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/*! @m_page{{c,java},config_strings,Configuration Strings}
@section config_intro Introduction
Methods in WiredTiger take a configuration string to provide optional
arguments and configure non-standard behaviors. These strings are
simple comma-separated lists of <code>"<key>=<value>"</code> pairs, and
all have the same format:
<pre>
[key['='value]][','[key['='value]]]*
</pre>
Keys and values and values that consist of alphanumeric characters can be
specified directly. More precisely, keys or values that match this regular
expression do not require quotes:
<pre>
[-_0-9A-Za-z./][^\\t\\r\\n :=,\\])}]*
</pre>
Configuration strings are case-sensitive (for example, "true" is a
valid boolean value, but "True" is not).
More complex keys and values can be specified by quoting them with double
quotes.
For example, a configuration string is used when opening a connection
to a database to specify if the database should be created and to set
the cache size:
@snippet ex_all.c Open a connection
Configuration strings are also used to configure the table schema. For
example, to create a table that uses C language strings for keys and
values:
@snippet ex_all.c Create a table
To handle more complex schema configuration, such as specifying multiple
columns in a table, values are nested using parentheses. For example:
@snippet ex_all.c Create a table with columns
All types of parentheses are treated equivalently by the parser.
When an integer values is expected, the value may have multiplier characters
appended, as follows:
<table>
@hrow{Character, Meaning, Change to value}
@row{\c B or \c b, byte, no change}
@row{\c K or \c k, kilobyte, multiply by 2^10}
@row{\c M or \c m, megabyte, multiply by 2^20}
@row{\c G or \c g, gigabyte, multiply by 2^30}
@row{\c T or \c t, terabyte, multiply by 2^40}
@row{\c P or \c p, petabyte, multiply by 2^50}
</table>
For example, the value \c 500B is the same as entering the number \c 500, the
value \c 500K is the same as \c 512000 and the string \c 500GB is the same as
\c 536870912000.
Values of type of "boolean" can be set to any of \c false, \c true, \c 0 or
\c 1. If no value is specified for a key, the value \c 1 is implied. For
example, all of the following forms of the \c overwrite configuration string
are identical:
@snippet ex_all.c boolean configuration string example
Configuration strings are processed in order from left to right, with
later settings overriding earlier ones (unless multiple settings for a
key are supported by the method).
Superfluous commas and whitespace in the configuration string are ignored
(including at the beginning and end of the string), so it is always safe to
combine two configuration strings by concatenating them with a comma in
between.
@m_if{c}
Empty configuration strings may be represented in C or C++ by passing
<code>NULL</code>.
@m_endif
@m_if{java}
Empty configuration strings may be represented in Java by passing
<code>null</code>.
@m_endif
@section config_json JavaScript Object Notation (JSON) compatibility
WiredTiger configuration strings are compatible with
<a href="http://www.json.org/">JavaScript Object Notation (JSON)</a>,
and will accept additional formatting as follows:
- parentheses may be round or square brackets or curly braces:
<code>'()'</code>, <code>'[]'</code> or <code>'{}'</code>
- the whole configuration string may optionally be wrapped in parentheses
- the key/value separator can be a colon: <code>':'</code>
- keys and values may be in double quotes: <code>"key" = "value"</code>
- quoted strings are interpreted as UTF-8 values
The result of this relaxed parsing is that applications may pass strings
representing valid <a href="http://json.org/">JSON objects</a> wherever
configuration strings are required.
For example, in Python, code might look as follows:
\code
import json
config = json.dumps({
"key_format" : "r",
"value_format" : "5sHQ",
"columns" : ("id", "country", "year", "population"),
"colgroup.population" : ["population"],
"index.country_year" : ["country", "year"]
})
\endcode
Because JSON compatibility allows colons to be used as key/value separators,
WiredTiger URIs may require quoting. For example, the following
WT_SESSION::checkpoint call specifies a set of URIs as checkpoint targets,
using double-quote characters to keep the parser from treating the colon
characters as JSON name/value separators:
@snippet ex_all.c JSON quoting example
*/
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