db_stat not working correctly for Berkeley DB

Question

I downloaded Berkeley DB 5.3.28 and 18.1.40 from Oracle, compiled on Ubuntu 18.04 successfully. Everything worked as expected except db_stat utility doesn't want to return correct database statistics for me. Particularly, no of unique keys, no of data items, etc... are all wrong.

Here is my test code:

#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <db.h>


int main() {
  DB *dbp;
  DBT key, data;
  int ret, t_ret;

  ret = db_create(&dbp, NULL, 0);
    assert(ret == 0);

  ret = dbp->open(dbp, NULL, "sample.db", "", DB_BTREE, DB_CREATE, 0664);
  assert(ret == 0);

  memset(&key, 0, sizeof(key));
  memset(&data, 0, sizeof(data));
  key.data = (char*)"fruit";
  key.size = sizeof("fruit");
  data.data = (char*)"apple";
  data.size = sizeof("apple");

  ret = dbp->put(dbp, NULL, &key, &data, 0);
  assert(ret == 0);

  key.data = (char*)"color";
  key.size = sizeof("color");
  data.data = (char*)"red";
  data.size = sizeof("red");

  ret = dbp->put(dbp, NULL, &key, &data, 0);
  assert(ret == 0);

  key.data = (char*)"language";
  key.size = sizeof("language");
  data.data = (char*)"c";
  data.size = sizeof("c");

  ret = dbp->put(dbp, NULL, &key, &data, 0);
  assert(ret == 0);

  dbp->close(dbp, 0);
}

db_stat output:

db_stat -d sample.db

Sun Jun  7 20:26:59 2020    Local time
53162   Btree magic number
9   Btree version number
Little-endian   Byte order
multiple-databases  Flags
2   Minimum keys per-page
4096    Underlying database page size
1007    Overflow key/data size
1   Number of levels in the tree
1   Number of unique keys in the tree
1   Number of data items in the tree
0   Number of tree internal pages
0   Number of bytes free in tree internal pages (0% ff)
1   Number of tree leaf pages
4054    Number of bytes free in tree leaf pages (1% ff)
0   Number of tree duplicate pages
0   Number of bytes free in tree duplicate pages (0% ff)
0   Number of tree overflow pages
0   Number of bytes free in tree overflow pages (0% ff)
0   Number of empty pages
0   Number of pages on the free list

Answer 1

You named your database "" in the dbp->open call. So, you have to pass that to db_stat too, with the -s flag:

$ db_stat -d sample.db -s ""
Wed Jun 10 03:16:43 2020    Local time
53162   Btree magic number
9   Btree version number
Little-endian   Byte order
record-numbers, multiple-databases  Flags
2   Minimum keys per-page
8192    Underlying database page size
2031    Overflow key/data size
1   Number of levels in the tree
3   Number of unique keys in the tree
3   Number of data items in the tree
0   Number of tree internal pages
0   Number of bytes free in tree internal pages (0% ff)
1   Number of tree leaf pages
8090    Number of bytes free in tree leaf pages (1% ff)
0   Number of tree duplicate pages
0   Number of bytes free in tree duplicate pages (0% ff)
0   Number of tree overflow pages
0   Number of bytes free in tree overflow pages (0% ff)
0   Number of empty pages
0   Number of pages on the free list

(My BDB defaulted to an 8K page, but is otherwise the same.)