# 问题简介

```sql
SELECT TRUNC(COMPLETION_TIME) TIME,
       SUM(BLOCKS * BLOCK_SIZE) / 1024 / 1024  SIZE_MB,
       COUNT(*) num
  FROM V$ARCHIVED_LOG
 GROUP BY TRUNC(COMPLETION_TIME)
 ORDER BY 1;
```

这条 SQL 我们很熟悉，是用来统计每天生成的归档量的，但今天遇到了个奇怪的现象。

### 信息采集

**归档量**

```sql
TIME                   SIZE_MB        NUM
------------------- ---------- ----------
2021-10-09 00:00:00 21354.2207        162
2021-10-10 00:00:00 8132.05078         66
2021-10-11 00:00:00 106382.476        882

```

**存储使用情况**

```sql
SQL> SELECT GROUP_NUMBER GNO,
  2         NAME,
  3         TOTAL_MB/1024 TOTAL_GB,
  4         FREE_MB/1024 FREE_GB,
  5         FREE_MB / TOTAL_MB * 100 "FREE%",
  6         REQUIRED_MIRROR_FREE_MB RMFMB,
  7         USABLE_FILE_MB UFMB
  8    FROM V$ASM_DISKGROUP;

GNO NAME         TOTAL_GB    FREE_GB      FREE%      RMFMB       UFMB
---------- ---------- ---------- ---------- ---------- ---------- ----------
         1 ARCH              150  82.828125   55.21875          0      84816
         2 DATA             4000 926.681641  23.167041          0     948922
         3 OCR                30 29.0957031 96.9856771      10240       9777
```

**归档保存情况**

```
[grid@REGIONAL-DB-1:/home/grid +ASM1]$ asmcmd
ASMCMD> cd arch
ASMCMD> cd *
ASMCMD> cd *
ASMCMD> ls
2021_10_08/
2021_10_09/
2021_10_10/
2021_10_11/
ASMCMD> 
```

### 疑问

显示保留的三天的归档量，总量应该在 135G 左右，但是存储显示只是用了 70 G不到，计算出来的量约是实际占用的两倍，那么是归档的统计语句写错了？

# 原因

通过了解，这个库是一套 DG 的数据库，实际归档是两个归档路径（本地+远程DG库）所产生的归档总和

```sql
SQL> SELECT value FROM v$parameter WHERE NAME LIKE 'log_archive_dest__' and value is not null;

VALUE
-----------------------------------------------------------------------------------------
location=+ARCH valid_for=(all_logfiles,all_roles) db_unique_name=cender
service=tns_cender_sty lgwr async valid_for=(online_logfiles,primary_role) db_unique_name=cenderdg
```

所以我将原语句做了一个小的更改

```sql
SELECT TRUNC(COMPLETION_TIME) TIME,
       SUM(BLOCKS * BLOCK_SIZE) / 1024 / 1024 /
       ((SELECT COUNT(*)
           FROM v$parameter
          WHERE NAME LIKE 'log_archive_dest__'
            AND VALUE IS NOT NULL)) SIZE_MB,
       COUNT(*) num
  FROM V$ARCHIVED_LOG
 GROUP BY TRUNC(COMPLETION_TIME)
 ORDER BY 1;

TIME                   SIZE_MB        NUM
------------------- ---------- ----------
2021-10-09 00:00:00 10677.1104        162
2021-10-10 00:00:00 4066.02539         66
2021-10-11 00:00:00  53191.238        872
```

再考虑到有可能做完迁移，没有清理 DG 环境的可能性，所以又做了进一步的改写

```sql
SELECT TRUNC(COMPLETION_TIME) TIME,
       SUM(BLOCKS * BLOCK_SIZE) / 1024 / 1024 /
       ((SELECT COUNT(*)
           FROM v$parameter
          WHERE NAME LIKE 'log_archive_dest__'
            AND VALUE IS NOT NULL) -
        (SELECT COUNT(*) FROM v$archive_dest WHERE error IS NOT NULL)) SIZE_MB,
       COUNT(*) num
  FROM V$ARCHIVED_LOG
 GROUP BY TRUNC(COMPLETION_TIME)
 ORDER BY 1;
```

不足之处就是如果数据库归档到异地出现中断，因为没有实时跟踪异常，即有时异常，有时正常的话，统计就不准了。

ITPub博客

Oracle：归档量统计

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