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<div class="textblock"><p>WiredTiger operations return a value of 0 on success and a non-zero value on error. Error codes may be either positive or negative: positive error codes are standard error codes as described for POSIX-like systems (for example, <code>EINVAL</code> or <code>EBUSY</code>), negative error codes are WiredTiger-specific (for example, <code>WT_ROLLBACK</code>).</p>
<p>WiredTiger-specific error codes always appear in the -31,800 to -31,999 range, inclusive.</p>
<p>WiredTiger returns <code>EBUSY</code> for operations requiring exclusive access, when an object is not available for exclusive access. For example, the <a class="el" href="struct_w_t___s_e_s_s_i_o_n.html#adf785ef53c16d9dcc77e22cc04c87b70" title="Drop (delete) an object. ">WT_SESSION::drop</a> or <a class="el" href="struct_w_t___s_e_s_s_i_o_n.html#a0334da4c85fe8af4197c9a7de27467d3" title="Verify a table or file. ">WT_SESSION::verify</a> methods will fail if the object has open cursors. Note that internal WiredTiger threads may temporarily open cursors on objects (for example, threads performing operations like statistics logging), and operations may temporarily fail and return <code>EBUSY</code> when there are no application cursors open on the object.</p>
<p>The following is a complete list of the WiredTiger-specific return values:</p>
<dl class="section user"><dt>WT_ROLLBACK</dt><dd>This error is generated when an operation cannot be completed due to a conflict with concurrent operations. The operation may be retried; if a transaction is in progress, it should be rolled back and the operation retried in a new transaction.</dd></dl>
<dl class="section user"><dt>WT_DUPLICATE_KEY</dt><dd>This error is generated when the application attempts to insert a record with the same key as an existing record without the 'overwrite' configuration to <a class="el" href="struct_w_t___s_e_s_s_i_o_n.html#afb5b4a69c2c5cafe411b2b04fdc1c75d" title="Open a new cursor on a data source or duplicate an existing cursor. ">WT_SESSION::open_cursor</a>.</dd></dl>
<dl class="section user"><dt>WT_ERROR</dt><dd>This error is returned when an error is not covered by a specific error return.</dd></dl>
<dl class="section user"><dt>WT_NOTFOUND</dt><dd>This error indicates an operation did not find a value to return. This includes cursor search and other operations where no record matched the cursor's search key such as <a class="el" href="struct_w_t___c_u_r_s_o_r.html#a444cdc0952e7f8d55d23173516c7037f" title="Update an existing record and optionally insert a record. ">WT_CURSOR::update</a> or <a class="el" href="struct_w_t___c_u_r_s_o_r.html#abbba24fe607fee519c4c9c4669cd4455" title="Remove a record. ">WT_CURSOR::remove</a>.</dd></dl>
<dl class="section user"><dt>WT_PANIC</dt><dd>This error indicates an underlying problem that requires a database restart. The application may exit immediately, no further WiredTiger calls are required (and further calls will themselves immediately fail).</dd></dl>
<dl class="section user"><dt>WT_RUN_RECOVERY</dt><dd>This error is generated when wiredtiger_open is configured to return an error if recovery is required to use the database.</dd></dl>
<dl class="section user"><dt>WT_CACHE_FULL</dt><dd>This error is only generated when wiredtiger_open is configured to run in-memory, and an insert or update operation requires more than the configured cache size to complete. The operation may be retried; if a transaction is in progress, it should be rolled back and the operation retried in a new transaction.</dd></dl>
<dl class="section user"><dt>WT_PREPARE_CONFLICT</dt><dd>This error is generated when the application attempts to update an already updated record which is in prepared state. An updated record will be in prepared state, when the transaction that performed the update is in prepared state.</dd></dl>
<dl class="section user"><dt>WT_TRY_SALVAGE</dt><dd>This error is generated when corruption is detected in an on-disk file. During normal operations, this may occur in rare circumstances as a result of a system crash. The application may choose to salvage the file or retry wiredtiger_open with the 'salvage=true' configuration setting.</dd></dl>
<h1><a class="anchor" id="error_translation"></a>
Translating errors</h1>
<p>The <a class="el" href="struct_w_t___s_e_s_s_i_o_n.html#abe03ccb716e097ed1bb4d42eb733c1f9" title="Return information about an error as a string. ">WT_SESSION::strerror</a> and <a class="el" href="group__wt.html#gae8bf720ddb4a7a7390b70424594c40fd" title="Return information about a WiredTiger error as a string (see WT_SESSION::strerror for a thread-safe A...">wiredtiger_strerror</a> functions return the standard text message associated with any WiredTiger, ISO C, or POSIX standard API.</p>
<div class="fragment"><div class="line"> <span class="keyword">const</span> <span class="keywordtype">char</span> *key = <span class="stringliteral">"non-existent key"</span>;</div><div class="line"> cursor->set_key(cursor, key);</div><div class="line"> <span class="keywordflow">if</span> ((ret = cursor->remove(cursor)) != 0) {</div><div class="line"> fprintf(stderr, <span class="stringliteral">"cursor.remove: %s\n"</span>, cursor->session->strerror(cursor->session, ret));</div><div class="line"> <span class="keywordflow">return</span> (ret);</div><div class="line"> }</div></div><!-- fragment --> <div class="fragment"><div class="line"> <span class="keyword">const</span> <span class="keywordtype">char</span> *key = <span class="stringliteral">"non-existent key"</span>;</div><div class="line"> cursor->set_key(cursor, key);</div><div class="line"> <span class="keywordflow">if</span> ((ret = cursor->remove(cursor)) != 0) {</div><div class="line"> fprintf(stderr, <span class="stringliteral">"cursor.remove: %s\n"</span>, <a class="code" href="group__wt.html#gae8bf720ddb4a7a7390b70424594c40fd">wiredtiger_strerror</a>(ret));</div><div class="line"> <span class="keywordflow">return</span> (ret);</div><div class="line"> }</div></div><!-- fragment --><p> Note that <a class="el" href="group__wt.html#gae8bf720ddb4a7a7390b70424594c40fd" title="Return information about a WiredTiger error as a string (see WT_SESSION::strerror for a thread-safe A...">wiredtiger_strerror</a> is not thread-safe.</p>
<h1><a class="anchor" id="event_message_handling"></a>
Message handling using the WT_EVENT_HANDLER</h1>
<p>Specific error and other message handling can be configured by passing an implementation of <a class="el" href="struct_w_t___e_v_e_n_t___h_a_n_d_l_e_r.html" title="The interface implemented by applications to handle error, informational and progress messages...">WT_EVENT_HANDLER</a> to <a class="el" href="group__wt.html#gacbe8d118f978f5bfc8ccb4c77c9e8813" title="Open a connection to a database. ">wiredtiger_open</a> or <a class="el" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html#adad5965cd4a60f65b5ac01f7ca6d1fc0" title="Open a session. ">WT_CONNECTION::open_session</a>.</p>
<p>For example, both informational and error messages might be passed to an application-specific logging function that added a timestamp and logged the message to a file, and error messages might additionally be output to the <code>stderr</code> file stream.</p>
<p>Additionally, applications will normally handle <code>WT_PANIC</code> as a special case. WiredTiger will always call the error handler callback with <code>WT_PANIC</code> in the case of a fatal error requiring database restart, however, WiredTiger cannot guarantee applications will see an application thread return <code>WT_PANIC</code> from a WiredTiger API call. For this reason, a correctly-written WiredTiger application will likely specify at least an error handler which will immediately exit or otherwise handle fatal errors. Note that no further WiredTiger calls are required after an error handler is called with <code>WT_PANIC</code> (and further calls will themselves immediately fail).</p>
<div class="fragment"><div class="line"><span class="comment">/*</span></div><div class="line"><span class="comment"> * Create our own event handler structure to allow us to pass context through to event handler</span></div><div class="line"><span class="comment"> * callbacks. For this to work the WiredTiger event handler must appear first in our custom event</span></div><div class="line"><span class="comment"> * handler structure.</span></div><div class="line"><span class="comment"> */</span></div><div class="line"><span class="keyword">typedef</span> <span class="keyword">struct </span>{</div><div class="line"> <a class="code" href="struct_w_t___e_v_e_n_t___h_a_n_d_l_e_r.html">WT_EVENT_HANDLER</a> h;</div><div class="line"> <span class="keyword">const</span> <span class="keywordtype">char</span> *app_id;</div><div class="line">} CUSTOM_EVENT_HANDLER;</div><div class="line"></div><div class="line"><span class="comment">/*</span></div><div class="line"><span class="comment"> * handle_wiredtiger_error --</span></div><div class="line"><span class="comment"> * Function to handle error callbacks from WiredTiger.</span></div><div class="line"><span class="comment"> */</span></div><div class="line"><span class="keywordtype">int</span></div><div class="line">handle_wiredtiger_error(</div><div class="line"> <a class="code" href="struct_w_t___e_v_e_n_t___h_a_n_d_l_e_r.html">WT_EVENT_HANDLER</a> *handler, <a class="code" href="struct_w_t___s_e_s_s_i_o_n.html">WT_SESSION</a> *session, <span class="keywordtype">int</span> error, <span class="keyword">const</span> <span class="keywordtype">char</span> *message)</div><div class="line">{</div><div class="line"> CUSTOM_EVENT_HANDLER *custom_handler;</div><div class="line"></div><div class="line"> <span class="comment">/* Cast the handler back to our custom handler. */</span></div><div class="line"> custom_handler = (CUSTOM_EVENT_HANDLER *)handler;</div><div class="line"></div><div class="line"> <span class="comment">/* Report the error on the console. */</span></div><div class="line"> fprintf(stderr, <span class="stringliteral">"app_id %s, thread context %p, error %d, message %s\n"</span>, custom_handler->app_id,</div><div class="line"> (<span class="keywordtype">void</span> *)session, error, message);</div><div class="line"></div><div class="line"> <span class="comment">/* Exit if the database has a fatal error. */</span></div><div class="line"> <span class="keywordflow">if</span> (error == <a class="code" href="group__wt.html#gaf4fc8744eb8fe4f1c6e125d0f2361992">WT_PANIC</a>)</div><div class="line"> exit(1);</div><div class="line"></div><div class="line"> <span class="keywordflow">return</span> (0);</div><div class="line">}</div><div class="line"></div><div class="line"><span class="comment">/*</span></div><div class="line"><span class="comment"> * handle_wiredtiger_message --</span></div><div class="line"><span class="comment"> * Function to handle message callbacks from WiredTiger.</span></div><div class="line"><span class="comment"> */</span></div><div class="line"><span class="keywordtype">int</span></div><div class="line">handle_wiredtiger_message(<a class="code" href="struct_w_t___e_v_e_n_t___h_a_n_d_l_e_r.html">WT_EVENT_HANDLER</a> *handler, <a class="code" href="struct_w_t___s_e_s_s_i_o_n.html">WT_SESSION</a> *session, <span class="keyword">const</span> <span class="keywordtype">char</span> *message)</div><div class="line">{</div><div class="line"> <span class="comment">/* Cast the handler back to our custom handler. */</span></div><div class="line"> printf(<span class="stringliteral">"app id %s, thread context %p, message %s\n"</span>, ((CUSTOM_EVENT_HANDLER *)handler)->app_id,</div><div class="line"> (<span class="keywordtype">void</span> *)session, message);</div><div class="line"></div><div class="line"> <span class="keywordflow">return</span> (0);</div><div class="line">}</div></div><!-- fragment --><div class="fragment"><div class="line"> CUSTOM_EVENT_HANDLER event_handler;</div><div class="line"></div><div class="line"> event_handler.h.handle_error = handle_wiredtiger_error;</div><div class="line"> event_handler.h.handle_message = handle_wiredtiger_message;</div><div class="line"> <span class="comment">/* Set handlers to NULL to use the default handler. */</span></div><div class="line"> event_handler.h.handle_progress = NULL;</div><div class="line"> event_handler.h.handle_close = NULL;</div><div class="line"> event_handler.app_id = <span class="stringliteral">"example_event_handler"</span>;</div><div class="line"></div><div class="line"> error_check(<a class="code" href="group__wt.html#gacbe8d118f978f5bfc8ccb4c77c9e8813">wiredtiger_open</a>(home, (<a class="code" href="struct_w_t___e_v_e_n_t___h_a_n_d_l_e_r.html">WT_EVENT_HANDLER</a> *)&event_handler, <span class="stringliteral">"create"</span>, &conn));</div></div><!-- fragment --></div></div><!-- contents -->
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