1MONGOC_CLIENT_SESSION_START_TRANSACTlIiMObONmN(oG3nO)gCo_cCLIENT_SESSION_START_TRANSACTION(3)
2
6 mongoc_client_session_start_transaction - mongoc_client_ses‐
7 sion_start_transaction()
8
10 bool
11 mongoc_client_session_start_transaction (mongoc_client_session_t *session,
12 const mongoc_transaction_opt_t *opts,
13 bson_error_t *error);
14 Start a multi-document transaction for all following operations in this
16 session. Any options provided in opts override options passed to mon‐
17 goc_session_opts_set_default_transaction_opts, and options inherited
18 from the mongoc_client_t. The opts argument is copied and can be freed
19 after calling this function.
20 The transaction must be completed with mongoc_client_session_com‐
22 mit_transaction or mongoc_client_session_abort_transaction. An
23 in-progress transaction is automatically aborted by mongoc_client_ses‐
24 sion_destroy.
25
27 • session: A mongoc_client_session_t.
28 • opts: A mongoc_transaction_opt_t or NULL.
30 • error: An optional location for a bson_error_t or NULL.
32
34 Returns true if the transaction was started. Returns false and sets er‐
35 ror if there are invalid arguments, such as a session with a transac‐
36 tion already in progress.
37
39 The following example demonstrates how to use error labels to reliably
40 execute a multi-document transaction despite network errors and other
41 transient failures.
42 example-transaction.c
44 /* gcc example-transaction.c -o example-transaction \
46 * $(pkg-config --cflags --libs libmongoc-1.0) */
47 /* ./example-transaction [CONNECTION_STRING] */
49 #include <stdio.h>
51 #include <mongoc/mongoc.h>
52 int
55 main (int argc, char *argv[])
56 {
57 int exit_code = EXIT_FAILURE;
58 mongoc_client_t *client = NULL;
60 mongoc_database_t *database = NULL;
61 mongoc_collection_t *collection = NULL;
62 mongoc_client_session_t *session = NULL;
63 mongoc_session_opt_t *session_opts = NULL;
64 mongoc_transaction_opt_t *default_txn_opts = NULL;
65 mongoc_transaction_opt_t *txn_opts = NULL;
66 mongoc_read_concern_t *read_concern = NULL;
67 mongoc_write_concern_t *write_concern = NULL;
68 const char *uri_string = "mongodb://127.0.0.1/?appname=transaction-example";
69 mongoc_uri_t *uri;
70 bson_error_t error;
71 bson_t *doc = NULL;
72 bson_t *insert_opts = NULL;
73 int32_t i;
74 int64_t start;
75 bson_t reply = BSON_INITIALIZER;
76 char *reply_json;
77 bool r;
78 mongoc_init ();
80 if (argc > 1) {
82 uri_string = argv[1];
83 }
84 uri = mongoc_uri_new_with_error (uri_string, &error);
86 if (!uri) {
87 MONGOC_ERROR ("failed to parse URI: %s\n"
88 "error message: %s\n",
89 uri_string,
90 error.message);
91 goto done;
92 }
93 client = mongoc_client_new_from_uri (uri);
95 if (!client) {
96 goto done;
97 }
98 mongoc_client_set_error_api (client, 2);
100 database = mongoc_client_get_database (client, "example-transaction");
101 /* inserting into a nonexistent collection normally creates it, but a
103 * collection can't be created in a transaction; create it now */
104 collection =
105 mongoc_database_create_collection (database, "collection", NULL, &error);
106 if (!collection) {
108 /* code 48 is NamespaceExists, see error_codes.err in mongodb source */
109 if (error.code == 48) {
110 collection = mongoc_database_get_collection (database, "collection");
111 } else {
112 MONGOC_ERROR ("Failed to create collection: %s", error.message);
113 goto done;
114 }
115 }
116 /* a transaction's read preferences, read concern, and write concern can be
118 * set on the client, on the default transaction options, or when starting
119 * the transaction. for the sake of this example, set read concern on the
120 * default transaction options. */
121 default_txn_opts = mongoc_transaction_opts_new ();
122 read_concern = mongoc_read_concern_new ();
123 mongoc_read_concern_set_level (read_concern, "snapshot");
124 mongoc_transaction_opts_set_read_concern (default_txn_opts, read_concern);
125 session_opts = mongoc_session_opts_new ();
126 mongoc_session_opts_set_default_transaction_opts (session_opts,
127 default_txn_opts);
128 session = mongoc_client_start_session (client, session_opts, &error);
130 if (!session) {
131 MONGOC_ERROR ("Failed to start session: %s", error.message);
132 goto done;
133 }
134 /* in this example, set write concern when starting the transaction */
136 txn_opts = mongoc_transaction_opts_new ();
137 write_concern = mongoc_write_concern_new ();
138 mongoc_write_concern_set_wmajority (write_concern, 1000 /* wtimeout */);
139 mongoc_transaction_opts_set_write_concern (txn_opts, write_concern);
140 insert_opts = bson_new ();
142 if (!mongoc_client_session_append (session, insert_opts, &error)) {
143 MONGOC_ERROR ("Could not add session to opts: %s", error.message);
144 goto done;
145 }
146 retry_transaction:
148 r = mongoc_client_session_start_transaction (session, txn_opts, &error);
149 if (!r) {
150 MONGOC_ERROR ("Failed to start transaction: %s", error.message);
151 goto done;
152 }
153 /* insert two documents - on error, retry the whole transaction */
155 for (i = 0; i < 2; i++) {
156 doc = BCON_NEW ("_id", BCON_INT32 (i));
157 bson_destroy (&reply);
158 r = mongoc_collection_insert_one (
159 collection, doc, insert_opts, &reply, &error);
160 bson_destroy (doc);
162 if (!r) {
164 MONGOC_ERROR ("Insert failed: %s", error.message);
165 mongoc_client_session_abort_transaction (session, NULL);
166 /* a network error, primary failover, or other temporary error in a
168 * transaction includes {"errorLabels": ["TransientTransactionError"]},
169 * meaning that trying the entire transaction again may succeed
170 */
171 if (mongoc_error_has_label (&reply, "TransientTransactionError")) {
172 goto retry_transaction;
173 }
174 goto done;
176 }
177 reply_json = bson_as_json (&reply, NULL);
179 printf ("%s\n", reply_json);
180 bson_free (reply_json);
181 }
182 /* in case of transient errors, retry for 5 seconds to commit transaction */
184 start = bson_get_monotonic_time ();
185 while (bson_get_monotonic_time () - start < 5 * 1000 * 1000) {
186 bson_destroy (&reply);
187 r = mongoc_client_session_commit_transaction (session, &reply, &error);
188 if (r) {
189 /* success */
190 break;
191 } else {
192 MONGOC_ERROR ("Warning: commit failed: %s", error.message);
193 if (mongoc_error_has_label (&reply, "TransientTransactionError")) {
194 goto retry_transaction;
195 } else if (mongoc_error_has_label (&reply,
196 "UnknownTransactionCommitResult")) {
197 /* try again to commit */
198 continue;
199 }
200 /* unrecoverable error trying to commit */
202 break;
203 }
204 }
205 exit_code = EXIT_SUCCESS;
207 done:
209 bson_destroy (&reply);
210 bson_destroy (insert_opts);
211 mongoc_write_concern_destroy (write_concern);
212 mongoc_read_concern_destroy (read_concern);
213 mongoc_transaction_opts_destroy (txn_opts);
214 mongoc_transaction_opts_destroy (default_txn_opts);
215 mongoc_client_session_destroy (session);
216 mongoc_collection_destroy (collection);
217 mongoc_database_destroy (database);
218 mongoc_uri_destroy (uri);
219 mongoc_client_destroy (client);
220 mongoc_cleanup ();
222 return exit_code;
224 }
225
228 MongoDB, Inc
229
231 2017-present, MongoDB, Inc
2321.20.0 NovM1O8N,GO2C0_2C1LIENT_SESSION_START_TRANSACTION(3)