### db_codegen

`

###

    db_codegen [-Vv] [-a c] [-i file] [-o file]

### Description

The db_codegen utility generates application code to create and configure Berkeley DB database environments and databases based on a simple description language, and writes it to one or more output files. The generated code may need modification, in the case of complicated applications, but will usually significantly reduce the time required to create Berkeley DB applications.

The options are as follows:

-a
  Generate code for the specified API (currently, only "c" is accepted).
-i
  Specify an input file; by default, stdin is used.
-o
  Specify an output file prefix; by default, "application" is used.
-V
  Write the library version number to the standard output, and exit.
-v
  Run in verbose mode.

The db_codegen utility exits 0 on success, and >0 if an error occurs.

### C Language Specific Information

By default, when the db_codegen utility generates C-language code, the output file is named "application.c". The output filename can be specified with -o option.

At the beginning of the output file is a list of public database environment (DB_ENV) handles and database (DB) handles, as specified by the description language. The database environment handle variables are named "XXX_dbenv", where "XXX" is the name of the environment in the input specification. For databases associated with a database environment, the database handle variables are named "XXX_YYY", where "XXX" is the name of the environment, and "YYY" is the name of the database. For standalone databases, the database handle variables are named "XXX", where "XXX" is the name of the database.

There are two public functions in the output file: bdb_startup and bdb_shutdown. The bdb_startup function should be called to create and configure the database environments and databases, and the bdb_shutdown function should be called to gracefully shut down the environments and databases.

### Specification Language

The db_codegen uses a simple description language:

- Lines in the input consist of white-space separated tokens.
- Tokens are case-insensitive.
- Empty lines, and lines where the first non-space character is hash mark ("#"). are ignored. In addition, hash marks may appear in lines, in which case the content of the line from the hash mark to the end of the line is ignored.

There are two top-level objects: "environment" and "database", which correspond to database environments and databases, respectively. These top-level objects can be associated with keywords to describe their configuration and relationships.

For example, the following input would create two standalone databases:

>     database data_one {
>         type btree
>     }
>     database data_two {
>         type btree
>     }

In this case, there would be no DB_ENV handle, and the public DB handles would be:

>     DB      *data_one;
>     DB      *data_two;

For example, the following input would create a database environment which contains three databases:

>     environment myenv {
>         database data_one {
>     	type btree
>         }
>         database data_two {
>         	type btree
>         }
>         database data_three {
>         	type btree
>         }
>     }

In this case, the public DB_ENV and DB handles would be:

>     DB_ENV  *myenv_dbenv;
>     DB      *myenv_data_one;
>     DB      *myenv_data_two;
>     DB      *myenv_data_three;

A variety of keywords can be specified for the databases and the environments. For example, the cache size can be specified for the database environment, and the page size can be specified for the database, as well as secondary relationships:

>     environment myenv {
>         cachesize 2 0 10
>         database data_one {
>         	type btree
>         	pagesize 1024
>         }
>         database data_two {
>     	primary data_one
>     	secondary_offset 10 15
>         	type btree
>         	pagesize 32768
>         }
>         database data_three {
>         	type btree
>         	pagesize 512
>         }
>     }

### Environment Keywords

environment
  Start a database environment block.

  There must be three tokens on the line: the keyword, the name of the environment and an opening brace ("{").

home
  Specify the database environment home directory.

  There must be two tokens on the line: the keyword, and the home directory.

cachesize
  Specify the database environment cache size.

  There must be two tokens on the line: the keyword, the gigabytes of cache, the bytes of cache, and the number of caches (the number of underlying physical areas into which the cache is logically divided).

private
  Specify the database environment is private.

  There must be one token on the line: the keyword by itself.

}
  End the database environment block.

  There must be one token on the line: the keyword by itself.

### Database Keywords

database
  Start a database block.

  There must be three tokens on the line: the keyword, the name of the database and an opening brace ("{").

custom
  Specify a custom key-comparison routine. This is used when the Btree database requires a specific sort that db_codegen cannot generate. A stub key comparison routine will be created and configured for the database which should be modified as necessary. See the "key_type" keyword for more information.

  There must be one token on the line: the keyword by itself.

dupsort
  Configure the database to support sorted duplicates.

  There must be one token on the line: the keyword by itself.

extentsize
  Configure the size of the Queue database extent files.

  There must be two tokens on the line: the keyword, and the extent file size, as a number of pages.

key_type
  Configure a integral type key-comparison routine. This is used when the Btree database Btree database key is an integral type (such as "unsigned int", or "u_int32_t"). Any C-language integral type may be specified. See the "custom" keyword for more information. A Btree comparison routine based on the type of the key will be created and configured.

  There must be two tokens on the line: the keyword, and the type.

pagesize
  Configure the database page size.

  There must be two tokens on the line: the keyword, and the page size in bytes.

primary
  Configure the database as a secondary index. A stub secondary callback routine will be created and configured for the database, which should be modified as necessary. See the "secondary_offset" keyword for more information.

  name of the primary database for which this database is a secondary.

recnum
  Configure the Btree database to support record number access.

  There must be one token on the line: the keyword by itself.

re_len
  Configure the record length for a Queue database or a fixed-length Recno database.

  There must be two tokens on the line: the keyword, and the length of a record, in bytes.

secondary_offset
  Configure a secondary callback routine based on a byte string found in the primary database's data item.

  There must be three tokens on the line: the keyword, the byte offset from the beginning of the primary data item where the secondary key occurs, and the length of the secondary key in bytes.

transaction
  Configure the database (and, by extension, the database environment), to be transactional.

  There must be one token on the line: the keyword by itself.

type
  Configure the database type.

  There must be two tokens on the line: the keyword, and the type, where the type is one of "btree", "hash", "queue" or "recno".

}
  End the database environment block.

  There must be one token on the line: the keyword by itself.

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