Re: backup manifests - Mailing list pgsql-hackers

On Wed, Nov 20, 2019 at 11:05 AM Suraj Kharage <suraj.kharage@enterprisedb.com> wrote:

Hi,

Since now we are generating the backup manifest file with each backup, it provides us an option to validate the given backup.  
Let's say, we have taken a backup and after a few days, we want to check whether that backup is validated or corruption-free without restarting the server.

Please find attached POC patch for same which will be based on the latest backup manifest patch from Rushabh. With this functionality, we add new option to pg_basebackup, something like --verify-backup.
So, the syntax would be:
./bin/pg_basebackup --verify-backup -D <backup_directory_path>

Basically, we read the backup_manifest file line by line from the given directory path and build the hash table, then scan the directory and compare each file with the hash entry.

Thoughts/suggestions?

I like the idea of verifying the backup once we have backup_manifest with us.
Periodically verifying the already taken backup with this simple tool becomes
easy now.

I have reviewed this patch and here are my comments:

1.
@@ -30,7 +30,9 @@
 #include "common/file_perm.h"
 #include "common/file_utils.h"
 #include "common/logging.h"
+#include "common/sha2.h"
 #include "common/string.h"
+#include "fe_utils/simple_list.h"
 #include "fe_utils/recovery_gen.h"
 #include "fe_utils/string_utils.h"
 #include "getopt_long.h"
@@ -38,12 +40,19 @@
 #include "pgtar.h"
 #include "pgtime.h"
 #include "pqexpbuffer.h"
+#include "pgrhash.h"
 #include "receivelog.h"
 #include "replication/basebackup.h"
 #include "streamutil.h"

Please add new files in order.

2.
Can hash related file names be renamed to backuphash.c and backuphash.h?

3.
Need indentation adjustments at various places.

4.
+            char        buf[1000000];  // 1MB chunk

It will be good if we have multiple of block /page size (or at-least power of 2
number).

5.
+typedef struct pgrhash_entry
+{
+    struct pgrhash_entry *next; /* link to next entry in same bucket */
+    DataDirectoryFileInfo *record;
+} pgrhash_entry;
+
+struct pgrhash
+{
+    unsigned    nbuckets;        /* number of buckets */
+    pgrhash_entry **bucket;        /* pointer to hash entries */
+};
+
+typedef struct pgrhash pgrhash;

These two can be moved to .h file instead of redefining over there.

6.
+/*
+ * TODO: this function is not necessary, can be removed.
+ * Test whether the given row number is match for the supplied keys.
+ */
+static bool
+pgrhash_compare(char *bt_filename, char *filename)

Yeah, it can be removed by doing strcmp() at the required places rather than
doing it in a separate function.

7.
mdate is not compared anywhere. I understand that it can't be compared with
the file in the backup directory and its entry in the manifest as manifest
entry gives mtime from server file whereas the same file in the backup will
have different mtime. But adding a few comments there will be good.

8.
+    char        mdate[24];

should be mtime instead?


Thanks

--

Jeevan Chalke
Associate Database Architect & Team Lead, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company