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/*! @page database_config Database Configuration
WiredTiger databases are configured using the ::wiredtiger_open call,
which takes a configuration string argument. In addition to this, the
database configuration can be specified using the \c WiredTiger.config
file or the WIREDTIGER_CONFIG environment variable.
When a WiredTiger database is created, the configuration string passed
to ::wiredtiger_open is saved to a WiredTiger home directory file named
\c WiredTiger.basecfg, and that configuration file is read whenever the
database is subsequently opened.
The configuration string to the ::wiredtiger_open call allows applications
to do per run settings (such as with or without statistics) or override
original creation settings. The user config file and the environment
variable allow system administrators to override application settings
without recompilation.
@section config_order Configuration ordering
When a database is created or opened, the order of configuration is:
- Any \c WiredTiger.basecfg file,
- which is overridden by the ::wiredtiger_open configuration string argument.
- which is overridden by the \c WiredTiger.config file,
- which is overridden by the \c WIREDTIGER_CONFIG environment variable,
@section config_env WIREDTIGER_CONFIG environment variable
If the \c WIREDTIGER_CONFIG environment variable is set, it is read as
a configuration string.
If the process is running with special privileges and \c WIREDTIGER_CONFIG
is set, the ::wiredtiger_open function must be configured with the
\c use_environment_priv flag, or the call to ::wiredtiger_open will fail.
See @ref home for more details.
@section config_file WiredTiger.config file
If a file named \c WiredTiger.config appears in the WiredTiger home
directory, it is read as a configuration string.
The file is minimally parsed in order to build configuration strings for
the WiredTiger configuration parser:
<ul>
<li>A backslash (<b><tt>\\</tt></b>) followed by any character other
than a newline character leaves both characters untouched; otherwise,
if a backslash is followed by a newline character, both the backslash
and the newline character are discarded.
<li>Any text between double-quote pairs (<b><tt>"</tt></b>) is left
untouched, including newline and white-space characters. Backslash
characters escape double-quote characters: a backslash escaped
double-quote character can neither start nor end a quoted string.
<li>Comments are discarded. If the first non-white-space character
following an unquoted and unescaped newline character is a hash mark
(<b><tt>#</tt></b>), all characters up to the next newline character are
discarded. The ending newline character cannot be escaped or quoted,
once a comment line is identified, all characters to the next newline
are simply discarded.
<li>Otherwise, all lines are concatenated and the newline characters
replaced with commas.
</ul>
@section config_base WiredTiger.basecfg file
When a WiredTiger database is created, non-default configuration
information specified to ::wiredtiger_open is saved to a WiredTiger home
directory file named \c WiredTiger.basecfg, and that configuration file
is read whenever the database is subsequently opened.
For example, if a shared library extensions are required, those settings
will be saved to the base configuration file so it's easier to write
general-purpose applications that might not be aware of how a particular
database was created and configured.
Users should not not edit this file, set the \c WIREDTIGER_CONFIG
environment variable or create a \c WiredTiger.config file instead, as
those settings override the settings in the base configuration file.
This file is a potential problem for applications that want to retain
the ability to downgrade to previous releases. If a new database is
created after an upgrade, the base configuration file might have
configuration strings that would cause a previous version of the
application to fail. For this reason, applications that may want to
downgrade should configure the ::wiredtiger_open value \c config_base
to \c false so the base configuration file is not written as part of
database create.
*/
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