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/*! @class doc_cursor_types
The following are the builtin basic cursor types:
<table>
@hrow{URI, Type, Notes}
@row{<tt>table:\<table name\>[\<projection\>]</tt>,
table cursor,
table key\, table value(s) with optional projection of columns}
@row{<tt>colgroup:\<table name\>:\<column group name\></tt>,
column group cursor,
table key\, column group value(s)}
@row{<tt>index:\<table name\>:\<index name\>[\<projection\>]</tt>,
index cursor,
key=index key\, value=table value(s) with optional projection
of columns}
@row{<tt>join:table:\<table name\>[\<projection\>]</tt>,
join cursor,
key=table key\, value=table value(s) with optional projection
of columns}
</table>
Some administrative tasks can be accomplished using the following special
cursor types that give access to data managed by WiredTiger:
<table>
@hrow{URI, Type, Notes}
@row{<tt>backup:</tt>,
backup cursor,
key=<code>string</code>\, see @ref backup for details}
@row{<code>log:</code>,
log cursor,
key=<code>(long fileID\, long offset\, int seqno)</code>\,<br>
value=<code>(uint64_t txnid\, uint32_t rectype\,<br>
uint32_t optype\, uint32_t fileid\,<br>
WT_ITEM key\, WT_ITEM value)</code>\,<br>
see @ref cursor_log for details}
@row{<tt>metadata:[create]</tt>,
metadata cursor (optionally only returning configuration strings for
WT_SESSION::create if <code>create</code> is appended,
key=<code>string</code>\, value=<code>string</code>\,<br>
see @ref metadata for details}
@row{<tt>statistics:[\<data source URI\>]</tt>,
database or data source statistics cursor,
key=<code>int id</code>\,<br>
value=<code>(string description\,
string value\, uint64_t value)</code>\,<br>
see @ref data_statistics for details}
</table>
Advanced applications may also open the following low-level cursor types:
<table>
@hrow{URI, Type, Notes}
@row{<tt>file:\<file name\></tt>,
file cursor,
file key\, file value(s)}
@row{<tt>lsm:\<name\></tt>,
LSM cursor (key=LSM key\, value=LSM value), LSM key\, LSM value\,<br>
see @ref lsm}
</table>
*/
/* ----------------- */
/*! @m_page{{c,java},data_sources,Data Sources}
WiredTiger provides access to data from a variety of sources. At the
lowest level, data may be stored in a file using a tree structure. A
relational schema supporting tables, indices and column groups is
layered on top of file. Additional sources include LSM trees and
statistics, and applications can further extend the supported types by
implementing the ::WT_DATA_SOURCE interface.
Common operations on all data sources are performed using WT_CURSOR
handles. See @ref cursor_ops for a description of how to use
cursors.
@section data_builtin Builtin data sources
@copydoc doc_cursor_types
@subsection data_files Raw Files
WiredTiger's schema layer can be bypassed by opening cursors with a \c
"file:" URI, using the name of the underlying file. This can be useful for
seeing the contents of a column group or index without reading all of the
columns from the table.
For example, if an index becomes inconsistent with its primary, a file
cursor can read from the index without errors (even though some of the keys
that are returned may not exist in the primary).
@subsection data_indices Table Index data
When an index is created for a table, records are inserted into the index
whenever the table is updated. These records use a different key to the
primary table, as specified when the index is created with the
WT_SESSION::create method.
A cursor opened on an index has the specified index columns as its key,
accessed by WT_CURSOR::set_key and WT_CURSOR::get_key. The value columns
default to returning the value columns from the table, but this can be
overridden by configuring a projection cursor (see @ref cursor_projections),
which can access the table key columns or a subset of the value columns.
@subsection data_statistics Statistics Data
Statistics cursors can be used to retrieve run-time statistics about a
WiredTiger database as well as statistics for individual data sources.
The statistics are at two levels: per-database and per-individual data
source. Database-wide statistics are retrieved with the \c "statistics:"
URI; individual data source statistics are available by specifying
\c "statistics:<data source URI>".
The statistic key is an integer from the list of keys in
@ref_single statistics_keys "Statistics Keys". Statistics cursors return
three values from the WT_CURSOR::get_value call: a printable description of
the statistic, a printable version of the entry's value, and the entry's
unsigned 64-bit integral value, respectively.
The cursor's statistics values are loaded when the cursor is opened and
remain unchanged for the life of the cursor, unless the cursor is reset
by calling the WT_CURSOR::reset method, which reloads the values.
The following is an example of printing run-time statistics about the
WiredTiger engine:
@snippet ex_stat.c statistics database function
The following is an example of printing statistics about a table:
@snippet ex_stat.c statistics table function
Both examples can use a common display routine that iterates through the
statistics until the cursor returns the end of the list.
@snippet ex_stat.c statistics display function
Individual statistics values can be retrieved by searching for the
corresponding key, as shown in the following example:
@snippet ex_stat.c statistics retrieve by key
See @ref_single tune_statistics for more examples of how statistics can be
used.
*/
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