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框架，特殊用户可以在其中制作报告。这些报告有时会构建大量查询，我们希望在其中即时解释并存储成本。这样我们可以在以后分析高成本查询并进行优化。
给我非法列异常的示例代码：
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));
}
用这个：
oracle = ConnectionManager.getConnection(ConnectionManager.Test);
stmt = oracle.createStatement()
stmt.execute("解释从 Dual 中选择 1 的计划");
rs = stmt.executeQuery("从表中选择plan_table_output(dbms_xplan.display())");
而（rs.next（））
{
System.out.println(rs.getString(1));
}
还有一种方法可以显示用于在此会话中运行最后一个查询的真实计划DBMS_XPLAN.DISPLAY_CURSOR。感兴趣的查询不需要在前面加上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，用户需要被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;
另请参阅https://blogs.oracle.com/optimizer/how-do-i-display-and-read-the-execution-plans-for-a-sql-statement。
但是我经历过，dbms_xplan.display_cursor()在执行查询之后立即调用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。
sql_id这可以通过在系统视图中搜索最新的v$sql并将其作为参数提供给dbms_xplan.display_cursor.
因此，这里有一个准备好使用 java 代码通过其 sql 记录最近执行的查询的实际执行计划（可能是部分的）。
public void explainActualPlan(String sql, boolean sqlIsPartial, Logger log) {
if (!log.isTraceEnabled()) return;
try (Connection connection = dataSource.getConnection()) {
String sqlId;
String sqlFilter = sqlIsPartial
? "sql_text like '%' || ? || '%'"
//+ " and parsing_schema_id = sys_context('USERENV', 'CURRENT_SCHEMAID')"
: (sql.length() <= 1000 ? "sql_text = ?" : "dbms_lob.compare(sql_fulltext, ?) = 0");
try (PreparedStatement st = connection.prepareStatement(
"select sql_id from v$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：
?为语法，因此使用 's 通过 sql 搜索将找不到任何匹配项:nv$sql?v$sql.sql_text（截断为前 1000 个字符）和（完整的 CLOB）都v$sql.sql_fulltext存储没有换行符的 sql 文本，因此如果您在查询文本中使用它们，可能需要执行连接V$SQLTEXT_WITH_NEWLINESLIKE匹配用于部分模式，因此可能需要转义'%' 和 '_' 特殊字符/*+ labuda FIRST_ROWS(200) */. 如果附录是有效标识符（字母数字并以字母开头），它仍会应用已知提示。通过将一些哈希码附加到提示子句，这对于跟踪感兴趣的查询可能很有用。v@sql可以另外过滤，and parsing_schema_id = sys_context('USERENV', 'CURRENT_SCHEMAID')但这会排除一些计划，以防数据库实例被不同模式中的几个类似应用程序使用，并且具有完全匹配的 sql 请求GATHER_PLAN_STATISTICS提示执行这是我的另一个答案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))