libsql-sqlite3: Optimize libsql_pager_has_codec() function

Cache the result of libsql_pager_has_codec() in Pager struct to avoid
walking through all VFSes every time a page is read.

Author: penberg

libsql-sqlite3/src/pager.c

@@ -630,6 +630,7 @@ struct Pager {
   u8 readOnly;                /* True for a read-only database */
   u8 memDb;                   /* True to inhibit all file I/O */
   u8 memVfs;                  /* VFS-implemented memory database */
+  u8 hasCodec;                /* True if pager has encryption codec */
 
   /**************************************************************************
   ** The following block contains those class members that change during
@@ -858,7 +859,7 @@ static const unsigned char aJournalMagic[] = {
 int sqlite3PagerDirectReadOk(Pager *pPager, Pgno pgno){
   if( pPager->fd->pMethods==0 ) return 0;
   if( sqlite3PCacheIsDirty(pPager->pPCache) ) return 0;
-  if( libsql_pager_has_codec(pPager) != 0 ) return 0;
+  if( pPager->hasCodec ) return 0;
 #ifndef SQLITE_OMIT_WAL
   if( pagerUseWal(pPager) ){
     u32 iRead = 0;
@@ -1081,7 +1082,7 @@ static void setGetterMethod(Pager *pPager){
   if( pPager->errCode ){
     pPager->xGet = getPageError;
 #if SQLITE_MAX_MMAP_SIZE>0
-  }else if( USEFETCH(pPager) && libsql_pager_has_codec(pPager) == 0 ){
+  }else if( USEFETCH(pPager) && !pPager->hasCodec ){
     pPager->xGet = getPageMMap;
 #endif /* SQLITE_MAX_MMAP_SIZE>0 */
   }else{
@@ -5103,6 +5104,8 @@ int sqlite3PagerOpen(
   /* pPager->xBusyHandler = 0; */
   /* pPager->pBusyHandlerArg = 0; */
   pPager->xReiniter = xReinit;
+  /* Cache the codec check result to avoid expensive VFS stack traversal on every page read */
+  pPager->hasCodec = libsql_pager_has_codec(pPager);
   setGetterMethod(pPager);
   /* memset(pPager->aHash, 0, sizeof(pPager->aHash)); */
   /* pPager->szMmap = SQLITE_DEFAULT_MMAP_SIZE // will be set by btree.c */