Berkeley DB: Db::stat
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++

# Db::stat |

`

###

    #include <db_cxx.h>

    extern "C" {
    	typedef void *(*db_malloc_fcn_type)(size_t);
    };
    int
    Db::stat(void *sp, db_malloc_fcn_type db_malloc, u_int32_t flags);

# Description

The Db::stat method creates a statistical structure and copies a pointer to it into user-specified memory locations. Specifically, if sp is non-NULL, a pointer to the statistics for the database are copied into the memory location it references.

Statistical structures are created in allocated memory. If db_malloc is non-NULL, it is called to allocate the memory, otherwise, the library function malloc(3) is used. The function db_malloc must match the calling conventions of the malloc(3) library routine. Regardless, the caller is responsible for deallocating the returned memory. To deallocate returned memory, free the returned memory reference, references inside the returned memory do not need to be individually freed.

The flags parameter must be set to 0 or the following value:

DB_CACHED_COUNTS
  Return a cached count of the keys and records in a database. This flag makes it possible for applications to request an possibly approximate key and record count without incurring the performance penalty of traversing the entire database. The statistics information described for the access method XX_nkeys and XX_ndata fields below is filled in, but no other information is collected. If the cached information has never been set, the fields will be returned set to 0.

DB_RECORDCOUNT
  Return a count of the records in a Btree or Recno Access Method database. This flag makes it possible for applications to request a record count without incurring the performance penalty of traversing the entire database. The statistics information described for the bt_nkeys field below is filled in, but no other information is collected.

  This option is only available for Recno databases, or Btree databases where the underlying database was created with the DB_RECNUM flag.

The Db::stat method may access all of the pages in the database, incurring a severe performance penalty as well as possibly flushing the underlying buffer pool.

In the presence of multiple threads or processes accessing an active database, the information returned by Db::stat may be out-of-date.

If the database was not opened readonly and the DB_CACHED_COUNTS flag was not specified, the cached key and record numbers will be updated after the statistical information has been gathered.

The Db::stat method cannot be transaction protected. For this reason, it should be called in a thread of control that has no open cursors or active transactions.

The Db::stat method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success.

### Hash Statistics

In the case of a Hash database, the statistics are stored in a structure of type DB_HASH_STAT. The following fields will be filled in:

u_int32_t hash_magic;
  Magic number that identifies the file as a Hash file.
u_int32_t hash_version;
  The version of the Hash database.
u_int32_t hash_nkeys;
  The number of unique keys in the database.
u_int32_t hash_ndata;
  The number of key/data pairs in the database.]
u_int32_t hash_pagesize;
  The underlying Hash database page (and bucket) size.
u_int32_t hash_nelem;
  The estimated size of the hash table specified at database creation time.
u_int32_t hash_ffactor;
  The desired fill factor (number of items per bucket) specified at database creation time.
u_int32_t hash_buckets;
  The number of hash buckets.
u_int32_t hash_free;
  The number of pages on the free list.
u_int32_t hash_bfree;
  The number of bytes free on bucket pages.
u_int32_t hash_bigpages;
  The number of big key/data pages.
u_int32_t hash_big_bfree;
  The number of bytes free on big item pages.
u_int32_t hash_overflows;
  The number of overflow pages (overflow pages are pages that contain items that did not fit in the main bucket page).
u_int32_t hash_ovfl_free;
  The number of bytes free on overflow pages.
u_int32_t hash_dup;
  The number of duplicate pages.
u_int32_t hash_dup_free;
  The number of bytes free on duplicate pages.

### Btree and Recno Statistics

In the case of a Btree or Recno database, the statistics are stored in a structure of type DB_BTREE_STAT. The following fields will be filled in:

u_int32_t bt_magic;
  Magic number that identifies the file as a Btree database.
u_int32_t bt_version;
  The version of the Btree database.
u_int32_t bt_nkeys;
  For the Btree Access Method, the number of unique keys in the database.

  For the Recno Access Method, the number of records in the database.

u_int32_t bt_ndata;
  For the Btree Access Method, the number of key/data pairs in the database.

  For the Recno Access Method, the number of records in the database. If the database has been configured to not re-number records during deletion, the number of records will only reflect undeleted records.

u_int32_t bt_pagesize;
  Underlying database page size.
u_int32_t bt_minkey;
  The minimum keys per page.
u_int32_t bt_re_len;
  The length of fixed-length records.
u_int32_t bt_re_pad;
  The padding byte value for fixed-length records.
u_int32_t bt_levels;
  Number of levels in the database.
u_int32_t bt_int_pg;
  Number of database internal pages.
u_int32_t bt_leaf_pg;
  Number of database leaf pages.
u_int32_t bt_dup_pg;
  Number of database duplicate pages.
u_int32_t bt_over_pg;
  Number of database overflow pages.
u_int32_t bt_free;
  Number of pages on the free list.
u_int32_t bt_int_pgfree;
  Number of bytes free in database internal pages.
u_int32_t bt_leaf_pgfree;
  Number of bytes free in database leaf pages.
u_int32_t bt_dup_pgfree;
  Number of bytes free in database duplicate pages.
u_int32_t bt_over_pgfree;
  Number of bytes free in database overflow pages.

### Queue Statistics

In the case of a Queue database, the statistics are stored in a structure of type DB_QUEUE_STAT. The following fields will be filled in:

u_int32_t qs_magic;
  Magic number that identifies the file as a Queue file.
u_int32_t qs_version;
  The version of the Queue file type.
u_int32_t qs_nkeys;
  The number of records in the database.
u_int32_t qs_ndata;
  The number of records in the database.
u_int32_t qs_pagesize;
  Underlying database page size.
u_int32_t qs_pages;
  Number of pages in the database.
u_int32_t qs_re_len;
  The length of the records.
u_int32_t qs_re_pad;
  The padding byte value for the records.
u_int32_t qs_pgfree;
  Number of bytes free in database pages.
u_int32_t qs_start;
  Start offset.
u_int32_t qs_first_recno;
  First undeleted record in the database.
u_int32_t qs_cur_recno;
  Last allocated record number in the database.

The Db::stat method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success.

# Errors

The Db::stat method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the Db::stat method may fail and either return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

### Class

Db

# See Also

Db::close, Db::cursor, Db::del, Db::err, Db::fd, Db::get, Db::get_byteswapped, Db::get_type, Db::join, Db::key_range, Db::open, Db::put, Db::remove, Db::set_bt_compare, Db::set_bt_minkey, Db::set_bt_prefix, Db::set_cachesize, Db::set_dup_compare, Db::set_errcall, Db::set_errfile, Db::set_errpfx, Db::set_flags, Db::set_h_ffactor, Db::set_h_hash, Db::set_h_nelem, Db::set_lorder, Db::set_malloc, Db::set_pagesize, Db::set_paniccall, Db::set_q_extentsize, Db::set_realloc, Db::set_re_delim, Db::set_re_len, Db::set_re_pad, Db::set_re_source, Db::stat, Db::sync, Db::upgrade and Db::verify.`

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