我想知道如何使用Java获取解释计划。我需要这个的原因是因为我们有一个特殊用户可以制作报告的框架。这些报告有时会构建大量查询，我们希望在其中动态解释并存储成本。这样我们就可以在以后分析高成本查询并进行优化。
示例代码，它给出了非法列异常：
ResultSet rs = null;
try {
oracle = ConnectionManager.getConnection(ConnectionManager.Test);
pstmt = oracle.prepareStatement("begin execute immediate
'explain plan for SELECT 1 from Dual'; end;");
rs = pstmt.executeQuery();
while (rs.next()) {
System.out.println(rs.getString(1));
}
答案 0 :(得分：17)
使用此：
oracle = ConnectionManager.getConnection(ConnectionManager.Test);
stmt = oracle.createStatement()
stmt.execute("explain plan for SELECT 1 from Dual");
rs = stmt.executeQuery("select plan_table_output from table(dbms_xplan.display())");
while (rs.next())
{
System.out.println(rs.getString(1));
}
答案 1 :(得分：2)
还有一种方法可以通过DBMS_XPLAN.DISPLAY_CURSOR显示用于在此会话中运行上次查询的真实计划。感兴趣的查询不需要添加EXPLAIN PLAN FOR。
try (Statement st = connection.createStatement()) {
try (ResultSet rs = st.executeQuery(
"select plan_table_output from table(dbms_xplan.display_cursor())")) {
while (rs.next()) {
System.out.println(rs.getString(1));
}
}
}
请注意，需要为用户授予以下权限才能使用DBMS_XPLAN.DISPLAY_CURSOR：
GRANT SELECT ON v_$session TO USER;
GRANT SELECT ON v_$sql_plan TO USER;
GRANT SELECT ON v_$sql_plan_statistics_all TO USER;
GRANT SELECT ON v_$sql TO USER;
另见https://blogs.oracle.com/optimizer/how-do-i-display-and-read-the-execution-plans-for-a-sql-statement。
但是我经历过，在执行的查询之后立即调用dbms_xplan.display_cursor()可能仍会返回不相关的结果，以防多线程应用程序使用共享连接池。
可以通过搜索v$sql系统视图中的最新sql_id并将其作为参数提供给dbms_xplan.display_cursor来解决此问题。
所以这里是一个随时可以使用java代码来记录最近执行的查询的实际执行计划（可能是部分的）。
public void explainActualPlan(String sql, boolean sqlIsPartial, Logger log) {
if (!log.isTraceEnabled()) return;
try (Connection connection = dataSource.getConnection()) {
String sqlId;
String sqlFilter = sqlIsPartial
? "sql_text like '%' || ? || '%'"
//+ " and parsing_schema_id = sys_context('USERENV', 'CURRENT_SCHEMAID')"
: (sql.length() <= 1000 ? "sql_text = ?" : "dbms_lob.compare(sql_fulltext, ?) = 0");
try (PreparedStatement st = connection.prepareStatement(
"select sql_id from v$sql where " + sqlFilter +
" order by last_active_time desc fetch next 1 row only")) {
st.setString(1, sql);
try (ResultSet rs = st.executeQuery()) {
if (rs.next()) {
sqlId = rs.getString(1);
} else {
log.warn("Can't find sql_id for sql '{}'. Has it really been just executed?", sql);
return;
}
}
}
String planFormat = "TYPICAL";
if (sql.contains("GATHER_PLAN_STATISTICS")) {
planFormat += " ALLSTATS LAST +cost +bytes OUTLINE";
}
try (PreparedStatement st = connection.prepareStatement(
"select plan_table_output from table(dbms_xplan.display_cursor(" +
"sql_id => ?, format => '" + planFormat + "'))")) {
st.setString(1, sqlId);
try (ResultSet rs = st.executeQuery()) {
StringBuilder sb = new StringBuilder("Last query plan:\n");
while (rs.next()) {
sb.append(rs.getString(1)).append('\n');
}
log.trace(sb.toString());
}
}
} catch (Exception e) {
log.warn("Failed to explain query plan for '{}'", sql, e);
log.warn("Check that permissions are granted to the current db user:\n"
+ "GRANT SELECT ON v_$session TO <USER>;\n"
+ "GRANT SELECT ON v_$sql_plan TO <USER>;\n"
+ "GRANT SELECT ON v_$sql_plan_statistics_all TO <USER>;\n"
+ "GRANT SELECT ON v_$sql TO <USER>;\n"
);
}
}
一些注意事项：
?之前始终将准备好的语句参数从:n转换为v$sql语法，因此使用?的sql搜索将无法找到任何比赛v$sql.sql_text（截断到前1000个字符）和v$sql.sql_fulltext（完整CLOB）存储没有换行符的SQL文本，因此可能需要使用a join执行V$SQLTEXT_WITH_NEWLINES如果您在查询文本中使用它们LIKE匹配用于部分模式，因此可能需要escape'％'和'_'特殊字符/*+ labuda FIRST_ROWS(200) */。如果附录是有效的标识符（是字母数字并以字母开头），它仍然会应用已知的提示。这可以通过将一些哈希码附加到提示子句来跟踪感兴趣的查询。v@sql可以通过and parsing_schema_id = sys_context('USERENV', 'CURRENT_SCHEMAID')进行额外过滤，但如果数据库实例被不同模式中的几个类似应用程序用于完全匹配的sql请求，则会排除某些计划GATHER_PLAN_STATISTICS提示执行sql，上面的代码会提供计划输出中的其他详细信息以下是来自my another answer的查询的上述代码输出示例：
22:54:53.558 TRACE o.f.adminkit.AdminKitSelectorQuery - Last query plan:
SQL_ID c67mmq4wg49sx, child number 0
-------------------------------------
select * from (select * from (select /*+ FIRST_ROWS(200)
INDEX_RS_DESC("FR_MESSAGE_PART" ("TS")) GATHER_PLAN_STATISTICS */ "ID",
"MESSAGE_TYPE_ID", "TS", "REMOTE_ADDRESS", "TRX_ID",
"PROTOCOL_MESSAGE_ID", "MESSAGE_DATA_ID", "TEXT_OFFSET", "TEXT_SIZE",
"BODY_OFFSET", "BODY_SIZE", "INCOMING" from "FR_MESSAGE_PART" where
"TS" + 0 >= :1 and "TS" < :2 and "ID" >= 376894993815568384 and "ID" <
411234940974268416 order by "TS" DESC) where ROWNUM <= 200) offset 180
rows
Plan hash value: 2499404919
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |E-Bytes|E-Temp | Cost (%CPU)| E-Time | Pstart| Pstop | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | | | 640K(100)| | | | 20 |00:00:00.01 | 322 | | | |
|* 1 | VIEW | | 1 | 200 | 130K| | 640K (1)| 00:00:26 | | | 20 |00:00:00.01 | 322 | | | |
| 2 | WINDOW NOSORT | | 1 | 200 | 127K| | 640K (1)| 00:00:26 | | | 200 |00:00:00.01 | 322 | 142K| 142K| |
| 3 | VIEW | | 1 | 200 | 127K| | 640K (1)| 00:00:26 | | | 200 |00:00:00.01 | 322 | | | |
|* 4 | COUNT STOPKEY | | 1 | | | | | | | | 200 |00:00:00.01 | 322 | | | |
| 5 | VIEW | | 1 | 780K| 487M| | 640K (1)| 00:00:26 | | | 200 |00:00:00.01 | 322 | | | |
|* 6 | SORT ORDER BY STOPKEY | | 1 | 780K| 68M| 89M| 640K (1)| 00:00:26 | | | 200 |00:00:00.01 | 322 | 29696 | 29696 |26624 (0)|
| 7 | PARTITION RANGE ITERATOR | | 1 | 780K| 68M| | 624K (1)| 00:00:25 | 3 | 2 | 400 |00:00:00.01 | 322 | | | |
|* 8 | COUNT STOPKEY | | 2 | | | | | | | | 400 |00:00:00.01 | 322 | | | |
|* 9 | TABLE ACCESS BY LOCAL INDEX ROWID| FR_MESSAGE_PART | 2 | 780K| 68M| | 624K (1)| 00:00:25 | 3 | 2 | 400 |00:00:00.01 | 322 | | | |
|* 10 | INDEX RANGE SCAN DESCENDING | IX_FR_MESSAGE_PART_TS | 2 | 559K| | | 44368 (1)| 00:00:02 | 3 | 2 | 400 |00:00:00.01 | 8 | | | |
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('12.1.0.2')
DB_VERSION('12.1.0.2')
OPT_PARAM('optimizer_dynamic_sampling' 0)
OPT_PARAM('_optimizer_dsdir_usage_control' 0)
FIRST_ROWS(200)
OUTLINE_LEAF(@"SEL$3")
OUTLINE_LEAF(@"SEL$2")
OUTLINE_LEAF(@"SEL$1")
OUTLINE_LEAF(@"SEL$4")
NO_ACCESS(@"SEL$4" "from$_subquery$_004"@"SEL$4")
NO_ACCESS(@"SEL$1" "from$_subquery$_001"@"SEL$1")
NO_ACCESS(@"SEL$2" "from$_subquery$_002"@"SEL$2")
INDEX_RS_DESC(@"SEL$3" "FR_MESSAGE_PART"@"SEL$3" ("FR_MESSAGE_PART"."TS"))
END_OUTLINE_DATA
*/
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("from$_subquery$_004"."rowlimit_$$_rownumber">180)
4 - filter(ROWNUM<=200)
6 - filter(ROWNUM<=200)
8 - filter(ROWNUM<=200)
9 - filter("ID">=376894993815568384)
10 - access("TS"<:2)
filter((INTERNAL_FUNCTION("TS")+0>=:1 AND "TS"<:2))