1<!-- doc/src/sgml/event-trigger.sgml --> 2 3 <chapter id="event-triggers"> 4 <title>Event Triggers</title> 5 6 <indexterm zone="event-triggers"> 7 <primary>event trigger</primary> 8 </indexterm> 9 10 <para> 11 To supplement the trigger mechanism discussed in <xref linkend="triggers"/>, 12 <productname>PostgreSQL</productname> also provides event triggers. Unlike regular 13 triggers, which are attached to a single table and capture only DML events, 14 event triggers are global to a particular database and are capable of 15 capturing DDL events. 16 </para> 17 18 <para> 19 Like regular triggers, event triggers can be written in any procedural 20 language that includes event trigger support, or in C, but not in plain 21 SQL. 22 </para> 23 24 <sect1 id="event-trigger-definition"> 25 <title>Overview of Event Trigger Behavior</title> 26 27 <para> 28 An event trigger fires whenever the event with which it is associated 29 occurs in the database in which it is defined. Currently, the only 30 supported events are 31 <literal>ddl_command_start</literal>, 32 <literal>ddl_command_end</literal>, 33 <literal>table_rewrite</literal> 34 and <literal>sql_drop</literal>. 35 Support for additional events may be added in future releases. 36 </para> 37 38 <para> 39 The <literal>ddl_command_start</literal> event occurs just before the 40 execution of a <literal>CREATE</literal>, <literal>ALTER</literal>, <literal>DROP</literal>, 41 <literal>SECURITY LABEL</literal>, 42 <literal>COMMENT</literal>, <literal>GRANT</literal> or <literal>REVOKE</literal> 43 command. No check whether the affected object exists or doesn't exist is 44 performed before the event trigger fires. 45 As an exception, however, this event does not occur for 46 DDL commands targeting shared objects — databases, roles, and tablespaces 47 — or for commands targeting event triggers themselves. The event trigger 48 mechanism does not support these object types. 49 <literal>ddl_command_start</literal> also occurs just before the execution of a 50 <literal>SELECT INTO</literal> command, since this is equivalent to 51 <literal>CREATE TABLE AS</literal>. 52 </para> 53 54 <para> 55 The <literal>ddl_command_end</literal> event occurs just after the execution of 56 this same set of commands. To obtain more details on the <acronym>DDL</acronym> 57 operations that took place, use the set-returning function 58 <literal>pg_event_trigger_ddl_commands()</literal> from the 59 <literal>ddl_command_end</literal> event trigger code (see 60 <xref linkend="functions-event-triggers"/>). Note that the trigger fires 61 after the actions have taken place (but before the transaction commits), 62 and thus the system catalogs can be read as already changed. 63 </para> 64 65 <para> 66 The <literal>sql_drop</literal> event occurs just before the 67 <literal>ddl_command_end</literal> event trigger for any operation that drops 68 database objects. To list the objects that have been dropped, use the 69 set-returning function <literal>pg_event_trigger_dropped_objects()</literal> from the 70 <literal>sql_drop</literal> event trigger code (see 71 <xref linkend="functions-event-triggers"/>). Note that 72 the trigger is executed after the objects have been deleted from the 73 system catalogs, so it's not possible to look them up anymore. 74 </para> 75 76 <para> 77 The <literal>table_rewrite</literal> event occurs just before a table is 78 rewritten by some actions of the commands <literal>ALTER TABLE</literal> and 79 <literal>ALTER TYPE</literal>. While other 80 control statements are available to rewrite a table, 81 like <literal>CLUSTER</literal> and <literal>VACUUM</literal>, 82 the <literal>table_rewrite</literal> event is not triggered by them. 83 </para> 84 85 <para> 86 Event triggers (like other functions) cannot be executed in an aborted 87 transaction. Thus, if a DDL command fails with an error, any associated 88 <literal>ddl_command_end</literal> triggers will not be executed. Conversely, 89 if a <literal>ddl_command_start</literal> trigger fails with an error, no 90 further event triggers will fire, and no attempt will be made to execute 91 the command itself. Similarly, if a <literal>ddl_command_end</literal> trigger 92 fails with an error, the effects of the DDL statement will be rolled 93 back, just as they would be in any other case where the containing 94 transaction aborts. 95 </para> 96 97 <para> 98 For a complete list of commands supported by the event trigger mechanism, 99 see <xref linkend="event-trigger-matrix"/>. 100 </para> 101 102 <para> 103 Event triggers are created using the command <xref linkend="sql-createeventtrigger"/>. 104 In order to create an event trigger, you must first create a function with 105 the special return type <literal>event_trigger</literal>. This function 106 need not (and may not) return a value; the return type serves merely as 107 a signal that the function is to be invoked as an event trigger. 108 </para> 109 110 <para> 111 If more than one event trigger is defined for a particular event, they will 112 fire in alphabetical order by trigger name. 113 </para> 114 115 <para> 116 A trigger definition can also specify a <literal>WHEN</literal> 117 condition so that, for example, a <literal>ddl_command_start</literal> 118 trigger can be fired only for particular commands which the user wishes 119 to intercept. A common use of such triggers is to restrict the range of 120 DDL operations which users may perform. 121 </para> 122 </sect1> 123 124 <sect1 id="event-trigger-matrix"> 125 <title>Event Trigger Firing Matrix</title> 126 127 <para> 128 <xref linkend="event-trigger-by-command-tag"/> lists all commands 129 for which event triggers are supported. 130 </para> 131 132 <table id="event-trigger-by-command-tag"> 133 <title>Event Trigger Support by Command Tag</title> 134 <tgroup cols="6"> 135 <colspec colname="col1" colwidth="2*"/> 136 <colspec colname="col2" colwidth="1*"/> 137 <colspec colname="col3" colwidth="1*"/> 138 <colspec colname="col4" colwidth="1*"/> 139 <colspec colname="col5" colwidth="1*"/> 140 <colspec colname="col6" colwidth="1*"/> 141 <thead> 142 <row> 143 <entry>Command Tag</entry> 144 <entry><literal>ddl_&zwsp;command_&zwsp;start</literal></entry> 145 <entry><literal>ddl_&zwsp;command_&zwsp;end</literal></entry> 146 <entry><literal>sql_&zwsp;drop</literal></entry> 147 <entry><literal>table_&zwsp;rewrite</literal></entry> 148 <entry>Notes</entry> 149 </row> 150 </thead> 151 <tbody> 152 <row> 153 <entry align="left"><literal>ALTER AGGREGATE</literal></entry> 154 <entry align="center"><literal>X</literal></entry> 155 <entry align="center"><literal>X</literal></entry> 156 <entry align="center"><literal>-</literal></entry> 157 <entry align="center"><literal>-</literal></entry> 158 <entry align="left"></entry> 159 </row> 160 <row> 161 <entry align="left"><literal>ALTER COLLATION</literal></entry> 162 <entry align="center"><literal>X</literal></entry> 163 <entry align="center"><literal>X</literal></entry> 164 <entry align="center"><literal>-</literal></entry> 165 <entry align="center"><literal>-</literal></entry> 166 <entry align="left"></entry> 167 </row> 168 <row> 169 <entry align="left"><literal>ALTER CONVERSION</literal></entry> 170 <entry align="center"><literal>X</literal></entry> 171 <entry align="center"><literal>X</literal></entry> 172 <entry align="center"><literal>-</literal></entry> 173 <entry align="center"><literal>-</literal></entry> 174 <entry align="left"></entry> 175 </row> 176 <row> 177 <entry align="left"><literal>ALTER DOMAIN</literal></entry> 178 <entry align="center"><literal>X</literal></entry> 179 <entry align="center"><literal>X</literal></entry> 180 <entry align="center"><literal>-</literal></entry> 181 <entry align="center"><literal>-</literal></entry> 182 <entry align="left"></entry> 183 </row> 184 <row> 185 <entry align="left"><literal>ALTER DEFAULT PRIVILEGES</literal></entry> 186 <entry align="center"><literal>X</literal></entry> 187 <entry align="center"><literal>X</literal></entry> 188 <entry align="center"><literal>-</literal></entry> 189 <entry align="center"><literal>-</literal></entry> 190 <entry align="left"></entry> 191 </row> 192 <row> 193 <entry align="left"><literal>ALTER EXTENSION</literal></entry> 194 <entry align="center"><literal>X</literal></entry> 195 <entry align="center"><literal>X</literal></entry> 196 <entry align="center"><literal>-</literal></entry> 197 <entry align="center"><literal>-</literal></entry> 198 <entry align="left"></entry> 199 </row> 200 <row> 201 <entry align="left"><literal>ALTER FOREIGN DATA WRAPPER</literal></entry> 202 <entry align="center"><literal>X</literal></entry> 203 <entry align="center"><literal>X</literal></entry> 204 <entry align="center"><literal>-</literal></entry> 205 <entry align="center"><literal>-</literal></entry> 206 <entry align="left"></entry> 207 </row> 208 <row> 209 <entry align="left"><literal>ALTER FOREIGN TABLE</literal></entry> 210 <entry align="center"><literal>X</literal></entry> 211 <entry align="center"><literal>X</literal></entry> 212 <entry align="center"><literal>X</literal></entry> 213 <entry align="center"><literal>-</literal></entry> 214 <entry align="left"></entry> 215 </row> 216 <row> 217 <entry align="left"><literal>ALTER FUNCTION</literal></entry> 218 <entry align="center"><literal>X</literal></entry> 219 <entry align="center"><literal>X</literal></entry> 220 <entry align="center"><literal>-</literal></entry> 221 <entry align="center"><literal>-</literal></entry> 222 <entry align="left"></entry> 223 </row> 224 <row> 225 <entry align="left"><literal>ALTER LANGUAGE</literal></entry> 226 <entry align="center"><literal>X</literal></entry> 227 <entry align="center"><literal>X</literal></entry> 228 <entry align="center"><literal>-</literal></entry> 229 <entry align="center"><literal>-</literal></entry> 230 <entry align="left"></entry> 231 </row> 232 <row> 233 <entry align="left"><literal>ALTER LARGE OBJECT</literal></entry> 234 <entry align="center"><literal>X</literal></entry> 235 <entry align="center"><literal>X</literal></entry> 236 <entry align="center"><literal>-</literal></entry> 237 <entry align="center"><literal>-</literal></entry> 238 <entry align="left"></entry> 239 </row> 240 <row> 241 <entry align="left"><literal>ALTER MATERIALIZED VIEW</literal></entry> 242 <entry align="center"><literal>X</literal></entry> 243 <entry align="center"><literal>X</literal></entry> 244 <entry align="center"><literal>-</literal></entry> 245 <entry align="center"><literal>-</literal></entry> 246 <entry align="left"></entry> 247 </row> 248 <row> 249 <entry align="left"><literal>ALTER OPERATOR</literal></entry> 250 <entry align="center"><literal>X</literal></entry> 251 <entry align="center"><literal>X</literal></entry> 252 <entry align="center"><literal>-</literal></entry> 253 <entry align="center"><literal>-</literal></entry> 254 <entry align="left"></entry> 255 </row> 256 <row> 257 <entry align="left"><literal>ALTER OPERATOR CLASS</literal></entry> 258 <entry align="center"><literal>X</literal></entry> 259 <entry align="center"><literal>X</literal></entry> 260 <entry align="center"><literal>-</literal></entry> 261 <entry align="center"><literal>-</literal></entry> 262 <entry align="left"></entry> 263 </row> 264 <row> 265 <entry align="left"><literal>ALTER OPERATOR FAMILY</literal></entry> 266 <entry align="center"><literal>X</literal></entry> 267 <entry align="center"><literal>X</literal></entry> 268 <entry align="center"><literal>-</literal></entry> 269 <entry align="center"><literal>-</literal></entry> 270 <entry align="left"></entry> 271 </row> 272 <row> 273 <entry align="left"><literal>ALTER POLICY</literal></entry> 274 <entry align="center"><literal>X</literal></entry> 275 <entry align="center"><literal>X</literal></entry> 276 <entry align="center"><literal>-</literal></entry> 277 <entry align="center"><literal>-</literal></entry> 278 <entry align="left"></entry> 279 </row> 280 <row> 281 <entry align="left"><literal>ALTER PROCEDURE</literal></entry> 282 <entry align="center"><literal>X</literal></entry> 283 <entry align="center"><literal>X</literal></entry> 284 <entry align="center"><literal>-</literal></entry> 285 <entry align="center"><literal>-</literal></entry> 286 <entry align="left"></entry> 287 </row> 288 <row> 289 <entry align="left"><literal>ALTER PUBLICATION</literal></entry> 290 <entry align="center"><literal>X</literal></entry> 291 <entry align="center"><literal>X</literal></entry> 292 <entry align="center"><literal>-</literal></entry> 293 <entry align="center"><literal>-</literal></entry> 294 <entry align="left"></entry> 295 </row> 296 <row> 297 <entry align="left"><literal>ALTER SCHEMA</literal></entry> 298 <entry align="center"><literal>X</literal></entry> 299 <entry align="center"><literal>X</literal></entry> 300 <entry align="center"><literal>-</literal></entry> 301 <entry align="center"><literal>-</literal></entry> 302 <entry align="left"></entry> 303 </row> 304 <row> 305 <entry align="left"><literal>ALTER SEQUENCE</literal></entry> 306 <entry align="center"><literal>X</literal></entry> 307 <entry align="center"><literal>X</literal></entry> 308 <entry align="center"><literal>-</literal></entry> 309 <entry align="center"><literal>-</literal></entry> 310 <entry align="left"></entry> 311 </row> 312 <row> 313 <entry align="left"><literal>ALTER SERVER</literal></entry> 314 <entry align="center"><literal>X</literal></entry> 315 <entry align="center"><literal>X</literal></entry> 316 <entry align="center"><literal>-</literal></entry> 317 <entry align="center"><literal>-</literal></entry> 318 <entry align="left"></entry> 319 </row> 320 <row> 321 <entry align="left"><literal>ALTER STATISTICS</literal></entry> 322 <entry align="center"><literal>X</literal></entry> 323 <entry align="center"><literal>X</literal></entry> 324 <entry align="center"><literal>-</literal></entry> 325 <entry align="center"><literal>-</literal></entry> 326 <entry align="left"></entry> 327 </row> 328 <row> 329 <entry align="left"><literal>ALTER SUBSCRIPTION</literal></entry> 330 <entry align="center"><literal>X</literal></entry> 331 <entry align="center"><literal>X</literal></entry> 332 <entry align="center"><literal>-</literal></entry> 333 <entry align="center"><literal>-</literal></entry> 334 <entry align="left"></entry> 335 </row> 336 <row> 337 <entry align="left"><literal>ALTER TABLE</literal></entry> 338 <entry align="center"><literal>X</literal></entry> 339 <entry align="center"><literal>X</literal></entry> 340 <entry align="center"><literal>X</literal></entry> 341 <entry align="center"><literal>X</literal></entry> 342 <entry align="left"></entry> 343 </row> 344 <row> 345 <entry align="left"><literal>ALTER TEXT SEARCH CONFIGURATION</literal></entry> 346 <entry align="center"><literal>X</literal></entry> 347 <entry align="center"><literal>X</literal></entry> 348 <entry align="center"><literal>-</literal></entry> 349 <entry align="center"><literal>-</literal></entry> 350 <entry align="left"></entry> 351 </row> 352 <row> 353 <entry align="left"><literal>ALTER TEXT SEARCH DICTIONARY</literal></entry> 354 <entry align="center"><literal>X</literal></entry> 355 <entry align="center"><literal>X</literal></entry> 356 <entry align="center"><literal>-</literal></entry> 357 <entry align="center"><literal>-</literal></entry> 358 <entry align="left"></entry> 359 </row> 360 <row> 361 <entry align="left"><literal>ALTER TEXT SEARCH PARSER</literal></entry> 362 <entry align="center"><literal>X</literal></entry> 363 <entry align="center"><literal>X</literal></entry> 364 <entry align="center"><literal>-</literal></entry> 365 <entry align="center"><literal>-</literal></entry> 366 <entry align="left"></entry> 367 </row> 368 <row> 369 <entry align="left"><literal>ALTER TEXT SEARCH TEMPLATE</literal></entry> 370 <entry align="center"><literal>X</literal></entry> 371 <entry align="center"><literal>X</literal></entry> 372 <entry align="center"><literal>-</literal></entry> 373 <entry align="center"><literal>-</literal></entry> 374 <entry align="left"></entry> 375 </row> 376 <row> 377 <entry align="left"><literal>ALTER TRIGGER</literal></entry> 378 <entry align="center"><literal>X</literal></entry> 379 <entry align="center"><literal>X</literal></entry> 380 <entry align="center"><literal>-</literal></entry> 381 <entry align="center"><literal>-</literal></entry> 382 <entry align="left"></entry> 383 </row> 384 <row> 385 <entry align="left"><literal>ALTER TYPE</literal></entry> 386 <entry align="center"><literal>X</literal></entry> 387 <entry align="center"><literal>X</literal></entry> 388 <entry align="center"><literal>-</literal></entry> 389 <entry align="center"><literal>X</literal></entry> 390 <entry align="left"></entry> 391 </row> 392 <row> 393 <entry align="left"><literal>ALTER USER MAPPING</literal></entry> 394 <entry align="center"><literal>X</literal></entry> 395 <entry align="center"><literal>X</literal></entry> 396 <entry align="center"><literal>-</literal></entry> 397 <entry align="center"><literal>-</literal></entry> 398 <entry align="left"></entry> 399 </row> 400 <row> 401 <entry align="left"><literal>ALTER VIEW</literal></entry> 402 <entry align="center"><literal>X</literal></entry> 403 <entry align="center"><literal>X</literal></entry> 404 <entry align="center"><literal>-</literal></entry> 405 <entry align="center"><literal>-</literal></entry> 406 <entry align="left"></entry> 407 </row> 408 <row> 409 <entry align="left"><literal>COMMENT</literal></entry> 410 <entry align="center"><literal>X</literal></entry> 411 <entry align="center"><literal>X</literal></entry> 412 <entry align="center"><literal>-</literal></entry> 413 <entry align="center"><literal>-</literal></entry> 414 <entry align="left">Only for local objects</entry> 415 </row> 416 <row> 417 <entry align="left"><literal>CREATE ACCESS METHOD</literal></entry> 418 <entry align="center"><literal>X</literal></entry> 419 <entry align="center"><literal>X</literal></entry> 420 <entry align="center"><literal>-</literal></entry> 421 <entry align="center"><literal>-</literal></entry> 422 <entry align="left"></entry> 423 </row> 424 <row> 425 <entry align="left"><literal>CREATE AGGREGATE</literal></entry> 426 <entry align="center"><literal>X</literal></entry> 427 <entry align="center"><literal>X</literal></entry> 428 <entry align="center"><literal>-</literal></entry> 429 <entry align="center"><literal>-</literal></entry> 430 <entry align="left"></entry> 431 </row> 432 <row> 433 <entry align="left"><literal>CREATE CAST</literal></entry> 434 <entry align="center"><literal>X</literal></entry> 435 <entry align="center"><literal>X</literal></entry> 436 <entry align="center"><literal>-</literal></entry> 437 <entry align="center"><literal>-</literal></entry> 438 <entry align="left"></entry> 439 </row> 440 <row> 441 <entry align="left"><literal>CREATE COLLATION</literal></entry> 442 <entry align="center"><literal>X</literal></entry> 443 <entry align="center"><literal>X</literal></entry> 444 <entry align="center"><literal>-</literal></entry> 445 <entry align="center"><literal>-</literal></entry> 446 <entry align="left"></entry> 447 </row> 448 <row> 449 <entry align="left"><literal>CREATE CONVERSION</literal></entry> 450 <entry align="center"><literal>X</literal></entry> 451 <entry align="center"><literal>X</literal></entry> 452 <entry align="center"><literal>-</literal></entry> 453 <entry align="center"><literal>-</literal></entry> 454 <entry align="left"></entry> 455 </row> 456 <row> 457 <entry align="left"><literal>CREATE DOMAIN</literal></entry> 458 <entry align="center"><literal>X</literal></entry> 459 <entry align="center"><literal>X</literal></entry> 460 <entry align="center"><literal>-</literal></entry> 461 <entry align="center"><literal>-</literal></entry> 462 <entry align="left"></entry> 463 </row> 464 <row> 465 <entry align="left"><literal>CREATE EXTENSION</literal></entry> 466 <entry align="center"><literal>X</literal></entry> 467 <entry align="center"><literal>X</literal></entry> 468 <entry align="center"><literal>-</literal></entry> 469 <entry align="center"><literal>-</literal></entry> 470 <entry align="left"></entry> 471 </row> 472 <row> 473 <entry align="left"><literal>CREATE FOREIGN DATA WRAPPER</literal></entry> 474 <entry align="center"><literal>X</literal></entry> 475 <entry align="center"><literal>X</literal></entry> 476 <entry align="center"><literal>-</literal></entry> 477 <entry align="center"><literal>-</literal></entry> 478 <entry align="left"></entry> 479 </row> 480 <row> 481 <entry align="left"><literal>CREATE FOREIGN TABLE</literal></entry> 482 <entry align="center"><literal>X</literal></entry> 483 <entry align="center"><literal>X</literal></entry> 484 <entry align="center"><literal>-</literal></entry> 485 <entry align="center"><literal>-</literal></entry> 486 <entry align="left"></entry> 487 </row> 488 <row> 489 <entry align="left"><literal>CREATE FUNCTION</literal></entry> 490 <entry align="center"><literal>X</literal></entry> 491 <entry align="center"><literal>X</literal></entry> 492 <entry align="center"><literal>-</literal></entry> 493 <entry align="center"><literal>-</literal></entry> 494 <entry align="left"></entry> 495 </row> 496 <row> 497 <entry align="left"><literal>CREATE INDEX</literal></entry> 498 <entry align="center"><literal>X</literal></entry> 499 <entry align="center"><literal>X</literal></entry> 500 <entry align="center"><literal>-</literal></entry> 501 <entry align="center"><literal>-</literal></entry> 502 <entry align="left"></entry> 503 </row> 504 <row> 505 <entry align="left"><literal>CREATE LANGUAGE</literal></entry> 506 <entry align="center"><literal>X</literal></entry> 507 <entry align="center"><literal>X</literal></entry> 508 <entry align="center"><literal>-</literal></entry> 509 <entry align="center"><literal>-</literal></entry> 510 <entry align="left"></entry> 511 </row> 512 <row> 513 <entry align="left"><literal>CREATE MATERIALIZED VIEW</literal></entry> 514 <entry align="center"><literal>X</literal></entry> 515 <entry align="center"><literal>X</literal></entry> 516 <entry align="center"><literal>-</literal></entry> 517 <entry align="center"><literal>-</literal></entry> 518 <entry align="left"></entry> 519 </row> 520 <row> 521 <entry align="left"><literal>CREATE OPERATOR</literal></entry> 522 <entry align="center"><literal>X</literal></entry> 523 <entry align="center"><literal>X</literal></entry> 524 <entry align="center"><literal>-</literal></entry> 525 <entry align="center"><literal>-</literal></entry> 526 <entry align="left"></entry> 527 </row> 528 <row> 529 <entry align="left"><literal>CREATE OPERATOR CLASS</literal></entry> 530 <entry align="center"><literal>X</literal></entry> 531 <entry align="center"><literal>X</literal></entry> 532 <entry align="center"><literal>-</literal></entry> 533 <entry align="center"><literal>-</literal></entry> 534 <entry align="left"></entry> 535 </row> 536 <row> 537 <entry align="left"><literal>CREATE OPERATOR FAMILY</literal></entry> 538 <entry align="center"><literal>X</literal></entry> 539 <entry align="center"><literal>X</literal></entry> 540 <entry align="center"><literal>-</literal></entry> 541 <entry align="center"><literal>-</literal></entry> 542 <entry align="left"></entry> 543 </row> 544 <row> 545 <entry align="left"><literal>CREATE POLICY</literal></entry> 546 <entry align="center"><literal>X</literal></entry> 547 <entry align="center"><literal>X</literal></entry> 548 <entry align="center"><literal>-</literal></entry> 549 <entry align="center"><literal>-</literal></entry> 550 <entry align="left"></entry> 551 </row> 552 <row> 553 <entry align="left"><literal>CREATE PROCEDURE</literal></entry> 554 <entry align="center"><literal>X</literal></entry> 555 <entry align="center"><literal>X</literal></entry> 556 <entry align="center"><literal>-</literal></entry> 557 <entry align="center"><literal>-</literal></entry> 558 <entry align="left"></entry> 559 </row> 560 <row> 561 <entry align="left"><literal>CREATE PUBLICATION</literal></entry> 562 <entry align="center"><literal>X</literal></entry> 563 <entry align="center"><literal>X</literal></entry> 564 <entry align="center"><literal>-</literal></entry> 565 <entry align="center"><literal>-</literal></entry> 566 <entry align="left"></entry> 567 </row> 568 <row> 569 <entry align="left"><literal>CREATE RULE</literal></entry> 570 <entry align="center"><literal>X</literal></entry> 571 <entry align="center"><literal>X</literal></entry> 572 <entry align="center"><literal>-</literal></entry> 573 <entry align="center"><literal>-</literal></entry> 574 <entry align="left"></entry> 575 </row> 576 <row> 577 <entry align="left"><literal>CREATE SCHEMA</literal></entry> 578 <entry align="center"><literal>X</literal></entry> 579 <entry align="center"><literal>X</literal></entry> 580 <entry align="center"><literal>-</literal></entry> 581 <entry align="center"><literal>-</literal></entry> 582 <entry align="left"></entry> 583 </row> 584 <row> 585 <entry align="left"><literal>CREATE SEQUENCE</literal></entry> 586 <entry align="center"><literal>X</literal></entry> 587 <entry align="center"><literal>X</literal></entry> 588 <entry align="center"><literal>-</literal></entry> 589 <entry align="center"><literal>-</literal></entry> 590 <entry align="left"></entry> 591 </row> 592 <row> 593 <entry align="left"><literal>CREATE SERVER</literal></entry> 594 <entry align="center"><literal>X</literal></entry> 595 <entry align="center"><literal>X</literal></entry> 596 <entry align="center"><literal>-</literal></entry> 597 <entry align="center"><literal>-</literal></entry> 598 <entry align="left"></entry> 599 </row> 600 <row> 601 <entry align="left"><literal>CREATE STATISTICS</literal></entry> 602 <entry align="center"><literal>X</literal></entry> 603 <entry align="center"><literal>X</literal></entry> 604 <entry align="center"><literal>-</literal></entry> 605 <entry align="center"><literal>-</literal></entry> 606 <entry align="left"></entry> 607 </row> 608 <row> 609 <entry align="left"><literal>CREATE SUBSCRIPTION</literal></entry> 610 <entry align="center"><literal>X</literal></entry> 611 <entry align="center"><literal>X</literal></entry> 612 <entry align="center"><literal>-</literal></entry> 613 <entry align="center"><literal>-</literal></entry> 614 <entry align="left"></entry> 615 </row> 616 <row> 617 <entry align="left"><literal>CREATE TABLE</literal></entry> 618 <entry align="center"><literal>X</literal></entry> 619 <entry align="center"><literal>X</literal></entry> 620 <entry align="center"><literal>-</literal></entry> 621 <entry align="center"><literal>-</literal></entry> 622 <entry align="left"></entry> 623 </row> 624 <row> 625 <entry align="left"><literal>CREATE TABLE AS</literal></entry> 626 <entry align="center"><literal>X</literal></entry> 627 <entry align="center"><literal>X</literal></entry> 628 <entry align="center"><literal>-</literal></entry> 629 <entry align="center"><literal>-</literal></entry> 630 <entry align="left"></entry> 631 </row> 632 <row> 633 <entry align="left"><literal>CREATE TEXT SEARCH CONFIGURATION</literal></entry> 634 <entry align="center"><literal>X</literal></entry> 635 <entry align="center"><literal>X</literal></entry> 636 <entry align="center"><literal>-</literal></entry> 637 <entry align="center"><literal>-</literal></entry> 638 <entry align="left"></entry> 639 </row> 640 <row> 641 <entry align="left"><literal>CREATE TEXT SEARCH DICTIONARY</literal></entry> 642 <entry align="center"><literal>X</literal></entry> 643 <entry align="center"><literal>X</literal></entry> 644 <entry align="center"><literal>-</literal></entry> 645 <entry align="center"><literal>-</literal></entry> 646 <entry align="left"></entry> 647 </row> 648 <row> 649 <entry align="left"><literal>CREATE TEXT SEARCH PARSER</literal></entry> 650 <entry align="center"><literal>X</literal></entry> 651 <entry align="center"><literal>X</literal></entry> 652 <entry align="center"><literal>-</literal></entry> 653 <entry align="center"><literal>-</literal></entry> 654 <entry align="left"></entry> 655 </row> 656 <row> 657 <entry align="left"><literal>CREATE TEXT SEARCH TEMPLATE</literal></entry> 658 <entry align="center"><literal>X</literal></entry> 659 <entry align="center"><literal>X</literal></entry> 660 <entry align="center"><literal>-</literal></entry> 661 <entry align="center"><literal>-</literal></entry> 662 <entry align="left"></entry> 663 </row> 664 <row> 665 <entry align="left"><literal>CREATE TRIGGER</literal></entry> 666 <entry align="center"><literal>X</literal></entry> 667 <entry align="center"><literal>X</literal></entry> 668 <entry align="center"><literal>-</literal></entry> 669 <entry align="center"><literal>-</literal></entry> 670 <entry align="left"></entry> 671 </row> 672 <row> 673 <entry align="left"><literal>CREATE TYPE</literal></entry> 674 <entry align="center"><literal>X</literal></entry> 675 <entry align="center"><literal>X</literal></entry> 676 <entry align="center"><literal>-</literal></entry> 677 <entry align="center"><literal>-</literal></entry> 678 <entry align="left"></entry> 679 </row> 680 <row> 681 <entry align="left"><literal>CREATE USER MAPPING</literal></entry> 682 <entry align="center"><literal>X</literal></entry> 683 <entry align="center"><literal>X</literal></entry> 684 <entry align="center"><literal>-</literal></entry> 685 <entry align="center"><literal>-</literal></entry> 686 <entry align="left"></entry> 687 </row> 688 <row> 689 <entry align="left"><literal>CREATE VIEW</literal></entry> 690 <entry align="center"><literal>X</literal></entry> 691 <entry align="center"><literal>X</literal></entry> 692 <entry align="center"><literal>-</literal></entry> 693 <entry align="center"><literal>-</literal></entry> 694 <entry align="left"></entry> 695 </row> 696 <row> 697 <entry align="left"><literal>DROP ACCESS METHOD</literal></entry> 698 <entry align="center"><literal>X</literal></entry> 699 <entry align="center"><literal>X</literal></entry> 700 <entry align="center"><literal>X</literal></entry> 701 <entry align="center"><literal>-</literal></entry> 702 <entry align="left"></entry> 703 </row> 704 <row> 705 <entry align="left"><literal>DROP AGGREGATE</literal></entry> 706 <entry align="center"><literal>X</literal></entry> 707 <entry align="center"><literal>X</literal></entry> 708 <entry align="center"><literal>X</literal></entry> 709 <entry align="center"><literal>-</literal></entry> 710 <entry align="left"></entry> 711 </row> 712 <row> 713 <entry align="left"><literal>DROP CAST</literal></entry> 714 <entry align="center"><literal>X</literal></entry> 715 <entry align="center"><literal>X</literal></entry> 716 <entry align="center"><literal>X</literal></entry> 717 <entry align="center"><literal>-</literal></entry> 718 <entry align="left"></entry> 719 </row> 720 <row> 721 <entry align="left"><literal>DROP COLLATION</literal></entry> 722 <entry align="center"><literal>X</literal></entry> 723 <entry align="center"><literal>X</literal></entry> 724 <entry align="center"><literal>X</literal></entry> 725 <entry align="center"><literal>-</literal></entry> 726 <entry align="left"></entry> 727 </row> 728 <row> 729 <entry align="left"><literal>DROP CONVERSION</literal></entry> 730 <entry align="center"><literal>X</literal></entry> 731 <entry align="center"><literal>X</literal></entry> 732 <entry align="center"><literal>X</literal></entry> 733 <entry align="center"><literal>-</literal></entry> 734 <entry align="left"></entry> 735 </row> 736 <row> 737 <entry align="left"><literal>DROP DOMAIN</literal></entry> 738 <entry align="center"><literal>X</literal></entry> 739 <entry align="center"><literal>X</literal></entry> 740 <entry align="center"><literal>X</literal></entry> 741 <entry align="center"><literal>-</literal></entry> 742 <entry align="left"></entry> 743 </row> 744 <row> 745 <entry align="left"><literal>DROP EXTENSION</literal></entry> 746 <entry align="center"><literal>X</literal></entry> 747 <entry align="center"><literal>X</literal></entry> 748 <entry align="center"><literal>X</literal></entry> 749 <entry align="center"><literal>-</literal></entry> 750 <entry align="left"></entry> 751 </row> 752 <row> 753 <entry align="left"><literal>DROP FOREIGN DATA WRAPPER</literal></entry> 754 <entry align="center"><literal>X</literal></entry> 755 <entry align="center"><literal>X</literal></entry> 756 <entry align="center"><literal>X</literal></entry> 757 <entry align="center"><literal>-</literal></entry> 758 <entry align="left"></entry> 759 </row> 760 <row> 761 <entry align="left"><literal>DROP FOREIGN TABLE</literal></entry> 762 <entry align="center"><literal>X</literal></entry> 763 <entry align="center"><literal>X</literal></entry> 764 <entry align="center"><literal>X</literal></entry> 765 <entry align="center"><literal>-</literal></entry> 766 <entry align="left"></entry> 767 </row> 768 <row> 769 <entry align="left"><literal>DROP FUNCTION</literal></entry> 770 <entry align="center"><literal>X</literal></entry> 771 <entry align="center"><literal>X</literal></entry> 772 <entry align="center"><literal>X</literal></entry> 773 <entry align="center"><literal>-</literal></entry> 774 <entry align="left"></entry> 775 </row> 776 <row> 777 <entry align="left"><literal>DROP INDEX</literal></entry> 778 <entry align="center"><literal>X</literal></entry> 779 <entry align="center"><literal>X</literal></entry> 780 <entry align="center"><literal>X</literal></entry> 781 <entry align="center"><literal>-</literal></entry> 782 <entry align="left"></entry> 783 </row> 784 <row> 785 <entry align="left"><literal>DROP LANGUAGE</literal></entry> 786 <entry align="center"><literal>X</literal></entry> 787 <entry align="center"><literal>X</literal></entry> 788 <entry align="center"><literal>X</literal></entry> 789 <entry align="center"><literal>-</literal></entry> 790 <entry align="left"></entry> 791 </row> 792 <row> 793 <entry align="left"><literal>DROP MATERIALIZED VIEW</literal></entry> 794 <entry align="center"><literal>X</literal></entry> 795 <entry align="center"><literal>X</literal></entry> 796 <entry align="center"><literal>X</literal></entry> 797 <entry align="center"><literal>-</literal></entry> 798 <entry align="left"></entry> 799 </row> 800 <row> 801 <entry align="left"><literal>DROP OPERATOR</literal></entry> 802 <entry align="center"><literal>X</literal></entry> 803 <entry align="center"><literal>X</literal></entry> 804 <entry align="center"><literal>X</literal></entry> 805 <entry align="center"><literal>-</literal></entry> 806 <entry align="left"></entry> 807 </row> 808 <row> 809 <entry align="left"><literal>DROP OPERATOR CLASS</literal></entry> 810 <entry align="center"><literal>X</literal></entry> 811 <entry align="center"><literal>X</literal></entry> 812 <entry align="center"><literal>X</literal></entry> 813 <entry align="center"><literal>-</literal></entry> 814 <entry align="left"></entry> 815 </row> 816 <row> 817 <entry align="left"><literal>DROP OPERATOR FAMILY</literal></entry> 818 <entry align="center"><literal>X</literal></entry> 819 <entry align="center"><literal>X</literal></entry> 820 <entry align="center"><literal>X</literal></entry> 821 <entry align="center"><literal>-</literal></entry> 822 <entry align="left"></entry> 823 </row> 824 <row> 825 <entry align="left"><literal>DROP OWNED</literal></entry> 826 <entry align="center"><literal>X</literal></entry> 827 <entry align="center"><literal>X</literal></entry> 828 <entry align="center"><literal>X</literal></entry> 829 <entry align="center"><literal>-</literal></entry> 830 <entry align="left"></entry> 831 </row> 832 <row> 833 <entry align="left"><literal>DROP POLICY</literal></entry> 834 <entry align="center"><literal>X</literal></entry> 835 <entry align="center"><literal>X</literal></entry> 836 <entry align="center"><literal>X</literal></entry> 837 <entry align="center"><literal>-</literal></entry> 838 <entry align="left"></entry> 839 </row> 840 <row> 841 <entry align="left"><literal>DROP PROCEDURE</literal></entry> 842 <entry align="center"><literal>X</literal></entry> 843 <entry align="center"><literal>X</literal></entry> 844 <entry align="center"><literal>X</literal></entry> 845 <entry align="center"><literal>-</literal></entry> 846 <entry align="left"></entry> 847 </row> 848 <row> 849 <entry align="left"><literal>DROP PUBLICATION</literal></entry> 850 <entry align="center"><literal>X</literal></entry> 851 <entry align="center"><literal>X</literal></entry> 852 <entry align="center"><literal>X</literal></entry> 853 <entry align="center"><literal>-</literal></entry> 854 <entry align="left"></entry> 855 </row> 856 <row> 857 <entry align="left"><literal>DROP RULE</literal></entry> 858 <entry align="center"><literal>X</literal></entry> 859 <entry align="center"><literal>X</literal></entry> 860 <entry align="center"><literal>X</literal></entry> 861 <entry align="center"><literal>-</literal></entry> 862 <entry align="left"></entry> 863 </row> 864 <row> 865 <entry align="left"><literal>DROP SCHEMA</literal></entry> 866 <entry align="center"><literal>X</literal></entry> 867 <entry align="center"><literal>X</literal></entry> 868 <entry align="center"><literal>X</literal></entry> 869 <entry align="center"><literal>-</literal></entry> 870 <entry align="left"></entry> 871 </row> 872 <row> 873 <entry align="left"><literal>DROP SEQUENCE</literal></entry> 874 <entry align="center"><literal>X</literal></entry> 875 <entry align="center"><literal>X</literal></entry> 876 <entry align="center"><literal>X</literal></entry> 877 <entry align="center"><literal>-</literal></entry> 878 <entry align="left"></entry> 879 </row> 880 <row> 881 <entry align="left"><literal>DROP SERVER</literal></entry> 882 <entry align="center"><literal>X</literal></entry> 883 <entry align="center"><literal>X</literal></entry> 884 <entry align="center"><literal>X</literal></entry> 885 <entry align="center"><literal>-</literal></entry> 886 <entry align="left"></entry> 887 </row> 888 <row> 889 <entry align="left"><literal>DROP STATISTICS</literal></entry> 890 <entry align="center"><literal>X</literal></entry> 891 <entry align="center"><literal>X</literal></entry> 892 <entry align="center"><literal>X</literal></entry> 893 <entry align="center"><literal>-</literal></entry> 894 <entry align="left"></entry> 895 </row> 896 <row> 897 <entry align="left"><literal>DROP SUBSCRIPTION</literal></entry> 898 <entry align="center"><literal>X</literal></entry> 899 <entry align="center"><literal>X</literal></entry> 900 <entry align="center"><literal>X</literal></entry> 901 <entry align="center"><literal>-</literal></entry> 902 <entry align="left"></entry> 903 </row> 904 <row> 905 <entry align="left"><literal>DROP TABLE</literal></entry> 906 <entry align="center"><literal>X</literal></entry> 907 <entry align="center"><literal>X</literal></entry> 908 <entry align="center"><literal>X</literal></entry> 909 <entry align="center"><literal>-</literal></entry> 910 <entry align="left"></entry> 911 </row> 912 <row> 913 <entry align="left"><literal>DROP TEXT SEARCH CONFIGURATION</literal></entry> 914 <entry align="center"><literal>X</literal></entry> 915 <entry align="center"><literal>X</literal></entry> 916 <entry align="center"><literal>X</literal></entry> 917 <entry align="center"><literal>-</literal></entry> 918 <entry align="left"></entry> 919 </row> 920 <row> 921 <entry align="left"><literal>DROP TEXT SEARCH DICTIONARY</literal></entry> 922 <entry align="center"><literal>X</literal></entry> 923 <entry align="center"><literal>X</literal></entry> 924 <entry align="center"><literal>X</literal></entry> 925 <entry align="center"><literal>-</literal></entry> 926 <entry align="left"></entry> 927 </row> 928 <row> 929 <entry align="left"><literal>DROP TEXT SEARCH PARSER</literal></entry> 930 <entry align="center"><literal>X</literal></entry> 931 <entry align="center"><literal>X</literal></entry> 932 <entry align="center"><literal>X</literal></entry> 933 <entry align="center"><literal>-</literal></entry> 934 <entry align="left"></entry> 935 </row> 936 <row> 937 <entry align="left"><literal>DROP TEXT SEARCH TEMPLATE</literal></entry> 938 <entry align="center"><literal>X</literal></entry> 939 <entry align="center"><literal>X</literal></entry> 940 <entry align="center"><literal>X</literal></entry> 941 <entry align="center"><literal>-</literal></entry> 942 <entry align="left"></entry> 943 </row> 944 <row> 945 <entry align="left"><literal>DROP TRIGGER</literal></entry> 946 <entry align="center"><literal>X</literal></entry> 947 <entry align="center"><literal>X</literal></entry> 948 <entry align="center"><literal>X</literal></entry> 949 <entry align="center"><literal>-</literal></entry> 950 <entry align="left"></entry> 951 </row> 952 <row> 953 <entry align="left"><literal>DROP TYPE</literal></entry> 954 <entry align="center"><literal>X</literal></entry> 955 <entry align="center"><literal>X</literal></entry> 956 <entry align="center"><literal>X</literal></entry> 957 <entry align="center"><literal>-</literal></entry> 958 <entry align="left"></entry> 959 </row> 960 <row> 961 <entry align="left"><literal>DROP USER MAPPING</literal></entry> 962 <entry align="center"><literal>X</literal></entry> 963 <entry align="center"><literal>X</literal></entry> 964 <entry align="center"><literal>X</literal></entry> 965 <entry align="center"><literal>-</literal></entry> 966 <entry align="left"></entry> 967 </row> 968 <row> 969 <entry align="left"><literal>DROP VIEW</literal></entry> 970 <entry align="center"><literal>X</literal></entry> 971 <entry align="center"><literal>X</literal></entry> 972 <entry align="center"><literal>X</literal></entry> 973 <entry align="center"><literal>-</literal></entry> 974 <entry align="left"></entry> 975 </row> 976 <row> 977 <entry align="left"><literal>GRANT</literal></entry> 978 <entry align="center"><literal>X</literal></entry> 979 <entry align="center"><literal>X</literal></entry> 980 <entry align="center"><literal>-</literal></entry> 981 <entry align="center"><literal>-</literal></entry> 982 <entry align="left">Only for local objects</entry> 983 </row> 984 <row> 985 <entry align="left"><literal>IMPORT FOREIGN SCHEMA</literal></entry> 986 <entry align="center"><literal>X</literal></entry> 987 <entry align="center"><literal>X</literal></entry> 988 <entry align="center"><literal>-</literal></entry> 989 <entry align="center"><literal>-</literal></entry> 990 <entry align="left"></entry> 991 </row> 992 <row> 993 <entry align="left"><literal>REFRESH MATERIALIZED VIEW</literal></entry> 994 <entry align="center"><literal>X</literal></entry> 995 <entry align="center"><literal>X</literal></entry> 996 <entry align="center"><literal>-</literal></entry> 997 <entry align="center"><literal>-</literal></entry> 998 <entry align="left"></entry> 999 </row> 1000 <row> 1001 <entry align="left"><literal>REVOKE</literal></entry> 1002 <entry align="center"><literal>X</literal></entry> 1003 <entry align="center"><literal>X</literal></entry> 1004 <entry align="center"><literal>-</literal></entry> 1005 <entry align="center"><literal>-</literal></entry> 1006 <entry align="left">Only for local objects</entry> 1007 </row> 1008 <row> 1009 <entry align="left"><literal>SECURITY LABEL</literal></entry> 1010 <entry align="center"><literal>X</literal></entry> 1011 <entry align="center"><literal>X</literal></entry> 1012 <entry align="center"><literal>-</literal></entry> 1013 <entry align="center"><literal>-</literal></entry> 1014 <entry align="left">Only for local objects</entry> 1015 </row> 1016 <row> 1017 <entry align="left"><literal>SELECT INTO</literal></entry> 1018 <entry align="center"><literal>X</literal></entry> 1019 <entry align="center"><literal>X</literal></entry> 1020 <entry align="center"><literal>-</literal></entry> 1021 <entry align="center"><literal>-</literal></entry> 1022 <entry align="left"></entry> 1023 </row> 1024 </tbody> 1025 </tgroup> 1026 </table> 1027 </sect1> 1028 1029 <sect1 id="event-trigger-interface"> 1030 <title>Writing Event Trigger Functions in C</title> 1031 1032 <indexterm zone="event-trigger-interface"> 1033 <primary>event trigger</primary> 1034 <secondary>in C</secondary> 1035 </indexterm> 1036 1037 <para> 1038 This section describes the low-level details of the interface to an 1039 event trigger function. This information is only needed when writing 1040 event trigger functions in C. If you are using a higher-level language 1041 then these details are handled for you. In most cases you should 1042 consider using a procedural language before writing your event triggers 1043 in C. The documentation of each procedural language explains how to 1044 write an event trigger in that language. 1045 </para> 1046 1047 <para> 1048 Event trigger functions must use the <quote>version 1</quote> function 1049 manager interface. 1050 </para> 1051 1052 <para> 1053 When a function is called by the event trigger manager, it is not passed 1054 any normal arguments, but it is passed a <quote>context</quote> pointer 1055 pointing to a <structname>EventTriggerData</structname> structure. C functions can 1056 check whether they were called from the event trigger manager or not by 1057 executing the macro: 1058<programlisting> 1059CALLED_AS_EVENT_TRIGGER(fcinfo) 1060</programlisting> 1061 which expands to: 1062<programlisting> 1063((fcinfo)->context != NULL && IsA((fcinfo)->context, EventTriggerData)) 1064</programlisting> 1065 If this returns true, then it is safe to cast 1066 <literal>fcinfo->context</literal> to type <literal>EventTriggerData 1067 *</literal> and make use of the pointed-to 1068 <structname>EventTriggerData</structname> structure. The function must 1069 <emphasis>not</emphasis> alter the <structname>EventTriggerData</structname> 1070 structure or any of the data it points to. 1071 </para> 1072 1073 <para> 1074 <structname>struct EventTriggerData</structname> is defined in 1075 <filename>commands/event_trigger.h</filename>: 1076 1077<programlisting> 1078typedef struct EventTriggerData 1079{ 1080 NodeTag type; 1081 const char *event; /* event name */ 1082 Node *parsetree; /* parse tree */ 1083 CommandTag tag; /* command tag */ 1084} EventTriggerData; 1085</programlisting> 1086 1087 where the members are defined as follows: 1088 1089 <variablelist> 1090 <varlistentry> 1091 <term><structfield>type</structfield></term> 1092 <listitem> 1093 <para> 1094 Always <literal>T_EventTriggerData</literal>. 1095 </para> 1096 </listitem> 1097 </varlistentry> 1098 1099 <varlistentry> 1100 <term><structfield>event</structfield></term> 1101 <listitem> 1102 <para> 1103 Describes the event for which the function is called, one of 1104 <literal>"ddl_command_start"</literal>, <literal>"ddl_command_end"</literal>, 1105 <literal>"sql_drop"</literal>, <literal>"table_rewrite"</literal>. 1106 See <xref linkend="event-trigger-definition"/> for the meaning of these 1107 events. 1108 </para> 1109 </listitem> 1110 </varlistentry> 1111 1112 <varlistentry> 1113 <term><structfield>parsetree</structfield></term> 1114 <listitem> 1115 <para> 1116 A pointer to the parse tree of the command. Check the PostgreSQL 1117 source code for details. The parse tree structure is subject to change 1118 without notice. 1119 </para> 1120 </listitem> 1121 </varlistentry> 1122 1123 <varlistentry> 1124 <term><structfield>tag</structfield></term> 1125 <listitem> 1126 <para> 1127 The command tag associated with the event for which the event trigger 1128 is run, for example <literal>"CREATE FUNCTION"</literal>. 1129 </para> 1130 </listitem> 1131 </varlistentry> 1132 </variablelist> 1133 </para> 1134 1135 <para> 1136 An event trigger function must return a <symbol>NULL</symbol> pointer 1137 (<emphasis>not</emphasis> an SQL null value, that is, do not 1138 set <parameter>isNull</parameter> true). 1139 </para> 1140 </sect1> 1141 1142 <sect1 id="event-trigger-example"> 1143 <title>A Complete Event Trigger Example</title> 1144 1145 <para> 1146 Here is a very simple example of an event trigger function written in C. 1147 (Examples of triggers written in procedural languages can be found in 1148 the documentation of the procedural languages.) 1149 </para> 1150 1151 <para> 1152 The function <function>noddl</function> raises an exception each time it is called. 1153 The event trigger definition associated the function with 1154 the <literal>ddl_command_start</literal> event. The effect is that all DDL 1155 commands (with the exceptions mentioned 1156 in <xref linkend="event-trigger-definition"/>) are prevented from running. 1157 </para> 1158 1159 <para> 1160 This is the source code of the trigger function: 1161<programlisting><![CDATA[ 1162#include "postgres.h" 1163#include "commands/event_trigger.h" 1164 1165 1166PG_MODULE_MAGIC; 1167 1168PG_FUNCTION_INFO_V1(noddl); 1169 1170Datum 1171noddl(PG_FUNCTION_ARGS) 1172{ 1173 EventTriggerData *trigdata; 1174 1175 if (!CALLED_AS_EVENT_TRIGGER(fcinfo)) /* internal error */ 1176 elog(ERROR, "not fired by event trigger manager"); 1177 1178 trigdata = (EventTriggerData *) fcinfo->context; 1179 1180 ereport(ERROR, 1181 (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE), 1182 errmsg("command \"%s\" denied", trigdata->tag))); 1183 1184 PG_RETURN_NULL(); 1185} 1186]]></programlisting> 1187 </para> 1188 1189 <para> 1190 After you have compiled the source code (see <xref linkend="dfunc"/>), 1191 declare the function and the triggers: 1192<programlisting> 1193CREATE FUNCTION noddl() RETURNS event_trigger 1194 AS 'noddl' LANGUAGE C; 1195 1196CREATE EVENT TRIGGER noddl ON ddl_command_start 1197 EXECUTE FUNCTION noddl(); 1198</programlisting> 1199 </para> 1200 1201 <para> 1202 Now you can test the operation of the trigger: 1203<screen> 1204=# \dy 1205 List of event triggers 1206 Name | Event | Owner | Enabled | Function | Tags 1207-------+-------------------+-------+---------+----------+------ 1208 noddl | ddl_command_start | dim | enabled | noddl | 1209(1 row) 1210 1211=# CREATE TABLE foo(id serial); 1212ERROR: command "CREATE TABLE" denied 1213</screen> 1214 </para> 1215 1216 <para> 1217 In this situation, in order to be able to run some DDL commands when you 1218 need to do so, you have to either drop the event trigger or disable it. It 1219 can be convenient to disable the trigger for only the duration of a 1220 transaction: 1221<programlisting> 1222BEGIN; 1223ALTER EVENT TRIGGER noddl DISABLE; 1224CREATE TABLE foo (id serial); 1225ALTER EVENT TRIGGER noddl ENABLE; 1226COMMIT; 1227</programlisting> 1228 (Recall that DDL commands on event triggers themselves are not affected by 1229 event triggers.) 1230 </para> 1231 </sect1> 1232 1233 <sect1 id="event-trigger-table-rewrite-example"> 1234 <title>A Table Rewrite Event Trigger Example</title> 1235 1236 <para> 1237 Thanks to the <literal>table_rewrite</literal> event, it is possible to implement 1238 a table rewriting policy only allowing the rewrite in maintenance windows. 1239 </para> 1240 1241 <para> 1242 Here's an example implementing such a policy. 1243<programlisting> 1244CREATE OR REPLACE FUNCTION no_rewrite() 1245 RETURNS event_trigger 1246 LANGUAGE plpgsql AS 1247$$ 1248--- 1249--- Implement local Table Rewriting policy: 1250--- public.foo is not allowed rewriting, ever 1251--- other tables are only allowed rewriting between 1am and 6am 1252--- unless they have more than 100 blocks 1253--- 1254DECLARE 1255 table_oid oid := pg_event_trigger_table_rewrite_oid(); 1256 current_hour integer := extract('hour' from current_time); 1257 pages integer; 1258 max_pages integer := 100; 1259BEGIN 1260 IF pg_event_trigger_table_rewrite_oid() = 'public.foo'::regclass 1261 THEN 1262 RAISE EXCEPTION 'you''re not allowed to rewrite the table %', 1263 table_oid::regclass; 1264 END IF; 1265 1266 SELECT INTO pages relpages FROM pg_class WHERE oid = table_oid; 1267 IF pages > max_pages 1268 THEN 1269 RAISE EXCEPTION 'rewrites only allowed for table with less than % pages', 1270 max_pages; 1271 END IF; 1272 1273 IF current_hour NOT BETWEEN 1 AND 6 1274 THEN 1275 RAISE EXCEPTION 'rewrites only allowed between 1am and 6am'; 1276 END IF; 1277END; 1278$$; 1279 1280CREATE EVENT TRIGGER no_rewrite_allowed 1281 ON table_rewrite 1282 EXECUTE FUNCTION no_rewrite(); 1283</programlisting> 1284 </para> 1285 </sect1> 1286</chapter> 1287