More efficient implementation of a lookaside allocator that supports mini (in this case, harcoded to 128B) slots.

FossilOrigin-Name: b02fdc09c838f355d9efce57f817d6a86153153b4a1f2b763914f4aaa34cb76e

1 files changed, 21 insertions, 1 deletions

diff --git a/src/main.c b/src/main.c
index 1afeee0bd..96234bfe4 100644
--- a/src/main.c
+++ b/src/main.c
@@ -683,6 +683,7 @@ int sqlite3_config(int op, ...){
 static int setupLookaside(sqlite3 *db, void *pBuf, int sz, int cnt){
 #ifndef SQLITE_OMIT_LOOKASIDE
   void *pStart;
+  sqlite3_int64 szAlloc = sz*(sqlite3_int64)cnt;
   
   if( sqlite3LookasideUsed(db,0)>0 ){
     return SQLITE_BUSY;
@@ -705,7 +706,7 @@ static int setupLookaside(sqlite3 *db, void *pBuf, int sz, int cnt){
     pStart = 0;
   }else if( pBuf==0 ){
     sqlite3BeginBenignMalloc();
-    pStart = sqlite3Malloc( sz*(sqlite3_int64)cnt );  /* IMP: R-61949-35727 */
+    pStart = sqlite3Malloc( szAlloc );  /* IMP: R-61949-35727 */
     sqlite3EndBenignMalloc();
     if( pStart ) cnt = sqlite3MallocSize(pStart)/sz;
   }else{
@@ -714,6 +715,15 @@ static int setupLookaside(sqlite3 *db, void *pBuf, int sz, int cnt){
   db->lookaside.pStart = pStart;
   db->lookaside.pInit = 0;
   db->lookaside.pFree = 0;
+#ifndef SQLITE_OMIT_MINI_LOOKASIDE
+  db->lookaside.pMiniInit = 0;
+  db->lookaside.pMiniFree = 0;
+  /* The arithmetic below causes the number of large lookaside slots to be 1/3
+  ** the number of mini slots, based on the observation that 75% of allocations
+  ** are <=128B.
+  */
+  cnt = szAlloc/(3*128+sz);
+#endif
   db->lookaside.sz = (u16)sz;
   db->lookaside.szTrue = (u16)sz;
   if( pStart ){
@@ -727,6 +737,16 @@ static int setupLookaside(sqlite3 *db, void *pBuf, int sz, int cnt){
       db->lookaside.pInit = p;
       p = (LookasideSlot*)&((u8*)p)[sz];
     }
+#ifndef SQLITE_OMIT_MINI_LOOKASIDE
+    db->lookaside.pMiddle = p;
+    /* Fill the remainder of the buffer with mini slots */
+    while(p<=(LookasideSlot*)&((u8*)pStart)[szAlloc-128]){
+      p->pNext = db->lookaside.pMiniInit;
+      db->lookaside.pMiniInit = p;
+      db->lookaside.nSlot++;
+      p = (LookasideSlot*)&((u8*)p)[128];
+    }
+#endif
     db->lookaside.pEnd = p;
     db->lookaside.bDisable = 0;
     db->lookaside.bMalloced = pBuf==0 ?1:0;