11. Berkeley DB Data Store and Concurrent Data Store Applications - Quick Start Guide - 《Oracle Berkeley DB Programmer's Reference Guide （Version 18.1.32）》

Quick Start Guide

Quick Start Guide

Here is an example program for creating/configuring a Berkeley DB environment (using Data Store, Concurrent Data Store and Transactional Data Store environments):

int
main(argc, argv)
    int argc;
    char *argv[];
{
    DB_ENV *dbenv, *rm;
    DB *db;
    DBC *dbc;
    DB_TXN *txn;
    const char *home = ".";

Data Store Environment

Create a Data Store object and configure it.
```
db_env_create(&dbenv, 0);
```

Set the cache size.

dbenv->set_cachesize(dbenv, 0, 64 * 1024, 0);

Open the environment. The only flag required is DB_INIT_MPOOL.

dbenv->open(dbenv, home, DB_INIT_MPOOL | DB_CREATE, 0644);

Create the database handle.
```
db_create(&db, dbenv, 0);
```

Open the database, no flags are required.

db->open(db, NULL, NULL, "database", DB_BTREE, DB_CREATE, 0644);

Begin a cursor.
```
db->cursor(db, NULL, &dbc, 0);
```

Close the cursor.

dbc->close(dbc);
db->close(db, 0);
dbenv->close(dbenv, 0);

Concurrent Data Store Environment

Create a Concurrent Data Store environment object and configure it.
```
db_env_create(&dbenv, 0);
```

Set the cache size.

dbenv->set_cachesize(dbenv, 0, 64 * 1024, 0);

Open the environment. The environment requires the DB_INIT_CDB and DB_INIT_MPOOL flags.
```
dbenv->open(dbenv, home, DB_INIT_CDB | DB_INIT_MPOOL | DB_CREATE, 0644);
```
Create the database handle.
```
db_create(&db, dbenv, 0);
```
Begin a Concurrent Data Store transaction.
```
dbenv->cdsgroup_begin(dbenv, &txn);
```

Open the database. A Concurrent Data Store transaction is required.

db->open(db, txn, NULL, "database", DB_BTREE, DB_CREATE, 0644);

Begin a cursor. A transaction and the DB_WRITECURSOR flag is required if the cursor will insert values.
```
db->cursor(db, txn, &dbc, DB_WRITECURSOR);
```
Close the cursor.
```
dbc->close(dbc);
```

Commit the transaction.

txn->commit(txn, 0);
db->close(db, 0);
dbenv->close(dbenv, 0);

Transactional Data Store Environment

Create a Transactional environment object and configure it.
```
db_env_create(&dbenv, 0);
```

Set the cache size.

dbenv->set_cachesize(dbenv, 0, 64 * 1024, 0);

Open the environment. The TDB_INIT_LOCK, DB_INIT_LOG, DB_INIT_MPOOL, DB_INIT_TXN flags required by it specify that the environment will have transactional support.
```
dbenv->open(dbenv, home, 
TDB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL | 
DB_INIT_TXN | DB_CREATE, 0644);
```
Create the database handle.
```
db_create(&db, dbenv, 0);
```
Open the database with the DB_AUTO_COMMIT flag. For a database to support transactions it has to be open with either the DB_AUTO_COMMIT flag, or a transaction.
```
db->open(db, NULL, NULL, "database", DB_BTREE, 
DB_AUTO_COMMIT | DB_CREATE, 0644);
```
Begin a transaction.
```
dbenv->txn_begin(dbenv, NULL, &txn, 0);
```
Begin a transactional cursor.
```
db->cursor(db, txn, &dbc, 0);
```
Close the cursor.
```
dbc->close(dbc);
```

Commit and close the transaction.

txn->commit(txn, 0);
db->close(db, 0);
dbenv->close(dbenv, 0);