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comparison items.c @ 0:30782bb1fc04 MEMCACHED_1_2_3

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memcached-1.2.3
author Maxim Dounin <mdounin@mdounin.ru>
date Sun, 23 Sep 2007 03:58:34 +0400
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1 /* -*- Mode: C; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */
2 /* $Id: items.c 551 2007-05-07 21:24:31Z plindner $ */
3 #include "memcached.h"
4 #include <sys/stat.h>
5 #include <sys/socket.h>
6 #include <sys/signal.h>
7 #include <sys/resource.h>
8 #include <fcntl.h>
9 #include <netinet/in.h>
10 #include <errno.h>
11 #include <stdlib.h>
12 #include <stdio.h>
13 #include <string.h>
14 #include <time.h>
15 #include <assert.h>
16
17 /* Forward Declarations */
18 static void item_link_q(item *it);
19 static void item_unlink_q(item *it);
20
21 /*
22 * We only reposition items in the LRU queue if they haven't been repositioned
23 * in this many seconds. That saves us from churning on frequently-accessed
24 * items.
25 */
26 #define ITEM_UPDATE_INTERVAL 60
27
28 #define LARGEST_ID 255
29 static item *heads[LARGEST_ID];
30 static item *tails[LARGEST_ID];
31 static unsigned int sizes[LARGEST_ID];
32
33 void item_init(void) {
34 int i;
35 for(i = 0; i < LARGEST_ID; i++) {
36 heads[i] = NULL;
37 tails[i] = NULL;
38 sizes[i] = 0;
39 }
40 }
41
42 /* Enable this for reference-count debugging. */
43 #if 0
44 # define DEBUG_REFCNT(it,op) \
45 fprintf(stderr, "item %x refcnt(%c) %d %c%c%c\n", \
46 it, op, it->refcount, \
47 (it->it_flags & ITEM_LINKED) ? 'L' : ' ', \
48 (it->it_flags & ITEM_SLABBED) ? 'S' : ' ', \
49 (it->it_flags & ITEM_DELETED) ? 'D' : ' ')
50 #else
51 # define DEBUG_REFCNT(it,op) while(0)
52 #endif
53
54 /*
55 * Generates the variable-sized part of the header for an object.
56 *
57 * key - The key
58 * nkey - The length of the key
59 * flags - key flags
60 * nbytes - Number of bytes to hold value and addition CRLF terminator
61 * suffix - Buffer for the "VALUE" line suffix (flags, size).
62 * nsuffix - The length of the suffix is stored here.
63 *
64 * Returns the total size of the header.
65 */
66 static size_t item_make_header(const uint8_t nkey, const int flags, const int nbytes,
67 char *suffix, uint8_t *nsuffix) {
68 /* suffix is defined at 40 chars elsewhere.. */
69 *nsuffix = (uint8_t) snprintf(suffix, 40, " %d %d\r\n", flags, nbytes - 2);
70 return sizeof(item) + nkey + *nsuffix + nbytes;
71 }
72
73 /*@null@*/
74 item *do_item_alloc(char *key, const size_t nkey, const int flags, const rel_time_t exptime, const int nbytes) {
75 uint8_t nsuffix;
76 item *it;
77 char suffix[40];
78 size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix);
79
80 unsigned int id = slabs_clsid(ntotal);
81 if (id == 0)
82 return 0;
83
84 it = slabs_alloc(ntotal);
85 if (it == 0) {
86 int tries = 50;
87 item *search;
88
89 /* If requested to not push old items out of cache when memory runs out,
90 * we're out of luck at this point...
91 */
92
93 if (settings.evict_to_free == 0) return NULL;
94
95 /*
96 * try to get one off the right LRU
97 * don't necessariuly unlink the tail because it may be locked: refcount>0
98 * search up from tail an item with refcount==0 and unlink it; give up after 50
99 * tries
100 */
101
102 if (id > LARGEST_ID) return NULL;
103 if (tails[id] == 0) return NULL;
104
105 for (search = tails[id]; tries > 0 && search != NULL; tries--, search=search->prev) {
106 if (search->refcount == 0) {
107 if (search->exptime > current_time) {
108 STATS_LOCK();
109 stats.evictions++;
110 STATS_UNLOCK();
111 }
112 do_item_unlink(search);
113 break;
114 }
115 }
116 it = slabs_alloc(ntotal);
117 if (it == 0) return NULL;
118 }
119
120 assert(it->slabs_clsid == 0);
121
122 it->slabs_clsid = id;
123
124 assert(it != heads[it->slabs_clsid]);
125
126 it->next = it->prev = it->h_next = 0;
127 it->refcount = 1; /* the caller will have a reference */
128 DEBUG_REFCNT(it, '*');
129 it->it_flags = 0;
130 it->nkey = nkey;
131 it->nbytes = nbytes;
132 strcpy(ITEM_key(it), key);
133 it->exptime = exptime;
134 memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
135 it->nsuffix = nsuffix;
136 return it;
137 }
138
139 void item_free(item *it) {
140 size_t ntotal = ITEM_ntotal(it);
141 assert((it->it_flags & ITEM_LINKED) == 0);
142 assert(it != heads[it->slabs_clsid]);
143 assert(it != tails[it->slabs_clsid]);
144 assert(it->refcount == 0);
145
146 /* so slab size changer can tell later if item is already free or not */
147 it->slabs_clsid = 0;
148 it->it_flags |= ITEM_SLABBED;
149 DEBUG_REFCNT(it, 'F');
150 slabs_free(it, ntotal);
151 }
152
153 /*
154 * Returns true if an item will fit in the cache (its size does not exceed
155 * the maximum for a cache entry.)
156 */
157 bool item_size_ok(const size_t nkey, const int flags, const int nbytes) {
158 char prefix[40];
159 uint8_t nsuffix;
160
161 return slabs_clsid(item_make_header(nkey + 1, flags, nbytes,
162 prefix, &nsuffix)) != 0;
163 }
164
165 static void item_link_q(item *it) { /* item is the new head */
166 item **head, **tail;
167 /* always true, warns: assert(it->slabs_clsid <= LARGEST_ID); */
168 assert((it->it_flags & ITEM_SLABBED) == 0);
169
170 head = &heads[it->slabs_clsid];
171 tail = &tails[it->slabs_clsid];
172 assert(it != *head);
173 assert((*head && *tail) || (*head == 0 && *tail == 0));
174 it->prev = 0;
175 it->next = *head;
176 if (it->next) it->next->prev = it;
177 *head = it;
178 if (*tail == 0) *tail = it;
179 sizes[it->slabs_clsid]++;
180 return;
181 }
182
183 static void item_unlink_q(item *it) {
184 item **head, **tail;
185 /* always true, warns: assert(it->slabs_clsid <= LARGEST_ID); */
186 head = &heads[it->slabs_clsid];
187 tail = &tails[it->slabs_clsid];
188
189 if (*head == it) {
190 assert(it->prev == 0);
191 *head = it->next;
192 }
193 if (*tail == it) {
194 assert(it->next == 0);
195 *tail = it->prev;
196 }
197 assert(it->next != it);
198 assert(it->prev != it);
199
200 if (it->next) it->next->prev = it->prev;
201 if (it->prev) it->prev->next = it->next;
202 sizes[it->slabs_clsid]--;
203 return;
204 }
205
206 int do_item_link(item *it) {
207 assert((it->it_flags & (ITEM_LINKED|ITEM_SLABBED)) == 0);
208 assert(it->nbytes < 1048576);
209 it->it_flags |= ITEM_LINKED;
210 it->time = current_time;
211 assoc_insert(it);
212
213 STATS_LOCK();
214 stats.curr_bytes += ITEM_ntotal(it);
215 stats.curr_items += 1;
216 stats.total_items += 1;
217 STATS_UNLOCK();
218
219 item_link_q(it);
220
221 return 1;
222 }
223
224 void do_item_unlink(item *it) {
225 if ((it->it_flags & ITEM_LINKED) != 0) {
226 it->it_flags &= ~ITEM_LINKED;
227 STATS_LOCK();
228 stats.curr_bytes -= ITEM_ntotal(it);
229 stats.curr_items -= 1;
230 STATS_UNLOCK();
231 assoc_delete(ITEM_key(it), it->nkey);
232 item_unlink_q(it);
233 if (it->refcount == 0) item_free(it);
234 }
235 }
236
237 void do_item_remove(item *it) {
238 assert((it->it_flags & ITEM_SLABBED) == 0);
239 if (it->refcount != 0) {
240 it->refcount--;
241 DEBUG_REFCNT(it, '-');
242 }
243 assert((it->it_flags & ITEM_DELETED) == 0 || it->refcount != 0);
244 if (it->refcount == 0 && (it->it_flags & ITEM_LINKED) == 0) {
245 item_free(it);
246 }
247 }
248
249 void do_item_update(item *it) {
250 if (it->time < current_time - ITEM_UPDATE_INTERVAL) {
251 assert((it->it_flags & ITEM_SLABBED) == 0);
252
253 if (it->it_flags & ITEM_LINKED) {
254 item_unlink_q(it);
255 it->time = current_time;
256 item_link_q(it);
257 }
258 }
259 }
260
261 int do_item_replace(item *it, item *new_it) {
262 assert((it->it_flags & ITEM_SLABBED) == 0);
263
264 do_item_unlink(it);
265 return do_item_link(new_it);
266 }
267
268 /*@null@*/
269 char *item_cachedump(const unsigned int slabs_clsid, const unsigned int limit, unsigned int *bytes) {
270 int memlimit = 2097152; /* 2097152: (2 * 1024 * 1024) */
271 char *buffer;
272 unsigned int bufcurr;
273 item *it;
274 int len;
275 int shown = 0;
276 char temp[512];
277
278 if (slabs_clsid > LARGEST_ID) return NULL;
279 it = heads[slabs_clsid];
280
281 buffer = malloc((size_t)memlimit);
282 if (buffer == 0) return NULL;
283 bufcurr = 0;
284
285 while (it != NULL && (limit == 0 || shown < limit)) {
286 len = snprintf(temp, 512, "ITEM %s [%d b; %lu s]\r\n", ITEM_key(it), it->nbytes - 2, it->time + stats.started);
287 if (bufcurr + len + 6 > memlimit) /* 6 is END\r\n\0 */
288 break;
289 strcpy(buffer + bufcurr, temp);
290 bufcurr += len;
291 shown++;
292 it = it->next;
293 }
294
295 memcpy(buffer + bufcurr, "END\r\n", 6);
296 bufcurr += 5;
297
298 *bytes = bufcurr;
299 return buffer;
300 }
301
302 void item_stats(char *buffer, const int buflen) {
303 int i;
304 char *bufcurr = buffer;
305 rel_time_t now = current_time;
306
307 if (buflen < 4096) {
308 strcpy(buffer, "SERVER_ERROR out of memory");
309 return;
310 }
311
312 for (i = 0; i < LARGEST_ID; i++) {
313 if (tails[i] != NULL)
314 bufcurr += snprintf(bufcurr, (size_t)buflen, "STAT items:%d:number %u\r\nSTAT items:%d:age %u\r\n",
315 i, sizes[i], i, now - tails[i]->time);
316 }
317 memcpy(bufcurr, "END", 4);
318 return;
319 }
320
321 /* dumps out a list of objects of each size, with granularity of 32 bytes */
322 /*@null@*/
323 char* item_stats_sizes(int *bytes) {
324 const int num_buckets = 32768; /* max 1MB object, divided into 32 bytes size buckets */
325 unsigned int *histogram = (unsigned int *)malloc((size_t)num_buckets * sizeof(int));
326 char *buf = (char *)malloc(2097152 * sizeof(char)); /* 2097152: 2 * 1024 * 1024 */
327 int i;
328
329 if (histogram == 0 || buf == 0) {
330 if (histogram) free(histogram);
331 if (buf) free(buf);
332 return NULL;
333 }
334
335 /* build the histogram */
336 memset(histogram, 0, (size_t)num_buckets * sizeof(int));
337 for (i = 0; i < LARGEST_ID; i++) {
338 item *iter = heads[i];
339 while (iter) {
340 int ntotal = ITEM_ntotal(iter);
341 int bucket = ntotal / 32;
342 if ((ntotal % 32) != 0) bucket++;
343 if (bucket < num_buckets) histogram[bucket]++;
344 iter = iter->next;
345 }
346 }
347
348 /* write the buffer */
349 *bytes = 0;
350 for (i = 0; i < num_buckets; i++) {
351 if (histogram[i] != 0) {
352 *bytes += sprintf(&buf[*bytes], "%d %u\r\n", i * 32, histogram[i]);
353 }
354 }
355 *bytes += sprintf(&buf[*bytes], "END\r\n");
356 free(histogram);
357 return buf;
358 }
359
360 /* returns true if a deleted item's delete-locked-time is over, and it
361 should be removed from the namespace */
362 bool item_delete_lock_over (item *it) {
363 assert(it->it_flags & ITEM_DELETED);
364 return (current_time >= it->exptime);
365 }
366
367 /* wrapper around assoc_find which does the lazy expiration/deletion logic */
368 item *do_item_get_notedeleted(const char *key, const size_t nkey, bool *delete_locked) {
369 item *it = assoc_find(key, nkey);
370 if (delete_locked) *delete_locked = false;
371 if (it && (it->it_flags & ITEM_DELETED)) {
372 /* it's flagged as delete-locked. let's see if that condition
373 is past due, and the 5-second delete_timer just hasn't
374 gotten to it yet... */
375 if (!item_delete_lock_over(it)) {
376 if (delete_locked) *delete_locked = true;
377 it = 0;
378 }
379 }
380 if (it != NULL && settings.oldest_live != 0 && settings.oldest_live <= current_time &&
381 it->time <= settings.oldest_live) {
382 do_item_unlink(it); // MTSAFE - cache_lock held
383 it = 0;
384 }
385 if (it != NULL && it->exptime != 0 && it->exptime <= current_time) {
386 do_item_unlink(it); // MTSAFE - cache_lock held
387 it = 0;
388 }
389
390 if (it != NULL) {
391 it->refcount++;
392 DEBUG_REFCNT(it, '+');
393 }
394 return it;
395 }
396
397 item *item_get(const char *key, const size_t nkey) {
398 return item_get_notedeleted(key, nkey, 0);
399 }
400
401 /* returns an item whether or not it's delete-locked or expired. */
402 item *do_item_get_nocheck(const char *key, const size_t nkey) {
403 item *it = assoc_find(key, nkey);
404 if (it) {
405 it->refcount++;
406 DEBUG_REFCNT(it, '+');
407 }
408 return it;
409 }
410
411 /* expires items that are more recent than the oldest_live setting. */
412 void do_item_flush_expired(void) {
413 int i;
414 item *iter, *next;
415 if (settings.oldest_live == 0)
416 return;
417 for (i = 0; i < LARGEST_ID; i++) {
418 /* The LRU is sorted in decreasing time order, and an item's timestamp
419 * is never newer than its last access time, so we only need to walk
420 * back until we hit an item older than the oldest_live time.
421 * The oldest_live checking will auto-expire the remaining items.
422 */
423 for (iter = heads[i]; iter != NULL; iter = next) {
424 if (iter->time >= settings.oldest_live) {
425 next = iter->next;
426 if ((iter->it_flags & ITEM_SLABBED) == 0) {
427 do_item_unlink(iter);
428 }
429 } else {
430 /* We've hit the first old item. Continue to the next queue. */
431 break;
432 }
433 }
434 }
435 }