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PostgreSQL使用PreparedStatement导致查询慢的分析
实验环境：
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DB is PostgreSQL version 8.2.15
JDK1.8
测试一
使用JDBC查询一个SQL：
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public static void test1(String url, Properties props){
String sql = "SELECT l.src_ip, l.location_id, "
+ "SUM(l.us_bytes) as up_usage, "
+ "SUM(l.ds_bytes) as down_usage, "
+ "(SUM(l.us_bytes) + SUM(l.ds_bytes) ) as total_usage "
+ "FROM unmapped_endpoint_location_hours l "
+ "where l.org_id = 195078 "
+ "AND date_time >= '2017-04-01 00:00:00.0' AND date_time < '2017-04-08 00:00:00.0' "
+ "AND l.location_id in (2638,2640,2654 ) "
+ "GROUP BY l.src_ip, l.location_id ";
Connection conn = null;
Statement sta = null; try {
System.out.println("Start query1:" ); long s_time = System.currentTimeMillis();
conn = DriverManager.getConnection(url, props);
sta = conn.createStatement();
sta.execute(sql);
System.out.println("Using Time: " + (System.currentTimeMillis() - s_time));
} catch (SQLException e) {
e.printStackTrace();
} finally { if (conn != null) { try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
} if (sta != null) { try {
sta.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
结果：
Start query1:
Using Time: 11519 ms
测试二
使用JDBC PreparedStatement 查询相同的SQL：
public static void test2(String url, Properties props){
String sql2 = "SELECT l.src_ip, l.location_id, "
+ "SUM(l.us_bytes) as up_usage, "
+ "SUM(l.ds_bytes) as down_usage, "
+ "(SUM(l.us_bytes) + SUM(l.ds_bytes) ) as total_usage "
+ "FROM unmapped_endpoint_location_hours l "
+ "where l.org_id = ? "
+ "AND date_time >= ? AND date_time < ? "
+ "AND l.location_id in (2638,2640,2654 ) "
+ "GROUP BY l.src_ip, l.location_id";
Connection conn = null;
PreparedStatement preSta = null; try {
System.out.println("Start query2:"); long s_time = System.currentTimeMillis();
conn = DriverManager.getConnection(url, props);
preSta = conn.prepareStatement(sql2);
preSta.setString(1, "195078");
preSta.setString(2, "2017-04-01 00:00:00.0");
preSta.setString(3, "2017-04-09 00:00:00.0");
preSta.executeQuery();
System.out.println("Using Time: " + (System.currentTimeMillis() - s_time));
} catch (SQLException e) {
e.printStackTrace();
} finally { if (conn != null) { try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
} if (preSta != null) { try {
preSta.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
结果：
Start query2:
Using Time: 143031 ms
相同的SQL，测试二和测试一结果为什么差别这么大？
测试一的SQL没有使用PreparedStatement 方式，直接给了原始的SQL。测试二的使用了PreparedStatement ，但是在set参数的时候用的都是String。
两者查询速度相差10倍，这是不是很奇怪？
现在来做另一个实验：
测试三
使用JDBC PreparedStatement 查询相同的SQL：
public static void test3(String url, Properties props){
String sql2 = "SELECT l.src_ip, l.location_id, "
+ "SUM(l.us_bytes) as up_usage, "
+ "SUM(l.ds_bytes) as down_usage, "
+ "(SUM(l.us_bytes) + SUM(l.ds_bytes) ) as total_usage "
+ "FROM unmapped_endpoint_location_hours l "
+ "where l.org_id = ? "
+ "AND date_time >= ? AND date_time < ? "
+ "AND l.location_id in (2638,2640,2654 ) "
+ "GROUP BY l.src_ip, l.location_id";
Connection conn = null;
PreparedStatement preSta = null; try {
System.out.println("Start query3:"); long s_time = System.currentTimeMillis();
conn = DriverManager.getConnection(url, props);
preSta = conn.prepareStatement(sql2);
int org_id = 195078;
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
Date d1 = null;
Date d2 = null; try {
d1 = df.parse("2017-04-01 00:00:00");
d2 = df.parse("2017-04-09 00:00:00");
} catch (ParseException e1) {
e1.printStackTrace();
}
preSta.setInt(1, org_id);
preSta.setTimestamp(2, new java.sql.Timestamp(d1.getTime()));
preSta.setTimestamp(3, new java.sql.Timestamp(d2.getTime()));
preSta.executeQuery();
System.out.println("Using Time: " + (System.currentTimeMillis() - s_time));
} catch (SQLException e) {
e.printStackTrace();
} finally { if (conn != null) { try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
} if (preSta != null) { try {
preSta.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
结果：
Start query3:
Using Time: 16245 ms
测试结果和测试一的结果差不多，为什么？
这次测试同样使用了PreparedStatement，但是在设置参数的时候指定了参数的类型。
explan analyze
查看explan
dev=# explain analyze SELECT count(loc.name) AS totalNum dev-# FROM (SELECT t.src_ip, t.location_id, t.up_usage, t.down_usage, t.total_usage dev(# FROM (SELECT l.src_ip, l.location_id, dev(# SUM(l.us_bytes) as up_usage, dev(# SUM(l.ds_bytes) as down_usage, dev(# (SUM(l.us_bytes) + SUM(l.ds_bytes) ) as total_usage dev(# FROM unmapped_endpoint_location_hours l dev(# where l.org_id = 195078dev(# AND date_time >= '2017-04-11 00:00:00.0' AND date_time < '2017-04-20 00:00:00.0'dev(# AND l.location_id in (2638,2640) dev(# GROUP BY l.src_ip, l.location_id ) t dev(# WHERE t.total_usage > 0.0 ) m dev-# LEFT OUTER JOIN locations loc on m.location_id = loc.id WHERE loc.org_id = 195078;
Time: 15202.518 ms
Prepare Expalin: PREPARE test(int,text,text,int) as SELECT count(loc.name) AS totalNum FROM (SELECT t.src_ip, t.location_id, t.up_usage, t.down_usage, t.total_usage FROM (SELECT l.src_ip, l.location_id, SUM(l.us_bytes) as up_usage, SUM(l.ds_bytes) as down_usage, (SUM(l.us_bytes) + SUM(l.ds_bytes) ) as total_usage FROM unmapped_endpoint_location_hours l where l.org_id = $1 AND date_time >= $2 AND date_time < $3 AND l.location_id in (2638,2640) GROUP BY l.src_ip, l.location_id ) t WHERE t.total_usage > 0.0 ) m LEFT OUTER JOIN locations loc on m.location_id = loc.id WHERE loc.org_id = $4; Explain analyze EXECUTE test(195078,'2017-04-11 00:00:00.0','2017-04-20 00:00:00.0',195078); dev=# EXECUTE test(195078,'2017-04-11 00:00:00.0','2017-04-20 00:00:00.0',195078);
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