Line data Source code
1 : /*
2 : * task.c
3 : * framework for parallelizing pg_upgrade's once-in-each-database tasks
4 : *
5 : * This framework provides an efficient way of running the various
6 : * once-in-each-database tasks required by pg_upgrade. Specifically, it
7 : * parallelizes these tasks by managing a set of slots that follow a simple
8 : * state machine and by using libpq's asynchronous APIs to establish the
9 : * connections and run the queries. Callers simply need to create a callback
10 : * function and build/execute an UpgradeTask. A simple example follows:
11 : *
12 : * static void
13 : * my_process_cb(DbInfo *dbinfo, PGresult *res, void *arg)
14 : * {
15 : * for (int i = 0; i < PQntuples(res); i++)
16 : * {
17 : * ... process results ...
18 : * }
19 : * }
20 : *
21 : * void
22 : * my_task(ClusterInfo *cluster)
23 : * {
24 : * UpgradeTask *task = upgrade_task_create();
25 : *
26 : * upgrade_task_add_step(task,
27 : * "... query text ...",
28 : * my_process_cb,
29 : * true, // let the task free the PGresult
30 : * NULL); // "arg" pointer for callback
31 : * upgrade_task_run(task, cluster);
32 : * upgrade_task_free(task);
33 : * }
34 : *
35 : * Note that multiple steps can be added to a given task. When there are
36 : * multiple steps, the task will run all of the steps consecutively in the same
37 : * database connection before freeing the connection and moving on. In other
38 : * words, it only ever initiates one connection to each database in the
39 : * cluster for a given run.
40 : *
41 : * Copyright (c) 2024-2026, PostgreSQL Global Development Group
42 : * src/bin/pg_upgrade/task.c
43 : */
44 :
45 : #include "postgres_fe.h"
46 :
47 : #include "common/connect.h"
48 : #include "fe_utils/string_utils.h"
49 : #include "pg_upgrade.h"
50 :
51 : /*
52 : * dbs_complete stores the number of databases that we have completed
53 : * processing. When this value equals the number of databases in the cluster,
54 : * the task is finished.
55 : */
56 : static int dbs_complete;
57 :
58 : /*
59 : * dbs_processing stores the index of the next database in the cluster's array
60 : * of databases that will be picked up for processing. It will always be
61 : * greater than or equal to dbs_complete.
62 : */
63 : static int dbs_processing;
64 :
65 : /*
66 : * This struct stores the information for a single step of a task. Note that
67 : * the query string is stored in the "queries" PQExpBuffer for the UpgradeTask.
68 : * All steps in a task are run in a single connection before moving on to the
69 : * next database (which requires a new connection).
70 : */
71 : typedef struct UpgradeTaskStep
72 : {
73 : UpgradeTaskProcessCB process_cb; /* processes the results of the query */
74 : bool free_result; /* should we free the result? */
75 : void *arg; /* pointer passed to process_cb */
76 : } UpgradeTaskStep;
77 :
78 : /*
79 : * This struct is a thin wrapper around an array of steps, i.e.,
80 : * UpgradeTaskStep, plus a PQExpBuffer for all the query strings.
81 : */
82 : struct UpgradeTask
83 : {
84 : UpgradeTaskStep *steps;
85 : int num_steps;
86 : PQExpBuffer queries;
87 : };
88 :
89 : /*
90 : * The different states for a parallel slot.
91 : */
92 : typedef enum UpgradeTaskSlotState
93 : {
94 : FREE, /* slot available for use in a new database */
95 : CONNECTING, /* waiting for connection to be established */
96 : RUNNING_QUERIES, /* running/processing queries in the task */
97 : } UpgradeTaskSlotState;
98 :
99 : /*
100 : * We maintain an array of user_opts.jobs slots to execute the task.
101 : */
102 : typedef struct UpgradeTaskSlot
103 : {
104 : UpgradeTaskSlotState state; /* state of the slot */
105 : int db_idx; /* index of the database assigned to slot */
106 : int step_idx; /* index of the current step of task */
107 : PGconn *conn; /* current connection managed by slot */
108 : bool ready; /* slot is ready for processing */
109 : bool select_mode; /* select() mode: true->read, false->write */
110 : int sock; /* file descriptor for connection's socket */
111 : } UpgradeTaskSlot;
112 :
113 : /*
114 : * Initializes an UpgradeTask.
115 : */
116 : UpgradeTask *
117 0 : upgrade_task_create(void)
118 : {
119 0 : UpgradeTask *task = pg_malloc0(sizeof(UpgradeTask));
120 :
121 0 : task->queries = createPQExpBuffer();
122 :
123 : /* All tasks must first set a secure search_path. */
124 0 : upgrade_task_add_step(task, ALWAYS_SECURE_SEARCH_PATH_SQL, NULL, true, NULL);
125 :
126 0 : return task;
127 0 : }
128 :
129 : /*
130 : * Frees all storage associated with an UpgradeTask.
131 : */
132 : void
133 0 : upgrade_task_free(UpgradeTask *task)
134 : {
135 0 : destroyPQExpBuffer(task->queries);
136 0 : pg_free(task->steps);
137 0 : pg_free(task);
138 0 : }
139 :
140 : /*
141 : * Adds a step to an UpgradeTask. The steps will be executed in each database
142 : * in the order in which they are added.
143 : *
144 : * task: task object that must have been initialized via upgrade_task_create()
145 : * query: the query text
146 : * process_cb: function that processes the results of the query
147 : * free_result: should we free the PGresult, or leave it to the caller?
148 : * arg: pointer to task-specific data that is passed to each callback
149 : */
150 : void
151 0 : upgrade_task_add_step(UpgradeTask *task, const char *query,
152 : UpgradeTaskProcessCB process_cb, bool free_result,
153 : void *arg)
154 : {
155 0 : UpgradeTaskStep *new_step;
156 :
157 0 : task->steps = pg_realloc(task->steps,
158 0 : ++task->num_steps * sizeof(UpgradeTaskStep));
159 :
160 0 : new_step = &task->steps[task->num_steps - 1];
161 0 : new_step->process_cb = process_cb;
162 0 : new_step->free_result = free_result;
163 0 : new_step->arg = arg;
164 :
165 0 : appendPQExpBuffer(task->queries, "%s;", query);
166 0 : }
167 :
168 : /*
169 : * Build a connection string for the slot's current database and asynchronously
170 : * start a new connection, but do not wait for the connection to be
171 : * established.
172 : */
173 : static void
174 0 : start_conn(const ClusterInfo *cluster, UpgradeTaskSlot *slot)
175 : {
176 0 : PQExpBufferData conn_opts;
177 0 : DbInfo *dbinfo = &cluster->dbarr.dbs[slot->db_idx];
178 :
179 : /* Build connection string with proper quoting */
180 0 : initPQExpBuffer(&conn_opts);
181 0 : appendPQExpBufferStr(&conn_opts, "dbname=");
182 0 : appendConnStrVal(&conn_opts, dbinfo->db_name);
183 0 : appendPQExpBufferStr(&conn_opts, " user=");
184 0 : appendConnStrVal(&conn_opts, os_info.user);
185 0 : appendPQExpBuffer(&conn_opts, " port=%d", cluster->port);
186 0 : if (cluster->sockdir)
187 : {
188 0 : appendPQExpBufferStr(&conn_opts, " host=");
189 0 : appendConnStrVal(&conn_opts, cluster->sockdir);
190 0 : }
191 :
192 0 : slot->conn = PQconnectStart(conn_opts.data);
193 :
194 0 : if (!slot->conn)
195 0 : pg_fatal("out of memory");
196 :
197 0 : termPQExpBuffer(&conn_opts);
198 0 : }
199 :
200 : /*
201 : * Run the process_cb callback function to process the result of a query, and
202 : * free the result if the caller indicated we should do so.
203 : */
204 : static void
205 0 : process_query_result(const ClusterInfo *cluster, UpgradeTaskSlot *slot,
206 : const UpgradeTask *task)
207 : {
208 0 : UpgradeTaskStep *steps = &task->steps[slot->step_idx];
209 0 : UpgradeTaskProcessCB process_cb = steps->process_cb;
210 0 : DbInfo *dbinfo = &cluster->dbarr.dbs[slot->db_idx];
211 0 : PGresult *res = PQgetResult(slot->conn);
212 :
213 0 : if (PQstatus(slot->conn) == CONNECTION_BAD ||
214 0 : (PQresultStatus(res) != PGRES_TUPLES_OK &&
215 0 : PQresultStatus(res) != PGRES_COMMAND_OK))
216 0 : pg_fatal("connection failure: %s", PQerrorMessage(slot->conn));
217 :
218 : /*
219 : * We assume that a NULL process_cb callback function means there's
220 : * nothing to process. This is primarily intended for the initial step in
221 : * every task that sets a safe search_path.
222 : */
223 0 : if (process_cb)
224 0 : (*process_cb) (dbinfo, res, steps->arg);
225 :
226 0 : if (steps->free_result)
227 0 : PQclear(res);
228 0 : }
229 :
230 : /*
231 : * Advances the state machine for a given slot as necessary.
232 : */
233 : static void
234 0 : process_slot(const ClusterInfo *cluster, UpgradeTaskSlot *slot, const UpgradeTask *task)
235 : {
236 0 : PostgresPollingStatusType status;
237 :
238 0 : if (!slot->ready)
239 0 : return;
240 :
241 0 : switch (slot->state)
242 : {
243 : case FREE:
244 :
245 : /*
246 : * If all of the databases in the cluster have been processed or
247 : * are currently being processed by other slots, we are done.
248 : */
249 0 : if (dbs_processing >= cluster->dbarr.ndbs)
250 0 : return;
251 :
252 : /*
253 : * Claim the next database in the cluster's array and initiate a
254 : * new connection.
255 : */
256 0 : slot->db_idx = dbs_processing++;
257 0 : slot->state = CONNECTING;
258 0 : start_conn(cluster, slot);
259 :
260 0 : return;
261 :
262 : case CONNECTING:
263 :
264 : /* Check for connection failure. */
265 0 : status = PQconnectPoll(slot->conn);
266 0 : if (status == PGRES_POLLING_FAILED)
267 0 : pg_fatal("connection failure: %s", PQerrorMessage(slot->conn));
268 :
269 : /* Check whether the connection is still establishing. */
270 0 : if (status != PGRES_POLLING_OK)
271 : {
272 0 : slot->select_mode = (status == PGRES_POLLING_READING);
273 0 : return;
274 : }
275 :
276 : /*
277 : * Move on to running/processing the queries in the task.
278 : */
279 0 : slot->state = RUNNING_QUERIES;
280 0 : slot->select_mode = true; /* wait until ready for reading */
281 0 : if (!PQsendQuery(slot->conn, task->queries->data))
282 0 : pg_fatal("connection failure: %s", PQerrorMessage(slot->conn));
283 :
284 0 : return;
285 :
286 : case RUNNING_QUERIES:
287 :
288 : /*
289 : * Consume any available data and clear the read-ready indicator
290 : * for the connection.
291 : */
292 0 : if (!PQconsumeInput(slot->conn))
293 0 : pg_fatal("connection failure: %s", PQerrorMessage(slot->conn));
294 :
295 : /*
296 : * Process any results that are ready so that we can free up this
297 : * slot for another database as soon as possible.
298 : */
299 0 : for (; slot->step_idx < task->num_steps; slot->step_idx++)
300 : {
301 : /* If no more results are available yet, move on. */
302 0 : if (PQisBusy(slot->conn))
303 0 : return;
304 :
305 0 : process_query_result(cluster, slot, task);
306 0 : }
307 :
308 : /*
309 : * If we just finished processing the result of the last step in
310 : * the task, free the slot. We recursively call this function on
311 : * the newly-freed slot so that we can start initiating the next
312 : * connection immediately instead of waiting for the next loop
313 : * through the slots.
314 : */
315 0 : dbs_complete++;
316 0 : PQfinish(slot->conn);
317 0 : memset(slot, 0, sizeof(UpgradeTaskSlot));
318 0 : slot->ready = true;
319 :
320 0 : process_slot(cluster, slot, task);
321 :
322 0 : return;
323 : }
324 0 : }
325 :
326 : /*
327 : * Returns -1 on error, else the number of ready descriptors.
328 : */
329 : static int
330 0 : select_loop(int maxFd, fd_set *input, fd_set *output)
331 : {
332 0 : fd_set save_input = *input;
333 0 : fd_set save_output = *output;
334 :
335 0 : if (maxFd == 0)
336 0 : return 0;
337 :
338 0 : for (;;)
339 : {
340 0 : int i;
341 :
342 0 : *input = save_input;
343 0 : *output = save_output;
344 :
345 0 : i = select(maxFd + 1, input, output, NULL, NULL);
346 :
347 : #ifndef WIN32
348 0 : if (i < 0 && errno == EINTR)
349 0 : continue;
350 : #else
351 : if (i == SOCKET_ERROR && WSAGetLastError() == WSAEINTR)
352 : continue;
353 : #endif
354 0 : return i;
355 0 : }
356 0 : }
357 :
358 : /*
359 : * Wait on the slots to either finish connecting or to receive query results if
360 : * possible. This avoids a tight loop in upgrade_task_run().
361 : */
362 : static void
363 0 : wait_on_slots(UpgradeTaskSlot *slots, int numslots)
364 : {
365 0 : fd_set input;
366 0 : fd_set output;
367 0 : int maxFd = 0;
368 :
369 0 : FD_ZERO(&input);
370 0 : FD_ZERO(&output);
371 :
372 0 : for (int i = 0; i < numslots; i++)
373 : {
374 : /*
375 : * We assume the previous call to process_slot() handled everything
376 : * that was marked ready in the previous call to wait_on_slots(), if
377 : * any.
378 : */
379 0 : slots[i].ready = false;
380 :
381 : /*
382 : * This function should only ever see free slots as we are finishing
383 : * processing the last few databases, at which point we don't have any
384 : * databases left for them to process. We'll never use these slots
385 : * again, so we can safely ignore them.
386 : */
387 0 : if (slots[i].state == FREE)
388 0 : continue;
389 :
390 : /*
391 : * Add the socket to the set.
392 : */
393 0 : slots[i].sock = PQsocket(slots[i].conn);
394 0 : if (slots[i].sock < 0)
395 0 : pg_fatal("invalid socket");
396 0 : FD_SET(slots[i].sock, slots[i].select_mode ? &input : &output);
397 0 : maxFd = Max(maxFd, slots[i].sock);
398 0 : }
399 :
400 : /*
401 : * If we found socket(s) to wait on, wait.
402 : */
403 0 : if (select_loop(maxFd, &input, &output) == -1)
404 0 : pg_fatal("%s() failed: %m", "select");
405 :
406 : /*
407 : * Mark which sockets appear to be ready.
408 : */
409 0 : for (int i = 0; i < numslots; i++)
410 0 : slots[i].ready |= (FD_ISSET(slots[i].sock, &input) ||
411 0 : FD_ISSET(slots[i].sock, &output));
412 0 : }
413 :
414 : /*
415 : * Runs all the steps of the task in every database in the cluster using
416 : * user_opts.jobs parallel slots.
417 : */
418 : void
419 0 : upgrade_task_run(const UpgradeTask *task, const ClusterInfo *cluster)
420 : {
421 0 : int jobs = Max(1, user_opts.jobs);
422 0 : UpgradeTaskSlot *slots = pg_malloc0(sizeof(UpgradeTaskSlot) * jobs);
423 :
424 0 : dbs_complete = 0;
425 0 : dbs_processing = 0;
426 :
427 : /*
428 : * Process every slot the first time round.
429 : */
430 0 : for (int i = 0; i < jobs; i++)
431 0 : slots[i].ready = true;
432 :
433 0 : while (dbs_complete < cluster->dbarr.ndbs)
434 : {
435 0 : for (int i = 0; i < jobs; i++)
436 0 : process_slot(cluster, &slots[i], task);
437 :
438 0 : wait_on_slots(slots, jobs);
439 : }
440 :
441 0 : pg_free(slots);
442 0 : }
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