - 1);
 
@@ -2445,9 +2457,10 @@ DumpFileContents(unsigned int blockOptions,
 							blockSize,
 							isToast,
 							toastOid,
+							want_chunk_id,
 							toastExternalSize,
 							toastValue,
-							&toastDataRead);
+							toastDataRead);
 				}
 			}
 		}
@@ -2468,7 +2481,7 @@ DumpFileContents(unsigned int blockOptions,
 		initialRead = 0;
 
 		/* If TOAST data is read */
-		if (isToast && toastDataRead >= toastExternalSize)
+		if (isToast && *toastDataRead >= toastExternalSize)
 			break;
 	}
 
@@ -2583,8 +2596,10 @@ main(int argv, char **argc)
 				blockEnd,
 				false /* is toast realtion */,
 				0,    /* no toast Oid */
+				NULL, /* no current TOAST chunk */
 				0,    /* no toast external size */
-				NULL  /* no out toast value */
+				NULL, /* no out toast value */
+				NULL  /* no toast value length */
 				);
 	}
 

pg_filedump.h

@@ -154,4 +154,4 @@ unsigned int GetBlockSize(FILE *fp);
 int DumpFileContents(unsigned int blockOptions, unsigned int controlOptions,
 					 FILE *fp, unsigned int blockSize, int blockStart,
 					int blockEnd, bool isToast, Oid toastOid,
-					unsigned int toastExternalSize, char *toastValue);
+					uint32 *want_chunk_id, unsigned int toastExternalSize, char *toastValue, unsigned int *toastDataRead);