about summary refs log tree commit diff
path: root/db2/mp/mp_fget.c
blob: f159dc2d3e2468f6ea31d5a2e83c19d39a302332 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *	Sleepycat Software.  All rights reserved.
 */
#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)mp_fget.c	10.53 (Sleepycat) 11/16/98";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <errno.h>
#include <string.h>
#endif

#include "db_int.h"
#include "shqueue.h"
#include "db_shash.h"
#include "mp.h"
#include "common_ext.h"

/*
 * memp_fget --
 *	Get a page from the file.
 */
int
memp_fget(dbmfp, pgnoaddr, flags, addrp)
	DB_MPOOLFILE *dbmfp;
	db_pgno_t *pgnoaddr;
	u_int32_t flags;
	void *addrp;
{
	BH *bhp;
	DB_MPOOL *dbmp;
	MPOOL *mp;
	MPOOLFILE *mfp;
	size_t bucket, mf_offset;
	u_int32_t st_hsearch;
	int b_incr, first, ret;

	dbmp = dbmfp->dbmp;
	mp = dbmp->mp;
	mfp = dbmfp->mfp;

	MP_PANIC_CHECK(dbmp);

	/*
	 * Validate arguments.
	 *
	 * !!!
	 * Don't test for DB_MPOOL_CREATE and DB_MPOOL_NEW flags for readonly
	 * files here, and create non-existent pages in readonly files if the
	 * flags are set, later.  The reason is that the hash access method
	 * wants to get empty pages that don't really exist in readonly files.
	 * The only alternative is for hash to write the last "bucket" all the
	 * time, which we don't want to do because one of our big goals in life
	 * is to keep database files small.  It's sleazy as hell, but we catch
	 * any attempt to actually write the file in memp_fput().
	 */
#define	OKFLAGS	(DB_MPOOL_CREATE | DB_MPOOL_LAST | DB_MPOOL_NEW)
	if (flags != 0) {
		if ((ret =
		    __db_fchk(dbmp->dbenv, "memp_fget", flags, OKFLAGS)) != 0)
			return (ret);

		switch (flags) {
		case DB_MPOOL_CREATE:
		case DB_MPOOL_LAST:
		case DB_MPOOL_NEW:
		case 0:
			break;
		default:
			return (__db_ferr(dbmp->dbenv, "memp_fget", 1));
		}
	}

#ifdef DIAGNOSTIC
	/*
	 * XXX
	 * We want to switch threads as often as possible.  Yield every time
	 * we get a new page to ensure contention.
	 */
	if (DB_GLOBAL(db_pageyield))
		__os_yield(1);
#endif

	/* Initialize remaining local variables. */
	mf_offset = R_OFFSET(dbmp, mfp);
	bhp = NULL;
	st_hsearch = 0;
	b_incr = ret = 0;

	/* Determine the hash bucket where this page will live. */
	bucket = BUCKET(mp, mf_offset, *pgnoaddr);

	LOCKREGION(dbmp);

	/*
	 * Check for the last or last + 1 page requests.
	 *
	 * Examine and update the file's last_pgno value.  We don't care if
	 * the last_pgno value immediately changes due to another thread --
	 * at this instant in time, the value is correct.  We do increment the
	 * current last_pgno value if the thread is asking for a new page,
	 * however, to ensure that two threads creating pages don't get the
	 * same one.
	 */
	if (LF_ISSET(DB_MPOOL_LAST | DB_MPOOL_NEW)) {
		if (LF_ISSET(DB_MPOOL_NEW))
			++mfp->last_pgno;
		*pgnoaddr = mfp->last_pgno;
		bucket = BUCKET(mp, mf_offset, mfp->last_pgno);

		if (LF_ISSET(DB_MPOOL_NEW))
			goto alloc;
	}

	/*
	 * If mmap'ing the file and the page is not past the end of the file,
	 * just return a pointer.
	 *
	 * The page may be past the end of the file, so check the page number
	 * argument against the original length of the file.  If we previously
	 * returned pages past the original end of the file, last_pgno will
	 * have been updated to match the "new" end of the file, and checking
	 * against it would return pointers past the end of the mmap'd region.
	 *
	 * If another process has opened the file for writing since we mmap'd
	 * it, we will start playing the game by their rules, i.e. everything
	 * goes through the cache.  All pages previously returned will be safe,
	 * as long as the correct locking protocol was observed.
	 *
	 * XXX
	 * We don't discard the map because we don't know when all of the
	 * pages will have been discarded from the process' address space.
	 * It would be possible to do so by reference counting the open
	 * pages from the mmap, but it's unclear to me that it's worth it.
	 */
	if (dbmfp->addr != NULL && F_ISSET(mfp, MP_CAN_MMAP)) {
		if (*pgnoaddr > mfp->orig_last_pgno) {
			/*
			 * !!!
			 * See the comment above about non-existent pages and
			 * the hash access method.
			 */
			if (!LF_ISSET(DB_MPOOL_CREATE)) {
				__db_err(dbmp->dbenv,
				    "%s: page %lu doesn't exist",
				    __memp_fn(dbmfp), (u_long)*pgnoaddr);
				ret = EINVAL;
				goto err;
			}
		} else {
			*(void **)addrp =
			    R_ADDR(dbmfp, *pgnoaddr * mfp->stat.st_pagesize);
			++mp->stat.st_map;
			++mfp->stat.st_map;
			goto done;
		}
	}

	/* Search the hash chain for the page. */
	for (bhp = SH_TAILQ_FIRST(&dbmp->htab[bucket], __bh);
	    bhp != NULL; bhp = SH_TAILQ_NEXT(bhp, hq, __bh)) {
		++st_hsearch;
		if (bhp->pgno != *pgnoaddr || bhp->mf_offset != mf_offset)
			continue;

		/* Increment the reference count. */
		if (bhp->ref == UINT16_T_MAX) {
			__db_err(dbmp->dbenv,
			    "%s: page %lu: reference count overflow",
			    __memp_fn(dbmfp), (u_long)bhp->pgno);
			ret = EINVAL;
			goto err;
		}

		/*
		 * Increment the reference count.  We may discard the region
		 * lock as we evaluate and/or read the buffer, so we need to
		 * ensure that it doesn't move and that its contents remain
		 * unchanged.
		 */
		++bhp->ref;
		b_incr = 1;

		/*
	 	 * Any buffer we find might be trouble.
		 *
		 * BH_LOCKED --
		 * I/O is in progress.  Because we've incremented the buffer
		 * reference count, we know the buffer can't move.  Unlock
		 * the region lock, wait for the I/O to complete, and reacquire
		 * the region.
		 */
		for (first = 1; F_ISSET(bhp, BH_LOCKED); first = 0) {
			UNLOCKREGION(dbmp);

			/*
			 * Explicitly yield the processor if it's not the first
			 * pass through this loop -- if we don't, we might end
			 * up running to the end of our CPU quantum as we will
			 * simply be swapping between the two locks.
			 */
			if (!first)
				__os_yield(1);

			LOCKBUFFER(dbmp, bhp);
			/* Wait for I/O to finish... */
			UNLOCKBUFFER(dbmp, bhp);
			LOCKREGION(dbmp);
		}

		/*
		 * BH_TRASH --
		 * The contents of the buffer are garbage.  Shouldn't happen,
		 * and this read is likely to fail, but might as well try.
		 */
		if (F_ISSET(bhp, BH_TRASH))
			goto reread;

		/*
		 * BH_CALLPGIN --
		 * The buffer was converted so it could be written, and the
		 * contents need to be converted again.
		 */
		if (F_ISSET(bhp, BH_CALLPGIN)) {
			if ((ret = __memp_pg(dbmfp, bhp, 1)) != 0)
				goto err;
			F_CLR(bhp, BH_CALLPGIN);
		}

		++mp->stat.st_cache_hit;
		++mfp->stat.st_cache_hit;
		*(void **)addrp = bhp->buf;
		goto done;
	}

alloc:	/* Allocate new buffer header and data space. */
	if ((ret = __memp_alloc(dbmp, sizeof(BH) -
	    sizeof(u_int8_t) + mfp->stat.st_pagesize, NULL, &bhp)) != 0)
		goto err;

#ifdef DIAGNOSTIC
	if ((ALIGNTYPE)bhp->buf & (sizeof(size_t) - 1)) {
		__db_err(dbmp->dbenv,
		    "Internal error: BH data NOT size_t aligned.");
		ret = EINVAL;
		goto err;
	}
#endif
	/* Initialize the BH fields. */
	memset(bhp, 0, sizeof(BH));
	LOCKINIT(dbmp, &bhp->mutex);
	bhp->ref = 1;
	bhp->pgno = *pgnoaddr;
	bhp->mf_offset = mf_offset;

	/*
	 * Prepend the bucket header to the head of the appropriate MPOOL
	 * bucket hash list.  Append the bucket header to the tail of the
	 * MPOOL LRU chain.
	 */
	SH_TAILQ_INSERT_HEAD(&dbmp->htab[bucket], bhp, hq, __bh);
	SH_TAILQ_INSERT_TAIL(&mp->bhq, bhp, q);

	/*
	 * If we created the page, zero it out and continue.
	 *
	 * !!!
	 * Note: DB_MPOOL_NEW specifically doesn't call the pgin function.
	 * If DB_MPOOL_CREATE is used, then the application's pgin function
	 * has to be able to handle pages of 0's -- if it uses DB_MPOOL_NEW,
	 * it can detect all of its page creates, and not bother.
	 *
	 * Otherwise, read the page into memory, optionally creating it if
	 * DB_MPOOL_CREATE is set.
	 */
	if (LF_ISSET(DB_MPOOL_NEW)) {
		if (mfp->clear_len == 0)
			memset(bhp->buf, 0, mfp->stat.st_pagesize);
		else {
			memset(bhp->buf, 0, mfp->clear_len);
#ifdef DIAGNOSTIC
			memset(bhp->buf + mfp->clear_len, 0xdb,
			    mfp->stat.st_pagesize - mfp->clear_len);
#endif
		}

		++mp->stat.st_page_create;
		++mfp->stat.st_page_create;
	} else {
		/*
		 * It's possible for the read function to fail, which means
		 * that we fail as well.  Note, the __memp_pgread() function
		 * discards the region lock, so the buffer must be pinned
		 * down so that it cannot move and its contents are unchanged.
		 */
reread:		if ((ret = __memp_pgread(dbmfp,
		    bhp, LF_ISSET(DB_MPOOL_CREATE))) != 0) {
			/*
			 * !!!
			 * Discard the buffer unless another thread is waiting
			 * on our I/O to complete.  Regardless, the header has
			 * the BH_TRASH flag set.
			 */
			if (bhp->ref == 1)
				__memp_bhfree(dbmp, mfp, bhp, 1);
			goto err;
		}

		++mp->stat.st_cache_miss;
		++mfp->stat.st_cache_miss;
	}

	/*
	 * If we're returning a page after our current notion of the last-page,
	 * update our information.  Note, there's no way to un-instantiate this
	 * page, it's going to exist whether it's returned to us dirty or not.
	 */
	if (bhp->pgno > mfp->last_pgno)
		mfp->last_pgno = bhp->pgno;

	++mp->stat.st_page_clean;
	*(void **)addrp = bhp->buf;

done:	/* Update the chain search statistics. */
	if (st_hsearch) {
		++mp->stat.st_hash_searches;
		if (st_hsearch > mp->stat.st_hash_longest)
			mp->stat.st_hash_longest = st_hsearch;
		mp->stat.st_hash_examined += st_hsearch;
	}

	++dbmfp->pinref;

	UNLOCKREGION(dbmp);

	return (0);

err:	/* Discard our reference. */
	if (b_incr)
		--bhp->ref;
	UNLOCKREGION(dbmp);

	*(void **)addrp = NULL;
	return (ret);
}