Module 12

module12/README.md

@@ -0,0 +1,168 @@
+## dwb_slots_hash_insert ()
+
+```C
+/*
+ * dwb_slots_hash_insert () - Insert entry in slots hash.
+ *
+ * return   : Error code.
+ * thread_p (in): The thread entry.
+ * vpid(in): The page identifier.
+ * slot(in): The DWB slot.
+ * inserted (out): 1, if slot inserted in hash.
+ */
+
+STATIC_INLINE int
+dwb_slots_hash_insert (THREAD_ENTRY * thread_p, VPID * vpid, DWB_SLOT * slot, bool * inserted)
+{
+  int error_code = NO_ERROR;
+  // NO_ERROR : 0 
+  DWB_SLOTS_HASH_ENTRY *slots_hash_entry = NULL;
+
+  assert (vpid != NULL && slot != NULL && inserted != NULL);
+  // vpid, slot, inserted == NULL -> crash
+
+  *inserted = dwb_Global.slots_hashmap.find_or_insert (thread_p, *vpid, slots_hash_entry);
+/*
+ * lf_hash_find_or_insert () - find or insert an entry in the hash table
+ vpid 를 key 값으로 dwb_global 변수의 slots_hashmap 변수에서 해쉬 함수를 사용해 value 를 가져오고 해쉬맵을 탐색한다.
+해쉬맵에서 slots_hash_entry 가 있으면 가져오고 inserted 0,
+없으면 thread_p의 freelist에서 받아와 해쉬맵에 추가하고 inserted 1로 설정한다.
+ */
+  assert (VPID_EQ (&slots_hash_entry->vpid, &slot->vpid));
+  /*
+  * #define VPID_EQ(vpid_ptr1,vpid_ptr2)
+  * ((vpid_ptr1) == (vpid_ptr2) || ((vpid_ptr1)->pageid == (vpid_ptr2)->pageid && (vpid_ptr1)->volid == (vpid_ptr2)->volid))
+  * 같은 주소를 가르키거나, 페이지 아이디가 같거나, volid가 같아야 한다.
+  */
+  assert (slots_hash_entry->vpid.pageid == slot->io_page->prv.pageid
+	  && slots_hash_entry->vpid.volid == slot->io_page->prv.volid);
+/*
+* prv.page id, prv.volid ? ? 
+*/
+  if (!(*inserted)) // *inserted == 0 인경우, find 한 경우
+    {
+      assert (slots_hash_entry->slot != NULL);
+	// slot == NULL -> crash
+      if (LSA_LT (&slot->lsa, &slots_hash_entry->slot->lsa))
+	  // log 는 순서대로 쌓인다.
+	  // slot의 lsa보다, slots_hash_entry의 lsa가 최신인 경우
+	  // 같은 정보가 중복으로 들어온 경우?
+	{
+	  dwb_log ("DWB hash find key (%d, %d), the LSA=(%lld,%d), better than (%lld,%d): \n",
+		   vpid->volid, vpid->pageid, slots_hash_entry->slot->lsa.pageid,
+		   slots_hash_entry->slot->lsa.offset, slot->lsa.pageid, slot->lsa.offset);
+	// The older slot is better than mine - leave it in hash.
+	  pthread_mutex_unlock (&slots_hash_entry->mutex); // unlock
+	  return NO_ERROR; // NO_ERROR 리턴
+	}
+      else if (LSA_EQ (&slot->lsa, &slots_hash_entry->slot->lsa))
+	{
+	  /*
+	   * If LSA's are equals, still replace slot in hash. We are in "flushing to disk without logging" case.
+	   * The page was modified but not logged. We have to flush this version since is the latest one.
+	   */
+	  // LSA 가 동일하더라도 해쉬의 슬롯을 바꾼다.
+	  // Page는 변경되었지만, 로그가 남지는 않았다. flush해야함.
+	  if (slots_hash_entry->slot->block_no == slot->block_no)
+	    {
+	      /* Invalidate the old slot, if is in the same block. We want to avoid duplicates in block at flush. */
+	      assert (slots_hash_entry->slot->position_in_block < slot->position_in_block);
+		  // slot->position_in_block이 더 최신임을 assert
+	      VPID_SET_NULL (&slots_hash_entry->slot->vpid);
+		  // hash 테이블에 있는 page id 를 null 로 바꿔줌
+	      fileio_initialize_res (thread_p, slots_hash_entry->slot->io_page, IO_PAGESIZE);
+			// 초기화
+	      dwb_log ("Found same page with same LSA in same block - %d - at positions (%d, %d) \n",
+		       slots_hash_entry->slot->position_in_block, slot->position_in_block);
+			// 로그 남겨줌
+	    }
+	  else // LSA 가 동일한데, block_no가 다를 때
+	    {
+#if !defined (NDEBUG) // No Debug?
+	      int old_block_no = ATOMIC_INC_32 (&slots_hash_entry->slot->block_no, 0);
+		  // slot_hash_enty의 block_no 반환
+	      if (old_block_no > 0)
+		{
+		  /* Be sure that the block containing old page version is flushed first. */
+		  DWB_BLOCK *old_block = &dwb_Global.blocks[old_block_no];
+		  DWB_BLOCK *new_block = &dwb_Global.blocks[slot->block_no];
+
+		  /* Maybe we will check that the slot is still in old block. */
+		  assert ((old_block->version < new_block->version)
+			  || (old_block->version == new_block->version && old_block->block_no < new_block->block_no));
+			  // new_block 이 더 최신임을 assert한다.
+
+		  dwb_log ("Found same page with same LSA in 2 different blocks old = (%d, %d), new = (%d,%d) \n",
+			   old_block_no, slots_hash_entry->slot->position_in_block, new_block->block_no,
+			   slot->position_in_block);
+		}
+#endif
+	    }
+	}
+
+      dwb_log ("Replace hash key (%d, %d), the new LSA=(%lld,%d), the old LSA = (%lld,%d)",
+	       vpid->volid, vpid->pageid, slot->lsa.pageid, slot->lsa.offset,
+	       slots_hash_entry->slot->lsa.pageid, slots_hash_entry->slot->lsa.offset);
+		   // 바꿀게라고 로그 표시
+    }
+  else // inserted가 됐을때
+    {
+      dwb_log ("Inserted hash key (%d, %d), LSA=(%lld,%d)", vpid->volid, vpid->pageid, slot->lsa.pageid,
+	       slot->lsa.offset);
+    }
+
+  slots_hash_entry->slot = slot; // 바꿔줌
+  pthread_mutex_unlock (&slots_hash_entry->mutex); // unlock
+  *inserted = true;
+
+  return NO_ERROR;
+}
+```
+
+### DWB_SLOTS_HASH_ENTRY
+
+```C
+/* Slots hash entry. */
+typedef struct dwb_slots_hash_entry DWB_SLOTS_HASH_ENTRY;
+struct dwb_slots_hash_entry
+{
+  VPID vpid;			/* Page VPID. */
+
+  DWB_SLOTS_HASH_ENTRY *stack;	/* Used in freelist. */
+  DWB_SLOTS_HASH_ENTRY *next;	/* Used in hash table. */
+  pthread_mutex_t mutex;	/* The mutex. */
+  UINT64 del_id;		/* Delete transaction ID (for lock free). */
+
+  DWB_SLOT *slot;		/* DWB slot containing a page. */
+
+  // *INDENT-OFF*
+  dwb_slots_hash_entry ()
+  {
+    pthread_mutex_init (&mutex, NULL);
+  }
+  ~dwb_slots_hash_entry ()
+  {
+    pthread_mutex_destroy (&mutex);
+  }
+  // *INDENT-ON*
+};
+```
+### LSA_LT
+``` C
+bool
+LSA_LT (const log_lsa *plsa1, const log_lsa *plsa2)
+{
+  assert (plsa1 != NULL && plsa2 != NULL);
+  return *plsa1 < *plsa2;
+}
+```
+
+### LSA_EQ
+```C
+bool
+LSA_EQ (const log_lsa *plsa1, const log_lsa *plsa2)
+{
+  assert (plsa1 != NULL && plsa2 != NULL);
+  return *plsa1 == *plsa2;
+}
+```