非常簡單的記錄，沒有可讀性，留作一個疑惑。

第一個節點更新資料塊
第二個節點更新同樣的資料塊
由於是更新操作，因此需要塊的current block
第二個節點像第一個節點要求current block，再傳送前，第一個節點需要pin住此塊，把log buffer內的內容寫磁碟。
統計量裡的gc current block pin time gc current block flush time分別對應了此種情況。但是我模擬的情況，發現並沒有發生統計量的增加。

節點1：
test@ILSP>select
2 statistic#,
3 name,
4 value
5 from
6 v$sysstat where statistic# in (215,216);

STATISTIC# NAME VALUE
---------- ---------------------------------------------------------------- ----------
215 gc current block pin time 68
216 gc current block flush time 7019

test@ILSP> update t_one set v1='10' where n1=265 and rownum=1;

1 row updated.

test@ILSP>
test@ILSP>select
2 statistic#,
3 name,
4 value
5 from
6 v$sysstat where statistic# in (215,216);

STATISTIC# NAME VALUE
---------- ---------------------------------------------------------------- ----------
215 gc current block pin time 68
216 gc current block flush time 7019

節點2：
test@ILSP>select
2 statistic#,
3 name,
4 value
5 from
6 v$sysstat where statistic# in (215,216);

STATISTIC# NAME VALUE
---------- ---------------------------------------------------------------- ----------
215 gc current block pin time 67
216 gc current block flush time 6906

test@ILSP> update t_one set v1='10' where n1=266 and rownum=1;

1 row updated.

test@ILSP>
test@ILSP>select
2 statistic#,
3 name,
4 value
5 from
6 v$sysstat where statistic# in (215,216);

STATISTIC# NAME VALUE
---------- ---------------------------------------------------------------- ----------
215 gc current block pin time 67
216 gc current block flush time 6906

但是，另一個場景卻發生了：

test@ILSP>begin
2 for i in 1 ..100000 loop
3 UPDATE wxh_tbd SET object_name=20 where rowid='AAAVaMAAEAAABDjAAA';
4 commit write immediate wait;
5 end loop;
6 end;
7 /

test@ILSP>begin
2 for i in 1 ..10000 loop
3 UPDATE wxh_tbd SET object_name=20 where rowid='AAAVaMAAEAAABDjAAB';
4 commit write immediate wait;
5 end loop;
6 end;
7 /

sys@ILSP>select
2 statistic#,
3 name,
4 value
5 from
6 v$sysstat where statistic# in (215,216);

STATISTIC# NAME VALUE
---------- ---------------------------------------------------------------- ----------
215 gc current block pin time 72
216 gc current block flush time 7502

2 rows selected.

sys@ILSP>/

STATISTIC# NAME VALUE
---------- ---------------------------------------------------------------- ----------
215 gc current block pin time 73
216 gc current block flush time 7545

2 rows selected.

sys@ILSP>/

STATISTIC# NAME VALUE
---------- ---------------------------------------------------------------- ----------
215 gc current block pin time 73
216 gc current block flush time 7570

2 rows selected.

sys@ILSP>/

STATISTIC# NAME VALUE
---------- ---------------------------------------------------------------- ----------
215 gc current block pin time 74
216 gc current block flush time 7591

我的版本是11.2.0.3，我的猜想，可能是ORACLE做了最佳化，再傳送current block前檢查下對應的日誌有沒有寫磁碟，如果已經寫磁碟了，就不需要再去做pin和flush的操作了。

gc current block pin time gc current block flush time 疑惑

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