000001 /*
000002 ** 2008 August 05
000003 **
000004 ** The author disclaims copyright to this source code. In place of
000005 ** a legal notice, here is a blessing:
000006 **
000007 ** May you do good and not evil.
000008 ** May you find forgiveness for yourself and forgive others.
000009 ** May you share freely, never taking more than you give.
000010 **
000011 *************************************************************************
000012 ** This file implements that page cache.
000013 */
000014 #include "sqliteInt.h"
000015
000016 /*
000017 ** A complete page cache is an instance of this structure. Every
000018 ** entry in the cache holds a single page of the database file. The
000019 ** btree layer only operates on the cached copy of the database pages.
000020 **
000021 ** A page cache entry is "clean" if it exactly matches what is currently
000022 ** on disk. A page is "dirty" if it has been modified and needs to be
000023 ** persisted to disk.
000024 **
000025 ** pDirty, pDirtyTail, pSynced:
000026 ** All dirty pages are linked into the doubly linked list using
000027 ** PgHdr.pDirtyNext and pDirtyPrev. The list is maintained in LRU order
000028 ** such that p was added to the list more recently than p->pDirtyNext.
000029 ** PCache.pDirty points to the first (newest) element in the list and
000030 ** pDirtyTail to the last (oldest).
000031 **
000032 ** The PCache.pSynced variable is used to optimize searching for a dirty
000033 ** page to eject from the cache mid-transaction. It is better to eject
000034 ** a page that does not require a journal sync than one that does.
000035 ** Therefore, pSynced is maintained so that it *almost* always points
000036 ** to either the oldest page in the pDirty/pDirtyTail list that has a
000037 ** clear PGHDR_NEED_SYNC flag or to a page that is older than this one
000038 ** (so that the right page to eject can be found by following pDirtyPrev
000039 ** pointers).
000040 */
000041 struct PCache {
000042 PgHdr *pDirty, *pDirtyTail; /* List of dirty pages in LRU order */
000043 PgHdr *pSynced; /* Last synced page in dirty page list */
000044 int nRefSum; /* Sum of ref counts over all pages */
000045 int szCache; /* Configured cache size */
000046 int szSpill; /* Size before spilling occurs */
000047 int szPage; /* Size of every page in this cache */
000048 int szExtra; /* Size of extra space for each page */
000049 u8 bPurgeable; /* True if pages are on backing store */
000050 u8 eCreate; /* eCreate value for for xFetch() */
000051 int (*xStress)(void*,PgHdr*); /* Call to try make a page clean */
000052 void *pStress; /* Argument to xStress */
000053 sqlite3_pcache *pCache; /* Pluggable cache module */
000054 };
000055
000056 /********************************** Test and Debug Logic **********************/
000057 /*
000058 ** Debug tracing macros. Enable by by changing the "0" to "1" and
000059 ** recompiling.
000060 **
000061 ** When sqlite3PcacheTrace is 1, single line trace messages are issued.
000062 ** When sqlite3PcacheTrace is 2, a dump of the pcache showing all cache entries
000063 ** is displayed for many operations, resulting in a lot of output.
000064 */
000065 #if defined(SQLITE_DEBUG) && 0
000066 int sqlite3PcacheTrace = 2; /* 0: off 1: simple 2: cache dumps */
000067 int sqlite3PcacheMxDump = 9999; /* Max cache entries for pcacheDump() */
000068 # define pcacheTrace(X) if(sqlite3PcacheTrace){sqlite3DebugPrintf X;}
000069 void pcacheDump(PCache *pCache){
000070 int N;
000071 int i, j;
000072 sqlite3_pcache_page *pLower;
000073 PgHdr *pPg;
000074 unsigned char *a;
000075
000076 if( sqlite3PcacheTrace<2 ) return;
000077 if( pCache->pCache==0 ) return;
000078 N = sqlite3PcachePagecount(pCache);
000079 if( N>sqlite3PcacheMxDump ) N = sqlite3PcacheMxDump;
000080 for(i=1; i<=N; i++){
000081 pLower = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, i, 0);
000082 if( pLower==0 ) continue;
000083 pPg = (PgHdr*)pLower->pExtra;
000084 printf("%3d: nRef %2d flgs %02x data ", i, pPg->nRef, pPg->flags);
000085 a = (unsigned char *)pLower->pBuf;
000086 for(j=0; j<12; j++) printf("%02x", a[j]);
000087 printf("\n");
000088 if( pPg->pPage==0 ){
000089 sqlite3GlobalConfig.pcache2.xUnpin(pCache->pCache, pLower, 0);
000090 }
000091 }
000092 }
000093 #else
000094 # define pcacheTrace(X)
000095 # define pcacheDump(X)
000096 #endif
000097
000098 /*
000099 ** Check invariants on a PgHdr entry. Return true if everything is OK.
000100 ** Return false if any invariant is violated.
000101 **
000102 ** This routine is for use inside of assert() statements only. For
000103 ** example:
000104 **
000105 ** assert( sqlite3PcachePageSanity(pPg) );
000106 */
000107 #ifdef SQLITE_DEBUG
000108 int sqlite3PcachePageSanity(PgHdr *pPg){
000109 PCache *pCache;
000110 assert( pPg!=0 );
000111 assert( pPg->pgno>0 || pPg->pPager==0 ); /* Page number is 1 or more */
000112 pCache = pPg->pCache;
000113 assert( pCache!=0 ); /* Every page has an associated PCache */
000114 if( pPg->flags & PGHDR_CLEAN ){
000115 assert( (pPg->flags & PGHDR_DIRTY)==0 );/* Cannot be both CLEAN and DIRTY */
000116 assert( pCache->pDirty!=pPg ); /* CLEAN pages not on dirty list */
000117 assert( pCache->pDirtyTail!=pPg );
000118 }
000119 /* WRITEABLE pages must also be DIRTY */
000120 if( pPg->flags & PGHDR_WRITEABLE ){
000121 assert( pPg->flags & PGHDR_DIRTY ); /* WRITEABLE implies DIRTY */
000122 }
000123 /* NEED_SYNC can be set independently of WRITEABLE. This can happen,
000124 ** for example, when using the sqlite3PagerDontWrite() optimization:
000125 ** (1) Page X is journalled, and gets WRITEABLE and NEED_SEEK.
000126 ** (2) Page X moved to freelist, WRITEABLE is cleared
000127 ** (3) Page X reused, WRITEABLE is set again
000128 ** If NEED_SYNC had been cleared in step 2, then it would not be reset
000129 ** in step 3, and page might be written into the database without first
000130 ** syncing the rollback journal, which might cause corruption on a power
000131 ** loss.
000132 **
000133 ** Another example is when the database page size is smaller than the
000134 ** disk sector size. When any page of a sector is journalled, all pages
000135 ** in that sector are marked NEED_SYNC even if they are still CLEAN, just
000136 ** in case they are later modified, since all pages in the same sector
000137 ** must be journalled and synced before any of those pages can be safely
000138 ** written.
000139 */
000140 return 1;
000141 }
000142 #endif /* SQLITE_DEBUG */
000143
000144
000145 /********************************** Linked List Management ********************/
000146
000147 /* Allowed values for second argument to pcacheManageDirtyList() */
000148 #define PCACHE_DIRTYLIST_REMOVE 1 /* Remove pPage from dirty list */
000149 #define PCACHE_DIRTYLIST_ADD 2 /* Add pPage to the dirty list */
000150 #define PCACHE_DIRTYLIST_FRONT 3 /* Move pPage to the front of the list */
000151
000152 /*
000153 ** Manage pPage's participation on the dirty list. Bits of the addRemove
000154 ** argument determines what operation to do. The 0x01 bit means first
000155 ** remove pPage from the dirty list. The 0x02 means add pPage back to
000156 ** the dirty list. Doing both moves pPage to the front of the dirty list.
000157 */
000158 static void pcacheManageDirtyList(PgHdr *pPage, u8 addRemove){
000159 PCache *p = pPage->pCache;
000160
000161 pcacheTrace(("%p.DIRTYLIST.%s %d\n", p,
000162 addRemove==1 ? "REMOVE" : addRemove==2 ? "ADD" : "FRONT",
000163 pPage->pgno));
000164 if( addRemove & PCACHE_DIRTYLIST_REMOVE ){
000165 assert( pPage->pDirtyNext || pPage==p->pDirtyTail );
000166 assert( pPage->pDirtyPrev || pPage==p->pDirty );
000167
000168 /* Update the PCache1.pSynced variable if necessary. */
000169 if( p->pSynced==pPage ){
000170 p->pSynced = pPage->pDirtyPrev;
000171 }
000172
000173 if( pPage->pDirtyNext ){
000174 pPage->pDirtyNext->pDirtyPrev = pPage->pDirtyPrev;
000175 }else{
000176 assert( pPage==p->pDirtyTail );
000177 p->pDirtyTail = pPage->pDirtyPrev;
000178 }
000179 if( pPage->pDirtyPrev ){
000180 pPage->pDirtyPrev->pDirtyNext = pPage->pDirtyNext;
000181 }else{
000182 /* If there are now no dirty pages in the cache, set eCreate to 2.
000183 ** This is an optimization that allows sqlite3PcacheFetch() to skip
000184 ** searching for a dirty page to eject from the cache when it might
000185 ** otherwise have to. */
000186 assert( pPage==p->pDirty );
000187 p->pDirty = pPage->pDirtyNext;
000188 assert( p->bPurgeable || p->eCreate==2 );
000189 if( p->pDirty==0 ){ /*OPTIMIZATION-IF-TRUE*/
000190 assert( p->bPurgeable==0 || p->eCreate==1 );
000191 p->eCreate = 2;
000192 }
000193 }
000194 }
000195 if( addRemove & PCACHE_DIRTYLIST_ADD ){
000196 pPage->pDirtyPrev = 0;
000197 pPage->pDirtyNext = p->pDirty;
000198 if( pPage->pDirtyNext ){
000199 assert( pPage->pDirtyNext->pDirtyPrev==0 );
000200 pPage->pDirtyNext->pDirtyPrev = pPage;
000201 }else{
000202 p->pDirtyTail = pPage;
000203 if( p->bPurgeable ){
000204 assert( p->eCreate==2 );
000205 p->eCreate = 1;
000206 }
000207 }
000208 p->pDirty = pPage;
000209
000210 /* If pSynced is NULL and this page has a clear NEED_SYNC flag, set
000211 ** pSynced to point to it. Checking the NEED_SYNC flag is an
000212 ** optimization, as if pSynced points to a page with the NEED_SYNC
000213 ** flag set sqlite3PcacheFetchStress() searches through all newer
000214 ** entries of the dirty-list for a page with NEED_SYNC clear anyway. */
000215 if( !p->pSynced
000216 && 0==(pPage->flags&PGHDR_NEED_SYNC) /*OPTIMIZATION-IF-FALSE*/
000217 ){
000218 p->pSynced = pPage;
000219 }
000220 }
000221 pcacheDump(p);
000222 }
000223
000224 /*
000225 ** Wrapper around the pluggable caches xUnpin method. If the cache is
000226 ** being used for an in-memory database, this function is a no-op.
000227 */
000228 static void pcacheUnpin(PgHdr *p){
000229 if( p->pCache->bPurgeable ){
000230 pcacheTrace(("%p.UNPIN %d\n", p->pCache, p->pgno));
000231 sqlite3GlobalConfig.pcache2.xUnpin(p->pCache->pCache, p->pPage, 0);
000232 pcacheDump(p->pCache);
000233 }
000234 }
000235
000236 /*
000237 ** Compute the number of pages of cache requested. p->szCache is the
000238 ** cache size requested by the "PRAGMA cache_size" statement.
000239 */
000240 static int numberOfCachePages(PCache *p){
000241 if( p->szCache>=0 ){
000242 /* IMPLEMENTATION-OF: R-42059-47211 If the argument N is positive then the
000243 ** suggested cache size is set to N. */
000244 return p->szCache;
000245 }else{
000246 /* IMPLEMANTATION-OF: R-59858-46238 If the argument N is negative, then the
000247 ** number of cache pages is adjusted to be a number of pages that would
000248 ** use approximately abs(N*1024) bytes of memory based on the current
000249 ** page size. */
000250 return (int)((-1024*(i64)p->szCache)/(p->szPage+p->szExtra));
000251 }
000252 }
000253
000254 /*************************************************** General Interfaces ******
000255 **
000256 ** Initialize and shutdown the page cache subsystem. Neither of these
000257 ** functions are threadsafe.
000258 */
000259 int sqlite3PcacheInitialize(void){
000260 if( sqlite3GlobalConfig.pcache2.xInit==0 ){
000261 /* IMPLEMENTATION-OF: R-26801-64137 If the xInit() method is NULL, then the
000262 ** built-in default page cache is used instead of the application defined
000263 ** page cache. */
000264 sqlite3PCacheSetDefault();
000265 assert( sqlite3GlobalConfig.pcache2.xInit!=0 );
000266 }
000267 return sqlite3GlobalConfig.pcache2.xInit(sqlite3GlobalConfig.pcache2.pArg);
000268 }
000269 void sqlite3PcacheShutdown(void){
000270 if( sqlite3GlobalConfig.pcache2.xShutdown ){
000271 /* IMPLEMENTATION-OF: R-26000-56589 The xShutdown() method may be NULL. */
000272 sqlite3GlobalConfig.pcache2.xShutdown(sqlite3GlobalConfig.pcache2.pArg);
000273 }
000274 }
000275
000276 /*
000277 ** Return the size in bytes of a PCache object.
000278 */
000279 int sqlite3PcacheSize(void){ return sizeof(PCache); }
000280
000281 /*
000282 ** Create a new PCache object. Storage space to hold the object
000283 ** has already been allocated and is passed in as the p pointer.
000284 ** The caller discovers how much space needs to be allocated by
000285 ** calling sqlite3PcacheSize().
000286 **
000287 ** szExtra is some extra space allocated for each page. The first
000288 ** 8 bytes of the extra space will be zeroed as the page is allocated,
000289 ** but remaining content will be uninitialized. Though it is opaque
000290 ** to this module, the extra space really ends up being the MemPage
000291 ** structure in the pager.
000292 */
000293 int sqlite3PcacheOpen(
000294 int szPage, /* Size of every page */
000295 int szExtra, /* Extra space associated with each page */
000296 int bPurgeable, /* True if pages are on backing store */
000297 int (*xStress)(void*,PgHdr*),/* Call to try to make pages clean */
000298 void *pStress, /* Argument to xStress */
000299 PCache *p /* Preallocated space for the PCache */
000300 ){
000301 memset(p, 0, sizeof(PCache));
000302 p->szPage = 1;
000303 p->szExtra = szExtra;
000304 assert( szExtra>=8 ); /* First 8 bytes will be zeroed */
000305 p->bPurgeable = bPurgeable;
000306 p->eCreate = 2;
000307 p->xStress = xStress;
000308 p->pStress = pStress;
000309 p->szCache = 100;
000310 p->szSpill = 1;
000311 pcacheTrace(("%p.OPEN szPage %d bPurgeable %d\n",p,szPage,bPurgeable));
000312 return sqlite3PcacheSetPageSize(p, szPage);
000313 }
000314
000315 /*
000316 ** Change the page size for PCache object. The caller must ensure that there
000317 ** are no outstanding page references when this function is called.
000318 */
000319 int sqlite3PcacheSetPageSize(PCache *pCache, int szPage){
000320 assert( pCache->nRefSum==0 && pCache->pDirty==0 );
000321 if( pCache->szPage ){
000322 sqlite3_pcache *pNew;
000323 pNew = sqlite3GlobalConfig.pcache2.xCreate(
000324 szPage, pCache->szExtra + ROUND8(sizeof(PgHdr)),
000325 pCache->bPurgeable
000326 );
000327 if( pNew==0 ) return SQLITE_NOMEM_BKPT;
000328 sqlite3GlobalConfig.pcache2.xCachesize(pNew, numberOfCachePages(pCache));
000329 if( pCache->pCache ){
000330 sqlite3GlobalConfig.pcache2.xDestroy(pCache->pCache);
000331 }
000332 pCache->pCache = pNew;
000333 pCache->szPage = szPage;
000334 pcacheTrace(("%p.PAGESIZE %d\n",pCache,szPage));
000335 }
000336 return SQLITE_OK;
000337 }
000338
000339 /*
000340 ** Try to obtain a page from the cache.
000341 **
000342 ** This routine returns a pointer to an sqlite3_pcache_page object if
000343 ** such an object is already in cache, or if a new one is created.
000344 ** This routine returns a NULL pointer if the object was not in cache
000345 ** and could not be created.
000346 **
000347 ** The createFlags should be 0 to check for existing pages and should
000348 ** be 3 (not 1, but 3) to try to create a new page.
000349 **
000350 ** If the createFlag is 0, then NULL is always returned if the page
000351 ** is not already in the cache. If createFlag is 1, then a new page
000352 ** is created only if that can be done without spilling dirty pages
000353 ** and without exceeding the cache size limit.
000354 **
000355 ** The caller needs to invoke sqlite3PcacheFetchFinish() to properly
000356 ** initialize the sqlite3_pcache_page object and convert it into a
000357 ** PgHdr object. The sqlite3PcacheFetch() and sqlite3PcacheFetchFinish()
000358 ** routines are split this way for performance reasons. When separated
000359 ** they can both (usually) operate without having to push values to
000360 ** the stack on entry and pop them back off on exit, which saves a
000361 ** lot of pushing and popping.
000362 */
000363 sqlite3_pcache_page *sqlite3PcacheFetch(
000364 PCache *pCache, /* Obtain the page from this cache */
000365 Pgno pgno, /* Page number to obtain */
000366 int createFlag /* If true, create page if it does not exist already */
000367 ){
000368 int eCreate;
000369 sqlite3_pcache_page *pRes;
000370
000371 assert( pCache!=0 );
000372 assert( pCache->pCache!=0 );
000373 assert( createFlag==3 || createFlag==0 );
000374 assert( pCache->eCreate==((pCache->bPurgeable && pCache->pDirty) ? 1 : 2) );
000375
000376 /* eCreate defines what to do if the page does not exist.
000377 ** 0 Do not allocate a new page. (createFlag==0)
000378 ** 1 Allocate a new page if doing so is inexpensive.
000379 ** (createFlag==1 AND bPurgeable AND pDirty)
000380 ** 2 Allocate a new page even it doing so is difficult.
000381 ** (createFlag==1 AND !(bPurgeable AND pDirty)
000382 */
000383 eCreate = createFlag & pCache->eCreate;
000384 assert( eCreate==0 || eCreate==1 || eCreate==2 );
000385 assert( createFlag==0 || pCache->eCreate==eCreate );
000386 assert( createFlag==0 || eCreate==1+(!pCache->bPurgeable||!pCache->pDirty) );
000387 pRes = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, eCreate);
000388 pcacheTrace(("%p.FETCH %d%s (result: %p)\n",pCache,pgno,
000389 createFlag?" create":"",pRes));
000390 return pRes;
000391 }
000392
000393 /*
000394 ** If the sqlite3PcacheFetch() routine is unable to allocate a new
000395 ** page because no clean pages are available for reuse and the cache
000396 ** size limit has been reached, then this routine can be invoked to
000397 ** try harder to allocate a page. This routine might invoke the stress
000398 ** callback to spill dirty pages to the journal. It will then try to
000399 ** allocate the new page and will only fail to allocate a new page on
000400 ** an OOM error.
000401 **
000402 ** This routine should be invoked only after sqlite3PcacheFetch() fails.
000403 */
000404 int sqlite3PcacheFetchStress(
000405 PCache *pCache, /* Obtain the page from this cache */
000406 Pgno pgno, /* Page number to obtain */
000407 sqlite3_pcache_page **ppPage /* Write result here */
000408 ){
000409 PgHdr *pPg;
000410 if( pCache->eCreate==2 ) return 0;
000411
000412 if( sqlite3PcachePagecount(pCache)>pCache->szSpill ){
000413 /* Find a dirty page to write-out and recycle. First try to find a
000414 ** page that does not require a journal-sync (one with PGHDR_NEED_SYNC
000415 ** cleared), but if that is not possible settle for any other
000416 ** unreferenced dirty page.
000417 **
000418 ** If the LRU page in the dirty list that has a clear PGHDR_NEED_SYNC
000419 ** flag is currently referenced, then the following may leave pSynced
000420 ** set incorrectly (pointing to other than the LRU page with NEED_SYNC
000421 ** cleared). This is Ok, as pSynced is just an optimization. */
000422 for(pPg=pCache->pSynced;
000423 pPg && (pPg->nRef || (pPg->flags&PGHDR_NEED_SYNC));
000424 pPg=pPg->pDirtyPrev
000425 );
000426 pCache->pSynced = pPg;
000427 if( !pPg ){
000428 for(pPg=pCache->pDirtyTail; pPg && pPg->nRef; pPg=pPg->pDirtyPrev);
000429 }
000430 if( pPg ){
000431 int rc;
000432 #ifdef SQLITE_LOG_CACHE_SPILL
000433 sqlite3_log(SQLITE_FULL,
000434 "spill page %d making room for %d - cache used: %d/%d",
000435 pPg->pgno, pgno,
000436 sqlite3GlobalConfig.pcache2.xPagecount(pCache->pCache),
000437 numberOfCachePages(pCache));
000438 #endif
000439 pcacheTrace(("%p.SPILL %d\n",pCache,pPg->pgno));
000440 rc = pCache->xStress(pCache->pStress, pPg);
000441 pcacheDump(pCache);
000442 if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
000443 return rc;
000444 }
000445 }
000446 }
000447 *ppPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, 2);
000448 return *ppPage==0 ? SQLITE_NOMEM_BKPT : SQLITE_OK;
000449 }
000450
000451 /*
000452 ** This is a helper routine for sqlite3PcacheFetchFinish()
000453 **
000454 ** In the uncommon case where the page being fetched has not been
000455 ** initialized, this routine is invoked to do the initialization.
000456 ** This routine is broken out into a separate function since it
000457 ** requires extra stack manipulation that can be avoided in the common
000458 ** case.
000459 */
000460 static SQLITE_NOINLINE PgHdr *pcacheFetchFinishWithInit(
000461 PCache *pCache, /* Obtain the page from this cache */
000462 Pgno pgno, /* Page number obtained */
000463 sqlite3_pcache_page *pPage /* Page obtained by prior PcacheFetch() call */
000464 ){
000465 PgHdr *pPgHdr;
000466 assert( pPage!=0 );
000467 pPgHdr = (PgHdr*)pPage->pExtra;
000468 assert( pPgHdr->pPage==0 );
000469 memset(&pPgHdr->pDirty, 0, sizeof(PgHdr) - offsetof(PgHdr,pDirty));
000470 pPgHdr->pPage = pPage;
000471 pPgHdr->pData = pPage->pBuf;
000472 pPgHdr->pExtra = (void *)&pPgHdr[1];
000473 memset(pPgHdr->pExtra, 0, 8);
000474 pPgHdr->pCache = pCache;
000475 pPgHdr->pgno = pgno;
000476 pPgHdr->flags = PGHDR_CLEAN;
000477 return sqlite3PcacheFetchFinish(pCache,pgno,pPage);
000478 }
000479
000480 /*
000481 ** This routine converts the sqlite3_pcache_page object returned by
000482 ** sqlite3PcacheFetch() into an initialized PgHdr object. This routine
000483 ** must be called after sqlite3PcacheFetch() in order to get a usable
000484 ** result.
000485 */
000486 PgHdr *sqlite3PcacheFetchFinish(
000487 PCache *pCache, /* Obtain the page from this cache */
000488 Pgno pgno, /* Page number obtained */
000489 sqlite3_pcache_page *pPage /* Page obtained by prior PcacheFetch() call */
000490 ){
000491 PgHdr *pPgHdr;
000492
000493 assert( pPage!=0 );
000494 pPgHdr = (PgHdr *)pPage->pExtra;
000495
000496 if( !pPgHdr->pPage ){
000497 return pcacheFetchFinishWithInit(pCache, pgno, pPage);
000498 }
000499 pCache->nRefSum++;
000500 pPgHdr->nRef++;
000501 assert( sqlite3PcachePageSanity(pPgHdr) );
000502 return pPgHdr;
000503 }
000504
000505 /*
000506 ** Decrement the reference count on a page. If the page is clean and the
000507 ** reference count drops to 0, then it is made eligible for recycling.
000508 */
000509 void SQLITE_NOINLINE sqlite3PcacheRelease(PgHdr *p){
000510 assert( p->nRef>0 );
000511 p->pCache->nRefSum--;
000512 if( (--p->nRef)==0 ){
000513 if( p->flags&PGHDR_CLEAN ){
000514 pcacheUnpin(p);
000515 }else{
000516 pcacheManageDirtyList(p, PCACHE_DIRTYLIST_FRONT);
000517 }
000518 }
000519 }
000520
000521 /*
000522 ** Increase the reference count of a supplied page by 1.
000523 */
000524 void sqlite3PcacheRef(PgHdr *p){
000525 assert(p->nRef>0);
000526 assert( sqlite3PcachePageSanity(p) );
000527 p->nRef++;
000528 p->pCache->nRefSum++;
000529 }
000530
000531 /*
000532 ** Drop a page from the cache. There must be exactly one reference to the
000533 ** page. This function deletes that reference, so after it returns the
000534 ** page pointed to by p is invalid.
000535 */
000536 void sqlite3PcacheDrop(PgHdr *p){
000537 assert( p->nRef==1 );
000538 assert( sqlite3PcachePageSanity(p) );
000539 if( p->flags&PGHDR_DIRTY ){
000540 pcacheManageDirtyList(p, PCACHE_DIRTYLIST_REMOVE);
000541 }
000542 p->pCache->nRefSum--;
000543 sqlite3GlobalConfig.pcache2.xUnpin(p->pCache->pCache, p->pPage, 1);
000544 }
000545
000546 /*
000547 ** Make sure the page is marked as dirty. If it isn't dirty already,
000548 ** make it so.
000549 */
000550 void sqlite3PcacheMakeDirty(PgHdr *p){
000551 assert( p->nRef>0 );
000552 assert( sqlite3PcachePageSanity(p) );
000553 if( p->flags & (PGHDR_CLEAN|PGHDR_DONT_WRITE) ){ /*OPTIMIZATION-IF-FALSE*/
000554 p->flags &= ~PGHDR_DONT_WRITE;
000555 if( p->flags & PGHDR_CLEAN ){
000556 p->flags ^= (PGHDR_DIRTY|PGHDR_CLEAN);
000557 pcacheTrace(("%p.DIRTY %d\n",p->pCache,p->pgno));
000558 assert( (p->flags & (PGHDR_DIRTY|PGHDR_CLEAN))==PGHDR_DIRTY );
000559 pcacheManageDirtyList(p, PCACHE_DIRTYLIST_ADD);
000560 }
000561 assert( sqlite3PcachePageSanity(p) );
000562 }
000563 }
000564
000565 /*
000566 ** Make sure the page is marked as clean. If it isn't clean already,
000567 ** make it so.
000568 */
000569 void sqlite3PcacheMakeClean(PgHdr *p){
000570 assert( sqlite3PcachePageSanity(p) );
000571 assert( (p->flags & PGHDR_DIRTY)!=0 );
000572 assert( (p->flags & PGHDR_CLEAN)==0 );
000573 pcacheManageDirtyList(p, PCACHE_DIRTYLIST_REMOVE);
000574 p->flags &= ~(PGHDR_DIRTY|PGHDR_NEED_SYNC|PGHDR_WRITEABLE);
000575 p->flags |= PGHDR_CLEAN;
000576 pcacheTrace(("%p.CLEAN %d\n",p->pCache,p->pgno));
000577 assert( sqlite3PcachePageSanity(p) );
000578 if( p->nRef==0 ){
000579 pcacheUnpin(p);
000580 }
000581 }
000582
000583 /*
000584 ** Make every page in the cache clean.
000585 */
000586 void sqlite3PcacheCleanAll(PCache *pCache){
000587 PgHdr *p;
000588 pcacheTrace(("%p.CLEAN-ALL\n",pCache));
000589 while( (p = pCache->pDirty)!=0 ){
000590 sqlite3PcacheMakeClean(p);
000591 }
000592 }
000593
000594 /*
000595 ** Clear the PGHDR_NEED_SYNC and PGHDR_WRITEABLE flag from all dirty pages.
000596 */
000597 void sqlite3PcacheClearWritable(PCache *pCache){
000598 PgHdr *p;
000599 pcacheTrace(("%p.CLEAR-WRITEABLE\n",pCache));
000600 for(p=pCache->pDirty; p; p=p->pDirtyNext){
000601 p->flags &= ~(PGHDR_NEED_SYNC|PGHDR_WRITEABLE);
000602 }
000603 pCache->pSynced = pCache->pDirtyTail;
000604 }
000605
000606 /*
000607 ** Clear the PGHDR_NEED_SYNC flag from all dirty pages.
000608 */
000609 void sqlite3PcacheClearSyncFlags(PCache *pCache){
000610 PgHdr *p;
000611 for(p=pCache->pDirty; p; p=p->pDirtyNext){
000612 p->flags &= ~PGHDR_NEED_SYNC;
000613 }
000614 pCache->pSynced = pCache->pDirtyTail;
000615 }
000616
000617 /*
000618 ** Change the page number of page p to newPgno.
000619 */
000620 void sqlite3PcacheMove(PgHdr *p, Pgno newPgno){
000621 PCache *pCache = p->pCache;
000622 assert( p->nRef>0 );
000623 assert( newPgno>0 );
000624 assert( sqlite3PcachePageSanity(p) );
000625 pcacheTrace(("%p.MOVE %d -> %d\n",pCache,p->pgno,newPgno));
000626 sqlite3GlobalConfig.pcache2.xRekey(pCache->pCache, p->pPage, p->pgno,newPgno);
000627 p->pgno = newPgno;
000628 if( (p->flags&PGHDR_DIRTY) && (p->flags&PGHDR_NEED_SYNC) ){
000629 pcacheManageDirtyList(p, PCACHE_DIRTYLIST_FRONT);
000630 }
000631 }
000632
000633 /*
000634 ** Drop every cache entry whose page number is greater than "pgno". The
000635 ** caller must ensure that there are no outstanding references to any pages
000636 ** other than page 1 with a page number greater than pgno.
000637 **
000638 ** If there is a reference to page 1 and the pgno parameter passed to this
000639 ** function is 0, then the data area associated with page 1 is zeroed, but
000640 ** the page object is not dropped.
000641 */
000642 void sqlite3PcacheTruncate(PCache *pCache, Pgno pgno){
000643 if( pCache->pCache ){
000644 PgHdr *p;
000645 PgHdr *pNext;
000646 pcacheTrace(("%p.TRUNCATE %d\n",pCache,pgno));
000647 for(p=pCache->pDirty; p; p=pNext){
000648 pNext = p->pDirtyNext;
000649 /* This routine never gets call with a positive pgno except right
000650 ** after sqlite3PcacheCleanAll(). So if there are dirty pages,
000651 ** it must be that pgno==0.
000652 */
000653 assert( p->pgno>0 );
000654 if( p->pgno>pgno ){
000655 assert( p->flags&PGHDR_DIRTY );
000656 sqlite3PcacheMakeClean(p);
000657 }
000658 }
000659 if( pgno==0 && pCache->nRefSum ){
000660 sqlite3_pcache_page *pPage1;
000661 pPage1 = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache,1,0);
000662 if( ALWAYS(pPage1) ){ /* Page 1 is always available in cache, because
000663 ** pCache->nRefSum>0 */
000664 memset(pPage1->pBuf, 0, pCache->szPage);
000665 pgno = 1;
000666 }
000667 }
000668 sqlite3GlobalConfig.pcache2.xTruncate(pCache->pCache, pgno+1);
000669 }
000670 }
000671
000672 /*
000673 ** Close a cache.
000674 */
000675 void sqlite3PcacheClose(PCache *pCache){
000676 assert( pCache->pCache!=0 );
000677 pcacheTrace(("%p.CLOSE\n",pCache));
000678 sqlite3GlobalConfig.pcache2.xDestroy(pCache->pCache);
000679 }
000680
000681 /*
000682 ** Discard the contents of the cache.
000683 */
000684 void sqlite3PcacheClear(PCache *pCache){
000685 sqlite3PcacheTruncate(pCache, 0);
000686 }
000687
000688 /*
000689 ** Merge two lists of pages connected by pDirty and in pgno order.
000690 ** Do not bother fixing the pDirtyPrev pointers.
000691 */
000692 static PgHdr *pcacheMergeDirtyList(PgHdr *pA, PgHdr *pB){
000693 PgHdr result, *pTail;
000694 pTail = &result;
000695 assert( pA!=0 && pB!=0 );
000696 for(;;){
000697 if( pA->pgno<pB->pgno ){
000698 pTail->pDirty = pA;
000699 pTail = pA;
000700 pA = pA->pDirty;
000701 if( pA==0 ){
000702 pTail->pDirty = pB;
000703 break;
000704 }
000705 }else{
000706 pTail->pDirty = pB;
000707 pTail = pB;
000708 pB = pB->pDirty;
000709 if( pB==0 ){
000710 pTail->pDirty = pA;
000711 break;
000712 }
000713 }
000714 }
000715 return result.pDirty;
000716 }
000717
000718 /*
000719 ** Sort the list of pages in accending order by pgno. Pages are
000720 ** connected by pDirty pointers. The pDirtyPrev pointers are
000721 ** corrupted by this sort.
000722 **
000723 ** Since there cannot be more than 2^31 distinct pages in a database,
000724 ** there cannot be more than 31 buckets required by the merge sorter.
000725 ** One extra bucket is added to catch overflow in case something
000726 ** ever changes to make the previous sentence incorrect.
000727 */
000728 #define N_SORT_BUCKET 32
000729 static PgHdr *pcacheSortDirtyList(PgHdr *pIn){
000730 PgHdr *a[N_SORT_BUCKET], *p;
000731 int i;
000732 memset(a, 0, sizeof(a));
000733 while( pIn ){
000734 p = pIn;
000735 pIn = p->pDirty;
000736 p->pDirty = 0;
000737 for(i=0; ALWAYS(i<N_SORT_BUCKET-1); i++){
000738 if( a[i]==0 ){
000739 a[i] = p;
000740 break;
000741 }else{
000742 p = pcacheMergeDirtyList(a[i], p);
000743 a[i] = 0;
000744 }
000745 }
000746 if( NEVER(i==N_SORT_BUCKET-1) ){
000747 /* To get here, there need to be 2^(N_SORT_BUCKET) elements in
000748 ** the input list. But that is impossible.
000749 */
000750 a[i] = pcacheMergeDirtyList(a[i], p);
000751 }
000752 }
000753 p = a[0];
000754 for(i=1; i<N_SORT_BUCKET; i++){
000755 if( a[i]==0 ) continue;
000756 p = p ? pcacheMergeDirtyList(p, a[i]) : a[i];
000757 }
000758 return p;
000759 }
000760
000761 /*
000762 ** Return a list of all dirty pages in the cache, sorted by page number.
000763 */
000764 PgHdr *sqlite3PcacheDirtyList(PCache *pCache){
000765 PgHdr *p;
000766 for(p=pCache->pDirty; p; p=p->pDirtyNext){
000767 p->pDirty = p->pDirtyNext;
000768 }
000769 return pcacheSortDirtyList(pCache->pDirty);
000770 }
000771
000772 /*
000773 ** Return the total number of references to all pages held by the cache.
000774 **
000775 ** This is not the total number of pages referenced, but the sum of the
000776 ** reference count for all pages.
000777 */
000778 int sqlite3PcacheRefCount(PCache *pCache){
000779 return pCache->nRefSum;
000780 }
000781
000782 /*
000783 ** Return the number of references to the page supplied as an argument.
000784 */
000785 int sqlite3PcachePageRefcount(PgHdr *p){
000786 return p->nRef;
000787 }
000788
000789 /*
000790 ** Return the total number of pages in the cache.
000791 */
000792 int sqlite3PcachePagecount(PCache *pCache){
000793 assert( pCache->pCache!=0 );
000794 return sqlite3GlobalConfig.pcache2.xPagecount(pCache->pCache);
000795 }
000796
000797 #ifdef SQLITE_TEST
000798 /*
000799 ** Get the suggested cache-size value.
000800 */
000801 int sqlite3PcacheGetCachesize(PCache *pCache){
000802 return numberOfCachePages(pCache);
000803 }
000804 #endif
000805
000806 /*
000807 ** Set the suggested cache-size value.
000808 */
000809 void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
000810 assert( pCache->pCache!=0 );
000811 pCache->szCache = mxPage;
000812 sqlite3GlobalConfig.pcache2.xCachesize(pCache->pCache,
000813 numberOfCachePages(pCache));
000814 }
000815
000816 /*
000817 ** Set the suggested cache-spill value. Make no changes if if the
000818 ** argument is zero. Return the effective cache-spill size, which will
000819 ** be the larger of the szSpill and szCache.
000820 */
000821 int sqlite3PcacheSetSpillsize(PCache *p, int mxPage){
000822 int res;
000823 assert( p->pCache!=0 );
000824 if( mxPage ){
000825 if( mxPage<0 ){
000826 mxPage = (int)((-1024*(i64)mxPage)/(p->szPage+p->szExtra));
000827 }
000828 p->szSpill = mxPage;
000829 }
000830 res = numberOfCachePages(p);
000831 if( res<p->szSpill ) res = p->szSpill;
000832 return res;
000833 }
000834
000835 /*
000836 ** Free up as much memory as possible from the page cache.
000837 */
000838 void sqlite3PcacheShrink(PCache *pCache){
000839 assert( pCache->pCache!=0 );
000840 sqlite3GlobalConfig.pcache2.xShrink(pCache->pCache);
000841 }
000842
000843 /*
000844 ** Return the size of the header added by this middleware layer
000845 ** in the page-cache hierarchy.
000846 */
000847 int sqlite3HeaderSizePcache(void){ return ROUND8(sizeof(PgHdr)); }
000848
000849 /*
000850 ** Return the number of dirty pages currently in the cache, as a percentage
000851 ** of the configured cache size.
000852 */
000853 int sqlite3PCachePercentDirty(PCache *pCache){
000854 PgHdr *pDirty;
000855 int nDirty = 0;
000856 int nCache = numberOfCachePages(pCache);
000857 for(pDirty=pCache->pDirty; pDirty; pDirty=pDirty->pDirtyNext) nDirty++;
000858 return nCache ? (int)(((i64)nDirty * 100) / nCache) : 0;
000859 }
000860
000861 #ifdef SQLITE_DIRECT_OVERFLOW_READ
000862 /*
000863 ** Return true if there are one or more dirty pages in the cache. Else false.
000864 */
000865 int sqlite3PCacheIsDirty(PCache *pCache){
000866 return (pCache->pDirty!=0);
000867 }
000868 #endif
000869
000870 #if defined(SQLITE_CHECK_PAGES) || defined(SQLITE_DEBUG)
000871 /*
000872 ** For all dirty pages currently in the cache, invoke the specified
000873 ** callback. This is only used if the SQLITE_CHECK_PAGES macro is
000874 ** defined.
000875 */
000876 void sqlite3PcacheIterateDirty(PCache *pCache, void (*xIter)(PgHdr *)){
000877 PgHdr *pDirty;
000878 for(pDirty=pCache->pDirty; pDirty; pDirty=pDirty->pDirtyNext){
000879 xIter(pDirty);
000880 }
000881 }
000882 #endif