背景
我有很多不同的东西＆＃34; （域特定项目/实体/主题）对于＆＃34;事物＆＃34;所有者（人类）。业主将要识别他们的东西＆＃34;有一个数字。而是显示一个大的＆＃34;随机＆＃34;我希望向他们展示一个对人类来说更容易的小数字（最好是从1开始的序列）。业主们很自在地谈论＆＃34;我的foo 37＆＃34;和＆＃34;她的酒吧128＆＃34;。那里＆＃34;序列＆＃34;可以有间隙，但附件号必须保持相同的＆＃34;＆＃34;意志力的一生。所以我需要一种方法来生成＆＃34; thing＆＃34; +所有者特定ID（当前称为＆＃34;可见ID＆＃34;）。
＆＃34;＆＃34;＆＃34; +所有者组合的规模为10k +。目前新的＆＃34;东西＆＃34;不能动态生成，但所有者可以。
一件事＆＃34;每个所有者的实例相对较小，每个所有者大约数十个，但是没有可以从业务规则中获得的硬性上限。新事物＆＃34;经常创建和删除实例。
考虑选项
我在一个问题Oracle Partitioned Sequence中找到了一个很好的讨论，它解决了我所遇到的几乎相同的问题。
到目前为止，我已考虑以下选项：
max(visible_id) + 1，但我们会遇到正常的并发问题，所以这是不行的。问题
是否有其他方法可以解决此问题，还是应该开始动态创建序列？如果序列是答案，请详细说明可能存在的陷阱（如DDL中的隐式提交）。
我对Oracle 11gR2和12c解决方案感兴趣（如果它们不同）。
用于说明问题的伪代码
create table foo (
id number primary key -- the key for computers
,owner_id number
,visible_id number -- the key for humans
,data_ varchar2(20)
);
create constraint foo_u1 unique foo(owner_id, visible_id);
-- primary key sequence
create sequence foo_id_seq;
insert into foo values(
foo_id_seq.nextval
,1
,1 -- what to put here ?
,'lorem ipsum'
);
insert into foo values(
foo_id_seq.nextval
,2
,1 -- what to put here ?
,'dolor sit amet'
);
select visible_id, data_ from foo where owner = 2 order by visible_id;
答案 0 :(得分：2)
由于差距正常，您应该实施＆＃34;选项2＆＃34;的变体。允许间隙意味着可以快速完成同步：竞争会话只需检查并继续，而不必等待其他人提交或回滚。
如果Oracle提供DBMS_LOCK选项，这将很容易。事实上，我可能会涉及CREATE OR REPLACE PACKAGE foo_api AS
PROCEDURE create_foo (p_owner_id NUMBER, p_data VARCHAR2);
END foo_api;
CREATE OR REPLACE PACKAGE BODY foo_api AS
-- We need to call allocate_unique in an autonomous transaction because
-- it commits and the calling program may not want to commit at this time
FUNCTION get_lock_handle (p_owner_id NUMBER, p_visible_id NUMBER)
RETURN VARCHAR2 IS
PRAGMA AUTONOMOUS_TRANSACTION;
l_lock_handle VARCHAR2 (128);
BEGIN
DBMS_LOCK.allocate_unique (
lockname => 'INSERT_FOO_' || p_owner_id || '_' || p_visible_id,
lockhandle => l_lock_handle
);
COMMIT;
RETURN l_lock_handle;
END;
PROCEDURE create_foo (p_owner_id NUMBER, p_data VARCHAR2) IS
-- This is the highest visible ID you'd ever want.
c_max_visible_id NUMBER := 1000;
BEGIN
<<id_loop>>
FOR r_available_ids IN (SELECT a.visible_id
FROM (SELECT ROWNUM visible_id
FROM DUAL
CONNECT BY ROWNUM <= c_max_visible_id) a
LEFT JOIN foo
ON foo.owner_id = p_owner_id
AND foo.visible_id = a.visible_id
WHERE foo.visible_id IS NULL) LOOP
-- We found a gap
-- We could try to insert into it. If another session has already done so and
-- committed, we'll get an ORA-00001. If another session has already done so but not
-- yet committed, we'll wait. And waiting is bad.
-- We'd like an INSERT...NO WAIT, but Oracle doesn't provide that.
-- Since this is the official API for creating foos and we have good application
-- design to ensure that foos are not created outside this API, we'll manage
-- the concurrency ourselves.
--
-- Try to acquire a user lock on the key we're going to try an insert.
DECLARE
l_lock_handle VARCHAR2 (128);
l_lock_result NUMBER;
l_seconds_to_wait NUMBER := 21600;
BEGIN
l_lock_handle := get_lock_handle (
p_owner_id => p_owner_id,
p_visible_id => r_available_ids.visible_id
);
l_lock_result := DBMS_LOCK.request (lockhandle => l_lock_handle,
lockmode => DBMS_LOCK.x_mode,
timeout => 0, -- Do not wait
release_on_commit => TRUE);
IF l_lock_result = 1 THEN
-- 1 => Timeout -- this could happen.
-- In this case, we want to move onto the next available ID.
CONTINUE id_loop;
END IF;
IF l_lock_result = 2 THEN
-- 2 => Deadlock (this should never happen, but scream if it does).
raise_application_error (
-20001,
'A deadlock occurred while trying to acquire Foo creation lock for '
|| p_owner_id
|| '_'
|| r_available_ids.visible_id
|| '. This is a programming error.');
END IF;
IF l_lock_result = 3 THEN
-- 3 => Parameter error (this should never happen, but scream if it does).
raise_application_error (
-20001,
'A parameter error occurred while trying to acquire Foo creation lock for '
|| p_owner_id
|| '_'
|| r_available_ids.visible_id
|| '. This is a programming error.');
END IF;
IF l_lock_result = 4 THEN
-- 4 => Already own lock (this should never happen, but scream if it does).
raise_application_error (
-20001,
'Attempted to create a Foo creation lock and found lock already held by session for '
|| p_owner_id
|| '_'
|| r_available_ids.visible_id
|| '. This is a programming error.');
END IF;
IF l_lock_result = 5 THEN
-- 5 => Illegal lock handle (this should never happen, but scream if it does).
raise_application_error (
-20001,
'An illegal lock handle error occurred while trying to acquire Foo creation lock for '
|| p_owner_id
|| '_'
|| r_available_ids.visible_id
|| '. This is a programming error.');
END IF;
END;
-- If we get here, we have an exclusive lock on the owner_id / visible_id
-- combination. Attempt the insert
BEGIN
INSERT INTO foo (id,
owner_id,
visible_id,
data_)
VALUES (foo_id_seq.NEXTVAL,
p_owner_id,
r_available_ids.visible_id,
p_data);
-- If we get here, we are done.
EXIT id_loop;
EXCEPTION
WHEN DUP_VAL_ON_INDEX THEN
-- Unfortunately, if this happened, we would have waited until the competing
-- session committed or rolled back. But the only way it
-- could have happened if the competing session did not use our API to create
-- or update the foo.
-- TODO: Do something to log or alert a programmer that this has happened,
-- but don't fail.
CONTINUE id_loop;
END;
END LOOP;
END create_foo;
END foo_api;
。以下是我对API的看法。
它对您所拥有的最大可见ID进行了一些假设，因为您在原始帖子中做出了这些假设。
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<executions>
<execution>
<id>default-test</id>
<goals>
<goal>test</goal>
</goals>
<configuration>
<argLine>-Xmx2048m -XX:MaxPermSize=512m</argLine>
<properties>
<property>
<name>listener</name>
<value>org.uncommons.reportng.HTMLReporter, org.uncommons.reportng.JUnitXMLReporter</value>
</property>
</properties>
<systemPropertyVariables>
<org.uncommons.reportng.title>OBS Test Suite</org.uncommons.reportng.title>
<org.uncommons.reportng.escape-output>false</org.uncommons.reportng.escape-output>
</systemPropertyVariables>
</configuration>
</execution>
</executions>
</plugin>
</plugins>