more

source/libs/tdb/CMakeLists.txt

 # for tdb
-set(TDB_SUBDIRS "db")
-foreach(TDB_SUBDIR ${TDB_SUBDIRS})
-    aux_source_directory("src/${TDB_SUBDIR}" TDB_SRC)
-endforeach()
+# set(TDB_SUBDIRS "db")
+# foreach(TDB_SUBDIR ${TDB_SUBDIRS})
+#     aux_source_directory("src/${TDB_SUBDIR}" TDB_SRC)
+# endforeach()
 
-add_library(tdb STATIC ${TDB_SRC})
+add_library(tdb "")
+target_sources(tdb
+    PRIVATE
+    "src/db/tdbPgCache.c"
+)
 
 target_include_directories(
     tdb
@@ -29,5 +33,5 @@ target_include_directories(tdb_sqlite PUBLIC "src/sqliteinc")
 
 # for test
 if(${BUILD_TEST})
-    add_subdirectory(test)
+    # add_subdirectory(test)
 endif(${BUILD_TEST})

source/libs/tdb/src/db/tdbPgCache.c

@@ -14,567 +14,60 @@
  */
 #include "tdbInt.h"
 
-typedef TD_DLIST(SPage) SPgList;
-struct SPgCache {
-  TENV *  pEnv;  // TENV containing this page cache
-  pgsz_t  pgsize;
-  int32_t npage;
-  SPage **pages;
-  SPgList freeList;
-  SPgList lru;
-  struct {
-    int32_t  nbucket;
-    SPgList *buckets;
-  } pght;  // page hash table
+struct SPCache {
+  int             pageSize;
+  int             cacheSize;
+  int             extraSize;
+  int             nRef;
+  pthread_mutex_t mutex;
+  int             nPage;
+  SPgHdr *        lru;
+  int             nRecyclable;
+  int             nHash;
+  SPgHdr *        pgHash;
+  int             nFree;
+  SPgHdr *        pFree;
 };
 
-static void pgCachePinPage(SPage *pPage);
-static void pgCacheUnpinPage(SPage *pPage);
-
-int pgCacheOpen(SPgCache **ppPgCache, TENV *pEnv) {
-  SPgCache *pPgCache;
-  SPage *   pPage;
-  void *    pData;
-  pgsz_t    pgSize;
-  cachesz_t cacheSize;
-  int32_t   npage;
-  int32_t   nbucket;
-  size_t    msize;
-
-  *ppPgCache = NULL;
-  pgSize = tdbEnvGetPageSize(pEnv);
-  cacheSize = tdbEnvGetCacheSize(pEnv);
-  npage = cacheSize / pgSize;
-  nbucket = npage;
-  msize = sizeof(*pPgCache) + sizeof(SPage *) * npage + sizeof(SPgList) * nbucket;
-
-  // Allocate the handle
-  pPgCache = (SPgCache *)calloc(1, msize);
-  if (pPgCache == NULL) {
-    return -1;
-  }
-
-  // Init the handle
-  pPgCache->pEnv = pEnv;
-  pPgCache->pgsize = pgSize;
-  pPgCache->npage = npage;
-  pPgCache->pages = (SPage **)(&pPgCache[1]);
-  pPgCache->pght.nbucket = nbucket;
-  pPgCache->pght.buckets = (SPgList *)(&(pPgCache->pages[npage]));
-
-  TD_DLIST_INIT(&(pPgCache->freeList));
-
-  for (int32_t i = 0; i < npage; i++) {
-    pData = malloc(pgSize + sizeof(SPage));
-    if (pData == NULL) {
-      return -1;
-      // TODO: handle error
-    }
-
-    pPage = POINTER_SHIFT(pData, pgSize);
-
-    pPage->pgid = TDB_IVLD_PGID;
-    pPage->frameid = i;
-    pPage->pData = pData;
-
-    // add current page to the page cache
-    pPgCache->pages[i] = pPage;
-    TD_DLIST_APPEND_WITH_FIELD(&(pPgCache->freeList), pPage, freeNode);
-  }
-
-#if 0
-  for (int32_t i = 0; i < nbucket; i++) {
-    TD_DLIST_INIT(pPgCache->pght.buckets + i);
-  }
-#endif
-
-  *ppPgCache = pPgCache;
-  return 0;
-}
-
-int pgCacheClose(SPgCache *pPgCache) {
-  SPage *pPage;
-  if (pPgCache) {
-    for (int32_t i = 0; i < pPgCache->npage; i++) {
-      pPage = pPgCache->pages[i];
-      tfree(pPage->pData);
-    }
-
-    free(pPgCache);
-  }
-
-  return 0;
-}
-
-#define PG_CACHE_HASH(fileid, pgno)       \
-  ({                                      \
-    uint64_t *tmp = (uint64_t *)(fileid); \
-    (tmp[0] + tmp[1] + tmp[2] + (pgno));  \
-  })
-
-SPage *pgCacheFetch(SPgCache *pPgCache, pgid_t pgid) {
-  SPage *  pPage;
-  SPgFile *pPgFile;
-  SPgList *pBucket;
-
-  // 1. Search the page hash table SPgCache.pght
-  pBucket = pPgCache->pght.buckets + (PG_CACHE_HASH(pgid.fileid, pgid.pgno) % pPgCache->pght.nbucket);
-  pPage = TD_DLIST_HEAD(pBucket);
-  while (pPage && tdbCmprPgId(&(pPage->pgid), &pgid)) {
-    pPage = TD_DLIST_NODE_NEXT_WITH_FIELD(pPage, pghtNode);
-  }
-
-  if (pPage) {
-    // Page is found, pin the page and return the page
-    pgCachePinPage(pPage);
-    return pPage;
-  }
-
-  // 2. Check the free list
-  pPage = TD_DLIST_HEAD(&(pPgCache->freeList));
-  if (pPage) {
-    TD_DLIST_POP_WITH_FIELD(&(pPgCache->freeList), pPage, freeNode);
-    pgCachePinPage(pPage);
-    return pPage;
-  }
-
-  // 3. Try to recycle a page from the LRU list
-  pPage = TD_DLIST_HEAD(&(pPgCache->lru));
-  if (pPage) {
-    TD_DLIST_POP_WITH_FIELD(&(pPgCache->lru), pPage, lruNode);
-    // TODO: remove from the hash table
-    pgCachePinPage(pPage);
-    return pPage;
-  }
-
-  // 4. If a memory allocator is set, try to allocate from the allocator (TODO)
-
-  return NULL;
-}
-
-int pgCacheRelease(SPage *pPage) {
-  // TODO
-  return 0;
-}
-
-static void pgCachePinPage(SPage *pPage) {
-  // TODO
-}
-
-static void pgCacheUnpinPage(SPage *pPage) {
-  // TODO
-}
-
-#if 0
-// Exposed handle
-typedef struct TDB_MPOOL  TDB_MPOOL;
-typedef struct TDB_MPFILE TDB_MPFILE;
-
-typedef TD_DLIST_NODE(pg_t) pg_free_dlist_node_t, pg_hash_dlist_node_t;
-typedef struct pg_t {
-  SRWLatch             rwLatch;
-  frame_id_t           frameid;
-  pgid_t               pgid;
-  uint8_t              dirty;
-  uint8_t              rbit;
-  int32_t              pinRef;
-  pg_free_dlist_node_t free;
-  pg_hash_dlist_node_t hash;
-  void *               p;
-} pg_t;
-
-typedef TD_DLIST(pg_t) pg_list_t;
-typedef struct {
-  SRWLatch latch;
-  TD_DLIST(TDB_MPFILE);
-} mpf_bucket_t;
-struct TDB_MPOOL {
-  int64_t    cachesize;
-  pgsz_t     pgsize;
-  int32_t    npages;
-  pg_t *     pages;
-  pg_list_t  freeList;
-  frame_id_t clockHand;
-  struct {
-    int32_t    nbucket;
-    pg_list_t *hashtab;
-  } pgtab;  // page table, hash<pgid_t, pg_t>
-  struct {
-#define MPF_HASH_BUCKETS 16
-    mpf_bucket_t buckets[MPF_HASH_BUCKETS];
-  } mpfht;  // MPF hash table. MPFs using this MP will be put in this hash table
-};
-
-#define MP_PAGE_AT(mp, idx) (mp)->pages[idx]
-
-typedef TD_DLIST_NODE(TDB_MPFILE) td_mpf_dlist_node_t;
-struct TDB_MPFILE {
-  char *              fname;                    // file name
-  int                 fd;                       // fd
-  uint8_t             fileid[TDB_FILE_ID_LEN];  // file ID
-  TDB_MPOOL *         mp;                       // underlying memory pool
-  td_mpf_dlist_node_t node;
+struct SPgHdr {
+  void *  pData;
+  SPgid   pgid;
+  SPgHdr *pFreeNext;
 };
 
-/*=================================================== Exposed apis ==================================================*/
-// TDB_MPOOL
-int tdbMPoolOpen(TDB_MPOOL **mpp, uint64_t cachesize, pgsz_t pgsize);
-int tdbMPoolClose(TDB_MPOOL *mp);
-int tdbMPoolSync(TDB_MPOOL *mp);
-
-// TDB_MPFILE
-int tdbMPoolFileOpen(TDB_MPFILE **mpfp, const char *fname, TDB_MPOOL *mp);
-int tdbMPoolFileClose(TDB_MPFILE *mpf);
-int tdbMPoolFileNewPage(TDB_MPFILE *mpf, pgno_t *pgno, void *addr);
-int tdbMPoolFileFreePage(TDB_MPOOL *mpf, pgno_t *pgno, void *addr);
-int tdbMPoolFileGetPage(TDB_MPFILE *mpf, pgno_t pgno, void *addr);
-int tdbMPoolFilePutPage(TDB_MPFILE *mpf, pgno_t pgno, void *addr);
-int tdbMPoolFileSync(TDB_MPFILE *mpf);
-
-static void        tdbMPoolRegFile(TDB_MPOOL *mp, TDB_MPFILE *mpf);
-static void        tdbMPoolUnregFile(TDB_MPOOL *mp, TDB_MPFILE *mpf);
-static TDB_MPFILE *tdbMPoolGetFile(TDB_MPOOL *mp, uint8_t *fileid);
-static int         tdbMPoolFileReadPage(TDB_MPFILE *mpf, pgno_t pgno, void *p);
-static int         tdbMPoolFileWritePage(TDB_MPFILE *mpf, pgno_t pgno, const void *p);
-static void        tdbMPoolClockEvictPage(TDB_MPOOL *mp, pg_t **pagepp);
+int tdbOpenPCache(int pageSize, int cacheSize, int extraSize, SPCache **ppCache) {
+  SPCache *pCache;
+  void *   pPtr;
+  SPgHdr * pPgHdr;
 
-int tdbMPoolOpen(TDB_MPOOL **mpp, uint64_t cachesize, pgsz_t pgsize) {
-  TDB_MPOOL *mp = NULL;
-  size_t     tsize;
-  pg_t *     pagep;
-
-  // check parameters
-  if (!TDB_IS_PGSIZE_VLD(pgsize)) {
-    tdbError("invalid page size");
+  pCache = (SPCache *)calloc(1, sizeof(*pCache));
+  if (pCache == NULL) {
     return -1;
   }
 
-  // allocate handle
-  mp = (TDB_MPOOL *)calloc(1, sizeof(*mp));
-  if (mp == NULL) {
-    tdbError("failed to malloc memory pool handle");
-    goto _err;
-  }
-
-  // initialize the handle
-  mp->cachesize = cachesize;
-  mp->pgsize = pgsize;
-  mp->npages = cachesize / pgsize;
-  mp->clockHand = 0;
-
-  TD_DLIST_INIT(&mp->freeList);
-
-  mp->pages = (pg_t *)calloc(mp->npages, sizeof(pg_t));
-  if (mp->pages == NULL) {
-    tdbError("failed to malloc memory pool pages");
-    goto _err;
-  }
-
-  for (frame_id_t i = 0; i < mp->npages; i++) {
-    mp->pages[i].p = malloc(pgsize);
-    if (mp->pages[i].p == NULL) {
-      goto _err;
-    }
-
-    taosInitRWLatch(&mp->pages[i].rwLatch);
-    mp->pages[i].frameid = i;
-    mp->pages[i].pgid = TDB_IVLD_PGID;
-
-    // add new page to the free list
-    TD_DLIST_APPEND_WITH_FIELD(&(mp->freeList), &(mp->pages[i]), free);
-  }
-
-#define PGTAB_FACTOR 1.0
-  mp->pgtab.nbucket = mp->npages / PGTAB_FACTOR;
-  mp->pgtab.hashtab = (pg_list_t *)calloc(mp->pgtab.nbucket, sizeof(pg_list_t));
-  if (mp->pgtab.hashtab == NULL) {
-    tdbError("failed to malloc memory pool hash table");
-    goto _err;
-  }
-
-  // return
-  *mpp = mp;
-  return 0;
-
-_err:
-  tdbMPoolClose(mp);
-  *mpp = NULL;
-  return -1;
-}
-
-int tdbMPoolClose(TDB_MPOOL *mp) {
-  if (mp) {
-    tfree(mp->pgtab.hashtab);
-    if (mp->pages) {
-      for (int i = 0; i < mp->npages; i++) {
-        tfree(mp->pages[i].p);
-      }
-
-      free(mp->pages);
-    }
-
-    free(mp);
-  }
-  return 0;
-}
-
-int tdbMPoolFileOpen(TDB_MPFILE **mpfp, const char *fname, TDB_MPOOL *mp) {
-  TDB_MPFILE *mpf;
-
-  if ((mpf = (TDB_MPFILE *)calloc(1, sizeof(*mpf))) == NULL) {
-    return -1;
-  }
-
-  mpf->fd = -1;
-
-  if ((mpf->fname = strdup(fname)) == NULL) {
-    goto _err;
-  }
-
-  if ((mpf->fd = open(fname, O_CREAT | O_RDWR, 0755)) < 0) {
-    goto _err;
-  }
-
-  if (tdbGnrtFileID(fname, mpf->fileid, false) < 0) {
-    goto _err;
-  }
-
-  // Register current MPF to MP
-  tdbMPoolRegFile(mp, mpf);
-
-  *mpfp = mpf;
-  return 0;
-
-_err:
-  tdbMPoolFileClose(mpf);
-  *mpfp = NULL;
-  return -1;
-}
-
-int tdbMPoolFileClose(TDB_MPFILE *mpf) {
-  if (mpf) {
-    if (mpf->fd > 0) {
-      close(mpf->fd);
-    }
-    tfree(mpf->fname);
-    free(mpf);
-  }
-  return 0;
-}
+  pCache->pageSize = pageSize;
+  pCache->cacheSize = cacheSize;
+  pCache->extraSize = extraSize;
 
-#define MPF_GET_PAGE_BUCKETID(fileid, pgno, nbuckets) \
-  ({                                                  \
-    uint64_t *tmp = (uint64_t *)fileid;               \
-    (tmp[0] + tmp[1] + tmp[2] + (pgno)) % (nbuckets); \
-  })
+  pthread_mutex_init(&pCache->mutex, NULL);
 
-int tdbMPoolFileNewPage(TDB_MPFILE *mpf, pgno_t *pgno, void *addr) {
-  // TODO
-  return 0;
-}
-
-int tdbMPoolFileFreePage(TDB_MPOOL *mpf, pgno_t *pgno, void *addr) {
-  // TODO
-  return 0;
-}
-
-int tdbMPoolFileGetPage(TDB_MPFILE *mpf, pgno_t pgno, void *addr) {
-  pg_t *     pagep;
-  TDB_MPOOL *mp;
-  pg_list_t *pglist;
-
-  mp = mpf->mp;
-
-  // check if the page already in pool
-  pglist = mp->pgtab.hashtab + MPF_GET_PAGE_BUCKETID(mpf->fileid, pgno, mp->pgtab.nbucket);
-  pagep = TD_DLIST_HEAD(pglist);
-  while (pagep) {
-    if (memcmp(mpf->fileid, pagep->pgid.fileid, TDB_FILE_ID_LEN) == 0 && pgno == pagep->pgid.pgno) {
-      break;
-    }
-
-    pagep = TD_DLIST_NODE_NEXT_WITH_FIELD(pagep, hash);
-  }
-
-  if (pagep) {
-    // page is found
-    // todo: pin the page and return
-    *(void **)addr = pagep->p;
-    return 0;
-  }
-
-  // page not found
-  pagep = TD_DLIST_HEAD(&mp->freeList);
-  if (pagep) {
-    // has free page
-    TD_DLIST_POP_WITH_FIELD(&(mp->freeList), pagep, free);
-  } else {
-    // no free page available
-    tdbMPoolClockEvictPage(mp, &pagep);
-    if (pagep) {
-      if (pagep->dirty) {
-        // TODO: Handle dirty page eviction
-      }
+  for (int i = 0; i < cacheSize; i++) {
+    pPtr = calloc(1, pageSize + extraSize + sizeof(SPgHdr));
+    if (pPtr == NULL) {
+      return -1;
     }
-  }
 
-  if (pagep == NULL) {
-    // no available container page
-    return -1;
-  }
+    pPgHdr = (SPgHdr *)&((char *)pPtr)[pageSize + extraSize];
+    pPgHdr->pFreeNext = pCache->pFree;
+    pCache->pFree = pPgHdr;
 
-  // load page from the disk if a container page is available
-  // TODO: load the page from the disk
-  if (tdbMPoolFileReadPage(mpf, pgno, pagep->p) < 0) {
-    return -1;
+    pCache->nFree++;
   }
 
-  memcpy(pagep->pgid.fileid, mpf->fileid, TDB_FILE_ID_LEN);
-  pagep->pgid.pgno = pgno;
-  pagep->dirty = 0;
-  pagep->pinRef = 1;
-
-  // add current page to page table
-  TD_DLIST_APPEND_WITH_FIELD(pglist, pagep, hash);
-
   return 0;
 }
 
-int tdbMPoolFilePutPage(TDB_MPFILE *mpf, pgno_t pgno, void *addr) {
+int tdbClosePCache(SPCache *pCache) {
   // TODO
   return 0;
-}
-
-#define MPF_GET_BUCKETID(fileid)                   \
-  ({                                               \
-    uint64_t *tmp = (uint64_t *)fileid;            \
-    (tmp[0] + tmp[1] + tmp[2]) % MPF_HASH_BUCKETS; \
-  })
-
-static void tdbMPoolRegFile(TDB_MPOOL *mp, TDB_MPFILE *mpf) {
-  mpf_bucket_t *bktp;
-
-  bktp = mp->mpfht.buckets + MPF_GET_BUCKETID(mpf->fileid);
-
-  taosWLockLatch(&(bktp->latch));
-
-  TD_DLIST_APPEND_WITH_FIELD(bktp, mpf, node);
-
-  taosWUnLockLatch(&(bktp->latch));
-
-  mpf->mp = mp;
-}
-
-static TDB_MPFILE *tdbMPoolGetFile(TDB_MPOOL *mp, uint8_t *fileid) {
-  TDB_MPFILE *  mpf = NULL;
-  mpf_bucket_t *bktp;
-
-  bktp = mp->mpfht.buckets + MPF_GET_BUCKETID(fileid);
-
-  taosRLockLatch(&(bktp->latch));
-
-  mpf = TD_DLIST_HEAD(bktp);
-  while (mpf) {
-    if (memcmp(fileid, mpf->fileid, TDB_FILE_ID_LEN) == 0) {
-      break;
-    }
-
-    mpf = TD_DLIST_NODE_NEXT_WITH_FIELD(mpf, node);
-  }
-
-  taosRUnLockLatch(&(bktp->latch));
-
-  return mpf;
-}
-
-static void tdbMPoolUnregFile(TDB_MPOOL *mp, TDB_MPFILE *mpf) {
-  mpf_bucket_t *bktp;
-  TDB_MPFILE *  tmpf;
-
-  if (mpf->mp == NULL) return;
-
-  ASSERT(mpf->mp == mp);
-
-  bktp = mp->mpfht.buckets + MPF_GET_BUCKETID(mpf->fileid);
-
-  taosWLockLatch(&(bktp->latch));
-
-  tmpf = TD_DLIST_HEAD(bktp);
-
-  while (tmpf) {
-    if (memcmp(mpf->fileid, tmpf->fileid, TDB_FILE_ID_LEN) == 0) {
-      TD_DLIST_POP_WITH_FIELD(bktp, tmpf, node);
-      break;
-    }
-
-    tmpf = TD_DLIST_NODE_NEXT_WITH_FIELD(tmpf, node);
-  }
-
-  taosWUnLockLatch(&(bktp->latch));
-
-  ASSERT(tmpf == mpf);
-}
-
-static int tdbMPoolFileReadPage(TDB_MPFILE *mpf, pgno_t pgno, void *p) {
-  pgsz_t     pgsize;
-  TDB_MPOOL *mp;
-  off_t      offset;
-  size_t     rsize;
-
-  mp = mpf->mp;
-  pgsize = mp->pgsize;
-  offset = pgno * pgsize;
-
-  // TODO: use loop to read all data
-  rsize = pread(mpf->fd, p, pgsize, offset);
-  // TODO: error handle
-
-  return 0;
-}
-
-static int tdbMPoolFileWritePage(TDB_MPFILE *mpf, pgno_t pgno, const void *p) {
-  pgsz_t     pgsize;
-  TDB_MPOOL *mp;
-  off_t      offset;
-
-  mp = mpf->mp;
-  pgsize = mp->pgsize;
-  offset = pgno * pgsize;
-
-  lseek(mpf->fd, offset, SEEK_SET);
-  // TODO: handle error
-
-  write(mpf->fd, p, pgsize);
-  // TODO: handle error
-
-  return 0;
-}
-
-static void tdbMPoolClockEvictPage(TDB_MPOOL *mp, pg_t **pagepp) {
-  pg_t *     pagep;
-  frame_id_t och;
-
-  *pagepp = NULL;
-  och = mp->clockHand;
-
-  do {
-    pagep = mp->pages + mp->clockHand;
-    mp->clockHand = (mp->clockHand + 1) % mp->npages;
-
-    if (pagep->pinRef == 0) {
-      if (pagep->rbit == 1) {
-        pagep->rbit = 0;
-      } else {
-        break;
-      }
-    }
-
-    if (mp->clockHand == och) {
-      return;
-    }
-  } while (1);
-
-  *pagepp = pagep;
-}
-
-#endif
\ No newline at end of file
+}
\ No newline at end of file

source/libs/tdb/src/inc/tdbInt.h

@@ -38,7 +38,7 @@ typedef int32_t pgno_t;
 typedef struct {
   uint8_t fileid[TDB_FILE_ID_LEN];
   pgno_t  pgno;
-} pgid_t;
+} pgid_t, SPgid;
 
 #define TDB_IVLD_PGID (pgid_t){0, TDB_IVLD_PGNO};
 
@@ -65,9 +65,9 @@ static FORCE_INLINE int tdbCmprPgId(const void *p1, const void *p2) {
 typedef int32_t frame_id_t;
 
 // pgsz_t
-#define TDB_MIN_PGSIZE 512
-#define TDB_MAX_PGSIZE 65536
-#define TDB_DEFAULT_PGSIZE 4096
+#define TDB_MIN_PGSIZE       512
+#define TDB_MAX_PGSIZE       65536
+#define TDB_DEFAULT_PGSIZE   4096
 #define TDB_IS_PGSIZE_VLD(s) (((s) >= TDB_MIN_PGSIZE) && ((s) <= TDB_MAX_PGSIZE))
 
 // pgoff_t
@@ -119,13 +119,13 @@ typedef TD_DLIST_NODE(SPgFile) SPgFileListNode;
 
 #include "tdbUtil.h"
 
-#include "tdbBtree.h"
+// #include "tdbBtree.h"
 
 #include "tdbPgCache.h"
 
-#include "tdbPgFile.h"
+// #include "tdbPgFile.h"
 
-#include "tdbEnv.h"
+// #include "tdbEnv.h"
 
 #ifdef __cplusplus
 }

source/libs/tdb/src/inc/tdbPgCache.h

@@ -20,26 +20,12 @@
 extern "C" {
 #endif
 
-typedef struct SPgCache SPgCache;
-typedef struct SPage    SPage;
+typedef struct SPCache SPCache;
+typedef struct SPgHdr  SPgHdr;
 
-// SPgCache
-int pgCacheOpen(SPgCache **ppPgCache, TENV *pEnv);
-int pgCacheClose(SPgCache *pPgCache);
-
-SPage *pgCacheFetch(SPgCache *pPgCache, pgid_t pgid);
-int    pgCacheRelease(SPage *pPage);
-
-// SPage
-typedef TD_DLIST_NODE(SPage) SPgListNode;
-struct SPage {
-  pgid_t      pgid;      // page id
-  frame_id_t  frameid;   // frame id
-  uint8_t *   pData;     // real data
-  SPgListNode freeNode;  // for SPgCache.freeList
-  SPgListNode pghtNode;  // for pght
-  SPgListNode lruNode;   // for LRU
-};
+int   tdbOpenPCache(int pageSize, int cacheSize, int extraSize, SPCache **ppCache);
+int   tdbPCacheClose(SPCache *pCache);
+void *tdbPCacheFetch(SPCache *pCache);
 
 #ifdef __cplusplus
 }