Remove some a small amount of redundant code related to PCache.pSynced from pcache.c.

FossilOrigin-Name: 9cc8cad78fdfe044ad6726ebfe6909c1e242fa55

diff --git a/manifest b/manifest
index a0a2ed640ac225132089d9be55278b9143283a21..a51e55cb83afc5bb123f3813a04ce3239a3aa942 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Do\snot\sreset\sthe\spage\scache\swhen\sa\srollback\sjournal\struncate\sfails,\sas\sdoing\nso\scan\scause\sloss\sof\sinformation\sfor\san\sin-memory\sTEMP\sfile.
-D 2016-05-11T12:47:46.752
+C Remove\ssome\sa\ssmall\samount\sof\sredundant\scode\srelated\sto\sPCache.pSynced\sfrom\spcache.c.
+D 2016-05-11T15:41:15.317
 F Makefile.in 9eda6e1c90d05c199c3ec8a7069b0682ad307657
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc db82b35aef27f412fef14d8534afc022138bcdfd
@@ -367,7 +367,7 @@ F src/os_win.h eb7a47aa17b26b77eb97e4823f20a00b8bda12ca
 F src/pager.c cb7a3990eabd895f6487c0856a7fec02b5e40faa
 F src/pager.h 329bdf078a4e0a3b35084534d58625d21fd03681
 F src/parse.y 10eb2f3fb62341291528c7984498054731f9d31e
-F src/pcache.c c128cafaac069e94931c3a743d5cf3d0c7b760d6
+F src/pcache.c 4af980bc2a987cf81ddbe867d238c9ccdbaac95c
 F src/pcache.h 6b865be765d1ebd06145219550b10921c7da7cc9
 F src/pcache1.c 7f51d2b541aab57596adf62db2c4bb025d34f04d
 F src/pragma.c faf42922bb7ab2f6672cb550356c1967abae3c84
@@ -1488,7 +1488,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 42fb6f1e99a6c31889819a0302679d598dc0ab1b
-R 6af21f51682f416bafd722831c805292
-U drh
-Z f092752ae332e4cfbb76f62bab02296e
+P 345ce1c9f64f2a424663b4dfcbe4586d9df7bff6
+R 410857f6cadf18a1818aed66391afc72
+U dan
+Z b239392669bc1d86adff0f06ee03f5ae

diff --git a/manifest.uuid b/manifest.uuid
index 39ea1115d0f7e90e1b0190783fa4a04d07f7b98b..9b2b37fae95508bafdd4da67ae09c3992981e459 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-345ce1c9f64f2a424663b4dfcbe4586d9df7bff6
\ No newline at end of file
+9cc8cad78fdfe044ad6726ebfe6909c1e242fa55
\ No newline at end of file

diff --git a/src/pcache.c b/src/pcache.c
index 7505547c2593f2073ac1ff291234a52c98880ceb..54b4044a01c8ebdf18586d6e2e6b103a7360248a 100644 (file)
--- a/src/pcache.c
+++ b/src/pcache.c
@@ -15,6 +15,22 @@
 
 /*
 ** A complete page cache is an instance of this structure.
+**
+** pDirty, pDirtyTail, pSynced:
+**   All dirty pages are linked into the doubly linked list using
+**   PgHdr.pDirtyNext and pDirtyPrev. The list is maintained in LRU order
+**   such that p was added to the list more recently than p->pDirtyNext.
+**   PCache.pDirty points to the first (newest) element in the list and
+**   pDirtyTail to the last (oldest).
+**
+**   The PCache.pSynced variable is used to optimize searching for a dirty
+**   page to eject from the cache mid-transaction. It is better to eject
+**   a page that does not require a journal sync than one that does. 
+**   Therefore, pSynced is maintained to that it *almost* always points
+**   to either the oldest page in the pDirty/pDirtyTail list that has a
+**   clear PGHDR_NEED_SYNC flag or to a page that is older than this one
+**   (so that the right page to eject can be found by following pDirtyPrev
+**   pointers).
 */
 struct PCache {
   PgHdr *pDirty, *pDirtyTail;         /* List of dirty pages in LRU order */
@@ -66,11 +82,7 @@ static void pcacheManageDirtyList(PgHdr *pPage, u8 addRemove){
   
     /* Update the PCache1.pSynced variable if necessary. */
     if( p->pSynced==pPage ){
-      PgHdr *pSynced = pPage->pDirtyPrev;
-      while( pSynced && (pSynced->flags&PGHDR_NEED_SYNC) ){
-        pSynced = pSynced->pDirtyPrev;
-      }
-      p->pSynced = pSynced;
+      p->pSynced = pPage->pDirtyPrev;
     }
   
     if( pPage->pDirtyNext ){
@@ -296,7 +308,11 @@ int sqlite3PcacheFetchStress(
     ** page that does not require a journal-sync (one with PGHDR_NEED_SYNC
     ** cleared), but if that is not possible settle for any other 
     ** unreferenced dirty page.
-    */
+    **
+    ** If the LRU page in the dirty list that has a clear PGHDR_NEED_SYNC
+    ** flag is currently referenced, then the following may leave pSynced
+    ** set incorrectly (pointing to other than the LRU page with NEED_SYNC
+    ** cleared). This is Ok, as pSynced is just an optimization.  */
     for(pPg=pCache->pSynced; 
         pPg && (pPg->nRef || (pPg->flags&PGHDR_NEED_SYNC)); 
         pPg=pPg->pDirtyPrev