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GeezerVison is showing github.com — sqlcipher/src/pcache1.c at master · wolfcon/sqlcipher Expand file tree/ Copy pathpcache1.cMore file actions 1259 lines (1179 loc) · 41.4 KB / Copy pathpcache1.cFile metadata and controls1259 lines (1179 loc) · 41.4 KB 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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 /* ** 2008 November 05 ** ** The author disclaims copyright to this source code. In place of ** a legal notice, here is a blessing: ** ** May you do good and not evil. ** May you find forgiveness for yourself and forgive others. ** May you share freely, never taking more than you give. ** ************************************************************************* ** ** This file implements the default page cache implementation (the ** sqlite3_pcache interface). It also contains part of the implementation ** of the SQLITE_CONFIG_PAGECACHE and sqlite3_release_memory() features. ** If the default page cache implementation is overridden, then neither of ** these two features are available. ** ** A Page cache line looks like this: ** ** ------------------------------------------------------------- ** | database page content | PgHdr1 | MemPage | PgHdr | ** ------------------------------------------------------------- ** ** The database page content is up front (so that buffer overreads tend to ** flow harmlessly into the PgHdr1, MemPage, and PgHdr extensions). MemPage ** is the extension added by the btree.c module containing information such ** as the database page number and how that database page is used. PgHdr ** is added by the pcache.c layer and contains information used to keep track ** of which pages are "dirty". PgHdr1 is an extension added by this ** module (pcache1.c). The PgHdr1 header is a subclass of sqlite3_pcache_page. ** PgHdr1 contains information needed to look up a page by its page number. ** The superclass sqlite3_pcache_page.pBuf points to the start of the ** database page content and sqlite3_pcache_page.pExtra points to PgHdr. ** ** The size of the extension (MemPage+PgHdr+PgHdr1) can be determined at ** runtime using sqlite3_config(SQLITE_CONFIG_PCACHE_HDRSZ, &size). The ** sizes of the extensions sum to 272 bytes on x64 for 3.8.10, but this ** size can vary according to architecture, compile-time options, and ** SQLite library version number. ** ** If SQLITE_PCACHE_SEPARATE_HEADER is defined, then the extension is obtained ** using a separate memory allocation from the database page content. This ** seeks to overcome the "clownshoe" problem (also called "internal ** fragmentation" in academic literature) of allocating a few bytes more ** than a power of two with the memory allocator rounding up to the next ** power of two, and leaving the rounded-up space unused. ** ** This module tracks pointers to PgHdr1 objects. Only pcache.c communicates ** with this module. Information is passed back and forth as PgHdr1 pointers. ** ** The pcache.c and pager.c modules deal pointers to PgHdr objects. ** The btree.c module deals with pointers to MemPage objects. ** ** SOURCE OF PAGE CACHE MEMORY: ** ** Memory for a page might come from any of three sources: ** ** (1) The general-purpose memory allocator - sqlite3Malloc() ** (2) Global page-cache memory provided using sqlite3_config() with ** SQLITE_CONFIG_PAGECACHE. ** (3) PCache-local bulk allocation. ** ** The third case is a chunk of heap memory (defaulting to 100 pages worth) ** that is allocated when the page cache is created. The size of the local ** bulk allocation can be adjusted using ** ** sqlite3_config(SQLITE_CONFIG_PAGECACHE, (void*)0, 0, N). ** ** If N is positive, then N pages worth of memory are allocated using a single ** sqlite3Malloc() call and that memory is used for the first N pages allocated. ** Or if N is negative, then -1024*N bytes of memory are allocated and used ** for as many pages as can be accomodated. ** ** Only one of (2) or (3) can be used. Once the memory available to (2) or ** (3) is exhausted, subsequent allocations fail over to the general-purpose ** memory allocator (1). ** ** Earlier versions of SQLite used only methods (1) and (2). But experiments ** show that method (3) with N==100 provides about a 5% performance boost for ** common workloads. */ #include "sqliteInt.h" typedef struct PCache1 PCache1; typedef struct PgHdr1 PgHdr1; typedef struct PgFreeslot PgFreeslot; typedef struct PGroup PGroup; /* ** Each cache entry is represented by an instance of the following ** structure. Unless SQLITE_PCACHE_SEPARATE_HEADER is defined, a buffer of ** PgHdr1.pCache->szPage bytes is allocated directly before this structure ** in memory. */ struct PgHdr1 { sqlite3_pcache_page page; /* Base class. Must be first. pBuf & pExtra */ unsigned int iKey; /* Key value (page number) */ u8 isBulkLocal; /* This page from bulk local storage */ u8 isAnchor; /* This is the PGroup.lru element */ PgHdr1 *pNext; /* Next in hash table chain */ PCache1 *pCache; /* Cache that currently owns this page */ PgHdr1 *pLruNext; /* Next in LRU list of unpinned pages */ PgHdr1 *pLruPrev; /* Previous in LRU list of unpinned pages */ }; /* ** A page is pinned if it is not on the LRU list. To be "pinned" means ** that the page is in active use and must not be deallocated. */ #define PAGE_IS_PINNED(p) ((p)->pLruNext==0) #define PAGE_IS_UNPINNED(p) ((p)->pLruNext!=0) /* Each page cache (or PCache) belongs to a PGroup. A PGroup is a set ** of one or more PCaches that are able to recycle each other's unpinned ** pages when they are under memory pressure. A PGroup is an instance of ** the following object. ** ** This page cache implementation works in one of two modes: ** ** (1) Every PCache is the sole member of its own PGroup. There is ** one PGroup per PCache. ** ** (2) There is a single global PGroup that all PCaches are a member ** of. ** ** Mode 1 uses more memory (since PCache instances are not able to rob ** unused pages from other PCaches) but it also operates without a mutex, ** and is therefore often faster. Mode 2 requires a mutex in order to be ** threadsafe, but recycles pages more efficiently. ** ** For mode (1), PGroup.mutex is NULL. For mode (2) there is only a single ** PGroup which is the pcache1.grp global variable and its mutex is ** SQLITE_MUTEX_STATIC_LRU. */ struct PGroup { sqlite3_mutex *mutex; /* MUTEX_STATIC_LRU or NULL */ unsigned int nMaxPage; /* Sum of nMax for purgeable caches */ unsigned int nMinPage; /* Sum of nMin for purgeable caches */ unsigned int mxPinned; /* nMaxpage + 10 - nMinPage */ unsigned int nPurgeable; /* Number of purgeable pages allocated */ PgHdr1 lru; /* The beginning and end of the LRU list */ }; /* Each page cache is an instance of the following object. Every ** open database file (including each in-memory database and each ** temporary or transient database) has a single page cache which ** is an instance of this object. ** ** Pointers to structures of this type are cast and returned as ** opaque sqlite3_pcache* handles. */ struct PCache1 { /* Cache configuration parameters. Page size (szPage) and the purgeable ** flag (bPurgeable) and the pnPurgeable pointer are all set when the ** cache is created and are never changed thereafter. nMax may be ** modified at any time by a call to the pcache1Cachesize() method. ** The PGroup mutex must be held when accessing nMax. */ PGroup *pGroup; /* PGroup this cache belongs to */ unsigned int *pnPurgeable; /* Pointer to pGroup->nPurgeable */ int szPage; /* Size of database content section */ int szExtra; /* sizeof(MemPage)+sizeof(PgHdr) */ int szAlloc; /* Total size of one pcache line */ int bPurgeable; /* True if cache is purgeable */ unsigned int nMin; /* Minimum number of pages reserved */ unsigned int nMax; /* Configured "cache_size" value */ unsigned int n90pct; /* nMax*9/10 */ unsigned int iMaxKey; /* Largest key seen since xTruncate() */ /* Hash table of all pages. The following variables may only be accessed ** when the accessor is holding the PGroup mutex. */ unsigned int nRecyclable; /* Number of pages in the LRU list */ unsigned int nPage; /* Total number of pages in apHash */ unsigned int nHash; /* Number of slots in apHash[] */ PgHdr1 **apHash; /* Hash table for fast lookup by key */ PgHdr1 *pFree; /* List of unused pcache-local pages */ void *pBulk; /* Bulk memory used by pcache-local */ }; /* ** Free slots in the allocator used to divide up the global page cache ** buffer provided using the SQLITE_CONFIG_PAGECACHE mechanism. */ struct PgFreeslot { PgFreeslot *pNext; /* Next free slot */ }; /* ** Global data used by this cache. */ static SQLITE_WSD struct PCacheGlobal { PGroup grp; /* The global PGroup for mode (2) */ /* Variables related to SQLITE_CONFIG_PAGECACHE settings. The ** szSlot, nSlot, pStart, pEnd, nReserve, and isInit values are all ** fixed at sqlite3_initialize() time and do not require mutex protection. ** The nFreeSlot and pFree values do require mutex protection. */ int isInit; /* True if initialized */ int separateCache; /* Use a new PGroup for each PCache */ int nInitPage; /* Initial bulk allocation size */ int szSlot; /* Size of each free slot */ int nSlot; /* The number of pcache slots */ int nReserve; /* Try to keep nFreeSlot above this */ void *pStart, *pEnd; /* Bounds of global page cache memory */ /* Above requires no mutex. Use mutex below for variable that follow. */ sqlite3_mutex *mutex; /* Mutex for accessing the following: */ PgFreeslot *pFree; /* Free page blocks */ int nFreeSlot; /* Number of unused pcache slots */ /* The following value requires a mutex to change. We skip the mutex on ** reading because (1) most platforms read a 32-bit integer atomically and ** (2) even if an incorrect value is read, no great harm is done since this ** is really just an optimization. */ int bUnderPressure; /* True if low on PAGECACHE memory */ } pcache1_g; /* ** All code in this file should access the global structure above via the ** alias "pcache1". This ensures that the WSD emulation is used when ** compiling for systems that do not support real WSD. */ #define pcache1 (GLOBAL(struct PCacheGlobal, pcache1_g)) /* ** Macros to enter and leave the PCache LRU mutex. */ #if !defined(SQLITE_ENABLE_MEMORY_MANAGEMENT) || SQLITE_THREADSAFE==0 # define pcache1EnterMutex(X) assert((X)->mutex==0) # define pcache1LeaveMutex(X) assert((X)->mutex==0) # define PCACHE1_MIGHT_USE_GROUP_MUTEX 0 #else # define pcache1EnterMutex(X) sqlite3_mutex_enter((X)->mutex) # define pcache1LeaveMutex(X) sqlite3_mutex_leave((X)->mutex) # define PCACHE1_MIGHT_USE_GROUP_MUTEX 1 #endif /******************************************************************************/ /******** Page Allocation/SQLITE_CONFIG_PCACHE Related Functions **************/ /* ** This function is called during initialization if a static buffer is ** supplied to use for the page-cache by passing the SQLITE_CONFIG_PAGECACHE ** verb to sqlite3_config(). Parameter pBuf points to an allocation large ** enough to contain 'n' buffers of 'sz' bytes each. ** ** This routine is called from sqlite3_initialize() and so it is guaranteed ** to be serialized already. There is no need for further mutexing. */ void sqlite3PCacheBufferSetup(void *pBuf, int sz, int n){ if( pcache1.isInit ){ PgFreeslot *p; if( pBuf==0 ) sz = n = 0; if( n==0 ) sz = 0; sz = ROUNDDOWN8(sz); pcache1.szSlot = sz; pcache1.nSlot = pcache1.nFreeSlot = n; pcache1.nReserve = n>90 ? 10 : (n/10 + 1); pcache1.pStart = pBuf; pcache1.pFree = 0; pcache1.bUnderPressure = 0; while( n-- ){ p = (PgFreeslot*)pBuf; p->pNext = pcache1.pFree; pcache1.pFree = p; pBuf = (void*)&((char*)pBuf)[sz]; } pcache1.pEnd = pBuf; } } /* ** Try to initialize the pCache->pFree and pCache->pBulk fields. Return ** true if pCache->pFree ends up containing one or more free pages. */ static int pcache1InitBulk(PCache1 *pCache){ i64 szBulk; char *zBulk; if( pcache1.nInitPage==0 ) return 0; /* Do not bother with a bulk allocation if the cache size very small */ if( pCache->nMax<3 ) return 0; sqlite3BeginBenignMalloc(); if( pcache1.nInitPage>0 ){ szBulk = pCache->szAlloc * (i64)pcache1.nInitPage; }else{ szBulk = -1024 * (i64)pcache1.nInitPage; } if( szBulk > pCache->szAlloc*(i64)pCache->nMax ){ szBulk = pCache->szAlloc*(i64)pCache->nMax; } zBulk = pCache->pBulk = sqlite3Malloc( szBulk ); sqlite3EndBenignMalloc(); if( zBulk ){ int nBulk = sqlite3MallocSize(zBulk)/pCache->szAlloc; do{ PgHdr1 *pX = (PgHdr1*)&zBulk[pCache->szPage]; pX->page.pBuf = zBulk; pX->page.pExtra = &pX[1]; pX->isBulkLocal = 1; pX->isAnchor = 0; pX->pNext = pCache->pFree; pCache->pFree = pX; zBulk += pCache->szAlloc; }while( --nBulk ); } return pCache->pFree!=0; } /* ** Malloc function used within this file to allocate space from the buffer ** configured using sqlite3_config(SQLITE_CONFIG_PAGECACHE) option. If no ** such buffer exists or there is no space left in it, this function falls ** back to sqlite3Malloc(). ** ** Multiple threads can run this routine at the same time. Global variables ** in pcache1 need to be protected via mutex. */ static void *pcache1Alloc(int nByte){ void *p = 0; assert( sqlite3_mutex_notheld(pcache1.grp.mutex) ); if( nByte<=pcache1.szSlot ){ sqlite3_mutex_enter(pcache1.mutex); p = (PgHdr1 *)pcache1.pFree; if( p ){ pcache1.pFree = pcache1.pFree->pNext; pcache1.nFreeSlot--; pcache1.bUnderPressure = pcache1.nFreeSlot<pcache1.nReserve; assert( pcache1.nFreeSlot>=0 ); sqlite3StatusHighwater(SQLITE_STATUS_PAGECACHE_SIZE, nByte); sqlite3StatusUp(SQLITE_STATUS_PAGECACHE_USED, 1); } sqlite3_mutex_leave(pcache1.mutex); } if( p==0 ){ /* Memory is not available in the SQLITE_CONFIG_PAGECACHE pool. Get ** it from sqlite3Malloc instead. */ p = sqlite3Malloc(nByte); #ifndef SQLITE_DISABLE_PAGECACHE_OVERFLOW_STATS if( p ){ int sz = sqlite3MallocSize(p); sqlite3_mutex_enter(pcache1.mutex); sqlite3StatusHighwater(SQLITE_STATUS_PAGECACHE_SIZE, nByte); sqlite3StatusUp(SQLITE_STATUS_PAGECACHE_OVERFLOW, sz); sqlite3_mutex_leave(pcache1.mutex); } #endif sqlite3MemdebugSetType(p, MEMTYPE_PCACHE); } return p; } /* ** Free an allocated buffer obtained from pcache1Alloc(). */ static void pcache1Free(void *p){ if( p==0 ) return; if( SQLITE_WITHIN(p, pcache1.pStart, pcache1.pEnd) ){ PgFreeslot *pSlot; sqlite3_mutex_enter(pcache1.mutex); sqlite3StatusDown(SQLITE_STATUS_PAGECACHE_USED, 1); pSlot = (PgFreeslot*)p; pSlot->pNext = pcache1.pFree; pcache1.pFree = pSlot; pcache1.nFreeSlot++; pcache1.bUnderPressure = pcache1.nFreeSlot<pcache1.nReserve; assert( pcache1.nFreeSlot<=pcache1.nSlot ); sqlite3_mutex_leave(pcache1.mutex); }else{ assert( sqlite3MemdebugHasType(p, MEMTYPE_PCACHE) ); sqlite3MemdebugSetType(p, MEMTYPE_HEAP); #ifndef SQLITE_DISABLE_PAGECACHE_OVERFLOW_STATS { int nFreed = 0; nFreed = sqlite3MallocSize(p); sqlite3_mutex_enter(pcache1.mutex); sqlite3StatusDown(SQLITE_STATUS_PAGECACHE_OVERFLOW, nFreed); sqlite3_mutex_leave(pcache1.mutex); } #endif sqlite3_free(p); } } #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT /* ** Return the size of a pcache allocation */ static int pcache1MemSize(void *p){ if( p>=pcache1.pStart && p<pcache1.pEnd ){ return pcache1.szSlot; }else{ int iSize; assert( sqlite3MemdebugHasType(p, MEMTYPE_PCACHE) ); sqlite3MemdebugSetType(p, MEMTYPE_HEAP); iSize = sqlite3MallocSize(p); sqlite3MemdebugSetType(p, MEMTYPE_PCACHE); return iSize; } } #endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */ /* ** Allocate a new page object initially associated with cache pCache. */ static PgHdr1 *pcache1AllocPage(PCache1 *pCache, int benignMalloc){ PgHdr1 *p = 0; void *pPg; assert( sqlite3_mutex_held(pCache->pGroup->mutex) ); if( pCache->pFree || (pCache->nPage==0 && pcache1InitBulk(pCache)) ){ p = pCache->pFree; pCache->pFree = p->pNext; p->pNext = 0; }else{ #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT /* The group mutex must be released before pcache1Alloc() is called. This ** is because it might call sqlite3_release_memory(), which assumes that ** this mutex is not held. */ assert( pcache1.separateCache==0 ); assert( pCache->pGroup==&pcache1.grp ); pcache1LeaveMutex(pCache->pGroup); #endif if( benignMalloc ){ sqlite3BeginBenignMalloc(); } #ifdef SQLITE_PCACHE_SEPARATE_HEADER pPg = pcache1Alloc(pCache->szPage); p = sqlite3Malloc(sizeof(PgHdr1) + pCache->szExtra); if( !pPg || !p ){ pcache1Free(pPg); sqlite3_free(p); pPg = 0; } #else pPg = pcache1Alloc(pCache->szAlloc); p = (PgHdr1 *)&((u8 *)pPg)[pCache->szPage]; #endif if( benignMalloc ){ sqlite3EndBenignMalloc(); } #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT pcache1EnterMutex(pCache->pGroup); #endif if( pPg==0 ) return 0; p->page.pBuf = pPg; p->page.pExtra = &p[1]; p->isBulkLocal = 0; p->isAnchor = 0; } (*pCache->pnPurgeable)++; return p; } /* ** Free a page object allocated by pcache1AllocPage(). */ static void pcache1FreePage(PgHdr1 *p){ PCache1 *pCache; assert( p!=0 ); pCache = p->pCache; assert( sqlite3_mutex_held(p->pCache->pGroup->mutex) ); if( p->isBulkLocal ){ p->pNext = pCache->pFree; pCache->pFree = p; }else{ pcache1Free(p->page.pBuf); #ifdef SQLITE_PCACHE_SEPARATE_HEADER sqlite3_free(p); #endif } (*pCache->pnPurgeable)--; } /* ** Malloc function used by SQLite to obtain space from the buffer configured ** using sqlite3_config(SQLITE_CONFIG_PAGECACHE) option. If no such buffer ** exists, this function falls back to sqlite3Malloc(). */ void *sqlite3PageMalloc(int sz){ return pcache1Alloc(sz); } /* ** Free an allocated buffer obtained from sqlite3PageMalloc(). */ void sqlite3PageFree(void *p){ pcache1Free(p); } /* ** Return true if it desirable to avoid allocating a new page cache ** entry. ** ** If memory was allocated specifically to the page cache using ** SQLITE_CONFIG_PAGECACHE but that memory has all been used, then ** it is desirable to avoid allocating a new page cache entry because ** presumably SQLITE_CONFIG_PAGECACHE was suppose to be sufficient ** for all page cache needs and we should not need to spill the ** allocation onto the heap. ** ** Or, the heap is used for all page cache memory but the heap is ** under memory pressure, then again it is desirable to avoid ** allocating a new page cache entry in order to avoid stressing ** the heap even further. */ static int pcache1UnderMemoryPressure(PCache1 *pCache){ if( pcache1.nSlot && (pCache->szPage+pCache->szExtra)<=pcache1.szSlot ){ return pcache1.bUnderPressure; }else{ return sqlite3HeapNearlyFull(); } } /******************************************************************************/ /******** General Implementation Functions ************************************/ /* ** This function is used to resize the hash table used by the cache passed ** as the first argument. ** ** The PCache mutex must be held when this function is called. */ static void pcache1ResizeHash(PCache1 *p){ PgHdr1 **apNew; unsigned int nNew; unsigned int i; assert( sqlite3_mutex_held(p->pGroup->mutex) ); nNew = p->nHash*2; if( nNew<256 ){ nNew = 256; } pcache1LeaveMutex(p->pGroup); if( p->nHash ){ sqlite3BeginBenignMalloc(); } apNew = (PgHdr1 **)sqlite3MallocZero(sizeof(PgHdr1 *)*nNew); if( p->nHash ){ sqlite3EndBenignMalloc(); } pcache1EnterMutex(p->pGroup); if( apNew ){ for(i=0; i<p->nHash; i++){ PgHdr1 *pPage; PgHdr1 *pNext = p->apHash[i]; while( (pPage = pNext)!=0 ){ unsigned int h = pPage->iKey % nNew; pNext = pPage->pNext; pPage->pNext = apNew[h]; apNew[h] = pPage; } } sqlite3_free(p->apHash); p->apHash = apNew; p->nHash = nNew; } } /* ** This function is used internally to remove the page pPage from the ** PGroup LRU list, if is part of it. If pPage is not part of the PGroup ** LRU list, then this function is a no-op. ** ** The PGroup mutex must be held when this function is called. */ static PgHdr1 *pcache1PinPage(PgHdr1 *pPage){ assert( pPage!=0 ); assert( PAGE_IS_UNPINNED(pPage) ); assert( pPage->pLruNext ); assert( pPage->pLruPrev ); assert( sqlite3_mutex_held(pPage->pCache->pGroup->mutex) ); pPage->pLruPrev->pLruNext = pPage->pLruNext; pPage->pLruNext->pLruPrev = pPage->pLruPrev; pPage->pLruNext = 0; pPage->pLruPrev = 0; assert( pPage->isAnchor==0 ); assert( pPage->pCache->pGroup->lru.isAnchor==1 ); pPage->pCache->nRecyclable--; return pPage; } /* ** Remove the page supplied as an argument from the hash table ** (PCache1.apHash structure) that it is currently stored in. ** Also free the page if freePage is true. ** ** The PGroup mutex must be held when this function is called. */ static void pcache1RemoveFromHash(PgHdr1 *pPage, int freeFlag){ unsigned int h; PCache1 *pCache = pPage->pCache; PgHdr1 **pp; assert( sqlite3_mutex_held(pCache->pGroup->mutex) ); h = pPage->iKey % pCache->nHash; for(pp=&pCache->apHash[h]; (*pp)!=pPage; pp=&(*pp)->pNext); *pp = (*pp)->pNext; pCache->nPage--; if( freeFlag ) pcache1FreePage(pPage); } /* ** If there are currently more than nMaxPage pages allocated, try ** to recycle pages to reduce the number allocated to nMaxPage. */ static void pcache1EnforceMaxPage(PCache1 *pCache){ PGroup *pGroup = pCache->pGroup; PgHdr1 *p; assert( sqlite3_mutex_held(pGroup->mutex) ); while( pGroup->nPurgeable>pGroup->nMaxPage && (p=pGroup->lru.pLruPrev)->isAnchor==0 ){ assert( p->pCache->pGroup==pGroup ); assert( PAGE_IS_UNPINNED(p) ); pcache1PinPage(p); pcache1RemoveFromHash(p, 1); } if( pCache->nPage==0 && pCache->pBulk ){ sqlite3_free(pCache->pBulk); pCache->pBulk = pCache->pFree = 0; } } /* ** Discard all pages from cache pCache with a page number (key value) ** greater than or equal to iLimit. Any pinned pages that meet this ** criteria are unpinned before they are discarded. ** ** The PCache mutex must be held when this function is called. */ static void pcache1TruncateUnsafe( PCache1 *pCache, /* The cache to truncate */ unsigned int iLimit /* Drop pages with this pgno or larger */ ){ TESTONLY( int nPage = 0; ) /* To assert pCache->nPage is correct */ unsigned int h, iStop; assert( sqlite3_mutex_held(pCache->pGroup->mutex) ); assert( pCache->iMaxKey >= iLimit ); assert( pCache->nHash > 0 ); if( pCache->iMaxKey - iLimit < pCache->nHash ){ /* If we are just shaving the last few pages off the end of the ** cache, then there is no point in scanning the entire hash table. ** Only scan those hash slots that might contain pages that need to ** be removed. */ h = iLimit % pCache->nHash; iStop = pCache->iMaxKey % pCache->nHash; TESTONLY( nPage = -10; ) /* Disable the pCache->nPage validity check */ }else{ /* This is the general case where many pages are being removed. ** It is necessary to scan the entire hash table */ h = pCache->nHash/2; iStop = h - 1; } for(;;){ PgHdr1 **pp; PgHdr1 *pPage; assert( h<pCache->nHash ); pp = &pCache->apHash[h]; while( (pPage = *pp)!=0 ){ if( pPage->iKey>=iLimit ){ pCache->nPage--; *pp = pPage->pNext; if( PAGE_IS_UNPINNED(pPage) ) pcache1PinPage(pPage); pcache1FreePage(pPage); }else{ pp = &pPage->pNext; TESTONLY( if( nPage>=0 ) nPage++; ) } } if( h==iStop ) break; h = (h+1) % pCache->nHash; } assert( nPage<0 || pCache->nPage==(unsigned)nPage ); } /******************************************************************************/ /******** sqlite3_pcache Methods **********************************************/ /* ** Implementation of the sqlite3_pcache.xInit method. */ static int pcache1Init(void *NotUsed){ UNUSED_PARAMETER(NotUsed); assert( pcache1.isInit==0 ); memset(&pcache1, 0, sizeof(pcache1)); /* ** The pcache1.separateCache variable is true if each PCache has its own ** private PGroup (mode-1). pcache1.separateCache is false if the single ** PGroup in pcache1.grp is used for all page caches (mode-2). ** ** * Always use a unified cache (mode-2) if ENABLE_MEMORY_MANAGEMENT ** ** * Use a unified cache in single-threaded applications that have ** configured a start-time buffer for use as page-cache memory using ** sqlite3_config(SQLITE_CONFIG_PAGECACHE, pBuf, sz, N) with non-NULL ** pBuf argument. ** ** * Otherwise use separate caches (mode-1) */ #if defined(SQLITE_ENABLE_MEMORY_MANAGEMENT) pcache1.separateCache = 0; #elif SQLITE_THREADSAFE pcache1.separateCache = sqlite3GlobalConfig.pPage==0 || sqlite3GlobalConfig.bCoreMutex>0; #else pcache1.separateCache = sqlite3GlobalConfig.pPage==0; #endif #if SQLITE_THREADSAFE if( sqlite3GlobalConfig.bCoreMutex ){ pcache1.grp.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_LRU); pcache1.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PMEM); } #endif if( pcache1.separateCache && sqlite3GlobalConfig.nPage!=0 && sqlite3GlobalConfig.pPage==0 ){ pcache1.nInitPage = sqlite3GlobalConfig.nPage; }else{ pcache1.nInitPage = 0; } pcache1.grp.mxPinned = 10; pcache1.isInit = 1; return SQLITE_OK; } /* ** Implementation of the sqlite3_pcache.xShutdown method. ** Note that the static mutex allocated in xInit does ** not need to be freed. */ static void pcache1Shutdown(void *NotUsed){ UNUSED_PARAMETER(NotUsed); assert( pcache1.isInit!=0 ); memset(&pcache1, 0, sizeof(pcache1)); } /* forward declaration */ static void pcache1Destroy(sqlite3_pcache *p); /* ** Implementation of the sqlite3_pcache.xCreate method. ** ** Allocate a new cache. */ static sqlite3_pcache *pcache1Create(int szPage, int szExtra, int bPurgeable){ PCache1 *pCache; /* The newly created page cache */ PGroup *pGroup; /* The group the new page cache will belong to */ int sz; /* Bytes of memory required to allocate the new cache */ assert( (szPage & (szPage-1))==0 && szPage>=512 && szPage<=65536 ); assert( szExtra < 300 ); sz = sizeof(PCache1) + sizeof(PGroup)*pcache1.separateCache; pCache = (PCache1 *)sqlite3MallocZero(sz); if( pCache ){ if( pcache1.separateCache ){ pGroup = (PGroup*)&pCache[1]; pGroup->mxPinned = 10; }else{ pGroup = &pcache1.grp; } if( pGroup->lru.isAnchor==0 ){ pGroup->lru.isAnchor = 1; pGroup->lru.pLruPrev = pGroup->lru.pLruNext = &pGroup->lru; } pCache->pGroup = pGroup; pCache->szPage = szPage; pCache->szExtra = szExtra; pCache->szAlloc = szPage + szExtra + ROUND8(sizeof(PgHdr1)); pCache->bPurgeable = (bPurgeable ? 1 : 0); pcache1EnterMutex(pGroup); pcache1ResizeHash(pCache); if( bPurgeable ){ pCache->nMin = 10; pGroup->nMinPage += pCache->nMin; pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage; pCache->pnPurgeable = &pGroup->nPurgeable; }else{ static unsigned int dummyCurrentPage; pCache->pnPurgeable = &dummyCurrentPage; } pcache1LeaveMutex(pGroup); if( pCache->nHash==0 ){ pcache1Destroy((sqlite3_pcache*)pCache); pCache = 0; } } return (sqlite3_pcache *)pCache; } /* ** Implementation of the sqlite3_pcache.xCachesize method. ** ** Configure the cache_size limit for a cache. */ static void pcache1Cachesize(sqlite3_pcache *p, int nMax){ PCache1 *pCache = (PCache1 *)p; if( pCache->bPurgeable ){ PGroup *pGroup = pCache->pGroup; pcache1EnterMutex(pGroup); pGroup->nMaxPage += (nMax - pCache->nMax); pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage; pCache->nMax = nMax; pCache->n90pct = pCache->nMax*9/10; pcache1EnforceMaxPage(pCache); pcache1LeaveMutex(pGroup); } } /* ** Implementation of the sqlite3_pcache.xShrink method. ** ** Free up as much memory as possible. */ static void pcache1Shrink(sqlite3_pcache *p){ PCache1 *pCache = (PCache1*)p; if( pCache->bPurgeable ){ PGroup *pGroup = pCache->pGroup; int savedMaxPage; pcache1EnterMutex(pGroup); savedMaxPage = pGroup->nMaxPage; pGroup->nMaxPage = 0; pcache1EnforceMaxPage(pCache); pGroup->nMaxPage = savedMaxPage; pcache1LeaveMutex(pGroup); } } /* ** Implementation of the sqlite3_pcache.xPagecount method. */ static int pcache1Pagecount(sqlite3_pcache *p){ int n; PCache1 *pCache = (PCache1*)p; pcache1EnterMutex(pCache->pGroup); n = pCache->nPage; pcache1LeaveMutex(pCache->pGroup); return n; } /* ** Implement steps 3, 4, and 5 of the pcache1Fetch() algorithm described ** in the header of the pcache1Fetch() procedure. ** ** This steps are broken out into a separate procedure because they are ** usually not needed, and by avoiding the stack initialization required ** for these steps, the main pcache1Fetch() procedure can run faster. */ static SQLITE_NOINLINE PgHdr1 *pcache1FetchStage2( PCache1 *pCache, unsigned int iKey, int createFlag ){ unsigned int nPinned; PGroup *pGroup = pCache->pGroup; PgHdr1 *pPage = 0; /* Step 3: Abort if createFlag is 1 but the cache is nearly full */ assert( pCache->nPage >= pCache->nRecyclable ); nPinned = pCache->nPage - pCache->nRecyclable; assert( pGroup->mxPinned == pGroup->nMaxPage + 10 - pGroup->nMinPage ); assert( pCache->n90pct == pCache->nMax*9/10 ); if( createFlag==1 && ( nPinned>=pGroup->mxPinned || nPinned>=pCache->n90pct || (pcache1UnderMemoryPressure(pCache) && pCache->nRecyclable<nPinned) )){ return 0; } if( pCache->nPage>=pCache->nHash ) pcache1ResizeHash(pCache); assert( pCache->nHash>0 && pCache->apHash ); /* Step 4. Try to recycle a page. */ if( pCache->bPurgeable && !pGroup->lru.pLruPrev->isAnchor && ((pCache->nPage+1>=pCache->nMax) || pcache1UnderMemoryPressure(pCache)) ){ PCache1 *pOther; pPage = pGroup->lru.pLruPrev; assert( PAGE_IS_UNPINNED(pPage) ); pcache1RemoveFromHash(pPage, 0); pcache1PinPage(pPage); pOther = pPage->pCache; if( pOther->szAlloc != pCache->szAlloc ){ pcache1FreePage(pPage); pPage = 0; }else{ pGroup->nPurgeable -= (pOther->bPurgeable - pCache->bPurgeable); } } /* Step 5. If a usable page buffer has still not been found, ** attempt to allocate a new one. */ if( !pPage ){ pPage = pcache1AllocPage(pCache, createFlag==1); } if( pPage ){ unsigned int h = iKey % pCache->nHash; pCache->nPage++; pPage->iKey = iKey; pPage->pNext = pCache->apHash[h]; pPage->pCache = pCache; pPage->pLruPrev = 0; pPage->pLruNext = 0; *(void **)pPage->page.pExtra = 0; pCache->apHash[h] = pPage; if( iKey>pCache->iMaxKey ){ pCache->iMaxKey = iKey; } } return pPage; } /* ** Implementation of the sqlite3_pcache.xFetch method. ** ** Fetch a page by key value. ** ** Whether or not a new page may be allocated by this function depends on ** the value of the createFlag argument. 0 means do not allocate a new ** page. 1 means allocate a new page if space is easily available. 2 ** means to try really hard to allocate a new page. ** ** For a non-purgeable cache (a cache used as the storage for an in-memory ** database) there is really no difference between createFlag 1 and 2. So ** the calling function (pcache.c) will never have a createFlag of 1 on ** a non-purgeable cache. ** ** There are three different approaches to obtaining space for a page, ** depending on the value of parameter createFlag (which may be 0, 1 or 2). ** ** 1. Regardless of the value of createFlag, the cache is searched for a ** copy of the requested page. If one is found, it is returned. ** ** 2. If createFlag==0 and the page is not already in the cache, NULL is ** returned. ** ** 3. If createFlag is 1, and the page is not already in the cache, then ** return NULL (do not allocate a new page) if any of the following ** conditions are true: ** ** (a) the number of pages pinned by the cache is greater than ** PCache1.nMax, or ** ** (b) the number of pages pinned by the cache is greater than ** the sum of nMax for all purgeable caches, less the sum of ** nMin for all other purgeable caches, or ** ** 4. If none of the first three conditions apply and the cache is marked ** as purgeable, and if one of the following is true: ** ** (a) The number of pages allocated for the cache is already ** PCache1.nMax, or ** ** (b) The number of pages allocated for all purgeable caches is ** already equal to or greater than the sum of nMax for all ** purgeable caches, ** ** (c) The system is under memory pressure and wants to avoid ** unnecessary pages cache entry allocations ** ** then attempt to recycle a page from the LRU list. If it is the right ** size, return the recycled buffer. Otherwise, free the buffer and ** proceed to step 5. ** ** 5. Otherwise, allocate and return a new page buffer. ** ** There are two versions of this routine. pcache1FetchWithMutex() is ** the general case. pcache1FetchNoMutex() is a faster implementation for ** the common case where pGroup->mutex is NULL. The pcache1Fetch() wrapper ** invokes the appropriate routine. */ static PgHdr1 *pcache1FetchNoMutex( sqlite3_pcache *p, unsigned int iKey, int createFlag ){ PCache1 *pCache = (PCache1 *)p; PgHdr1 *pPage = 0; /* Step 1: Search the hash table for an existing entry. */ pPage = pCache->apHash[iKey % pCache->nHash]; while( pPage && pPage->iKey!=iKey ){ pPage = pPage->pNext; } /* Step 2: If the page was found in the hash table, then return it. ** If the page was not in the hash table and createFlag is 0, abort. ** Otherwise (page not in hash and createFlag!=0) continue with ** subsequent steps to try to create the page. */ if( pPage ){ if( PAGE_IS_UNPINNED(pPage) ){ return pcache1PinPage(pPage); }else{ |
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