JDBC

JDBC

JDBC Catalogs in Doris are connected to external data sources using the standard JDBC protocol.

Once connected, Doris will ingest metadata of databases and tables from the external data sources in order to enable quick access to external data.

Usage

Supported datas sources include MySQL, PostgreSQL, Oracle, SQLServer, Clickhouse, Doris, SAP HANA, Trino and OceanBase.

Syntax

CREATE CATALOG <catalog_name>
PROPERTIES ("key"="value", ...)

Parameter Description

Parameter	Required or Not	Default Value	Description
user	Yes		Username in relation to the corresponding database
password	Yes		Password for the corresponding database
jdbc_url	Yes		JDBC connection string
driver_url	Yes		JDBC Driver Jar
driver_class	Yes		JDBC Driver Class
only_specified_database	No	"false"	Whether only the database specified to be synchronized.
lower_case_table_names	No	"false"	Whether to synchronize jdbc external data source table names in lower case.
include_database_list	No	""	When only_specified_database=true，only synchronize the specified databases. split with ','. db name is case sensitive.
exclude_database_list	No	""	When only_specified_database=true，do not synchronize the specified databases. split with ','. db name is case sensitive.

Driver path

driver_url can be specified in three ways:

1. File name. For example, mysql-connector-java-8.0.25.jar. Place the the JAR file in a directory jdbc_drivers under the Doris fe and be installation directories. I.e. create two directories /fe/jdbc_drivers and /be/jdbc_drivers and place a JAR file in each of them. You may have to create the jdbc_drivers directories manually. Make sure the directories are readable and preferably owned by the Doris user. You can change the location of the driver files by modifying the jdbc_drivers_dir property in the fe.conf and be.conf configuration files.

2. Local absolute path. For example, file:///path/to/mysql-connector-java-5.1.47.jar. Please place the Jar file package in the specified paths of FE/BE node.

3. HTTP address. For example, https://doris-community-test-1308700295.cos.ap-hongkong.myqcloud.com/jdbc_driver/mysql-connector-java-8.0.25.jar. The system will download the Driver file from the HTTP address. This only supports HTTP services with no authentication requirements.

Lowercase table name synchronization

When lower_case_table_names is set to true, Doris is able to query non-lowercase databases and tables by maintaining a mapping of lowercase names to actual names on the remote system

Notice:

1. In versions before Doris 2.0.3, it is only valid for Oracle database. When querying, all library names and table names will be converted to uppercase before querying Oracle, for example:

   Oracle has the TEST table in the TEST space. When Doris creates the Catalog, set lower_case_table_names to true, then Doris can query the TEST table through select * from oracle_catalog.test.test, and Doris will automatically format test.test into TEST.TEST is sent to Oracle. It should be noted that this is the default behavior, which also means that lowercase table names in Oracle cannot be queried.

   For other databases, you still need to specify the real library name and table name when querying.

2. In Doris 2.0.3 and later versions, it is valid for all databases. When querying, all library names and table names will be converted into real names and then queried. If you upgrade from an old version to 2.0. 3, Refresh <catalog_name> is required to take effect.

   However, if the database or table names differ only in case, such as Doris and doris, Doris cannot query them due to ambiguity.

3. When the FE parameter's lower_case_table_names is set to 1 or 2, the JDBC Catalog's lower_case_table_names parameter must be set to true. If the FE parameter's lower_case_table_names is set to 0, the JDBC Catalog parameter can be true or false and defaults to false. This ensures consistency and predictability in how Doris handles internal and external table configurations.

Specify synchronization database:

only_specified_database: When the JDBC is connected, you can specify which database/schema to connect. For example, you can specify the DataBase in mysql jdbc_url; you can specify the CurrentSchema in PG jdbc_url.

include_database_list: It only takes effect when only_specified_database=true, specify the database that needs to be synchronized, separated by ',', and the db name is case-sensitive.

exclude_database_list: It only takes effect when only specified database=true, specifies multiple databases that do not need to be synchronized, separated by ',', and the db name is case-sensitive.

When include_database_list and exclude_database_list specify overlapping databases, exclude_database_list would take effect with higher privilege over include_database_list.

If you connect the Oracle database when using this property, please use the version of the jar package above 8 or more (such as ojdbc8.jar).

Query

Example

select * from mysql_catalog.mysql_database.mysql_table where k1 > 1000 and k3 ='term';

tip

In some cases, the keywords in the database might be used as the field names. For queries to function normally in these cases, Doris will add escape characters to the field names and tables names in SQL statements based on the rules of different databases, such as (``) for MySQL, ([]) for SQLServer, and ("") for PostgreSQL and Oracle. This might require extra attention on case sensitivity. You can view the query statements sent to these various databases via explain sql.

Predicate Pushdown

1. When executing a query like where dt = '2022-01-01', Doris can push down these filtering conditions to the external data source, thereby directly excluding data that does not meet the conditions at the data source level, reducing the number of unqualified Necessary data acquisition and transfer. This greatly improves query performance while also reducing the load on external data sources.

2. When enable_func_pushdown is set to true, the function conditions after where will also be pushed down to the external data source. Currently, only MySQL, ClickHouse, and Oracle are supported. If you encounter functions that are not supported by MySQL, ClickHouse, and Oracle, you can use this The parameter is set to false. At present, Doris will automatically identify some functions that are not supported by MySQL and functions supported by ClickHouse and Oracle for push-down condition filtering. You can view them through explain sql.

Functions that are currently not pushed down include:

MYSQL
DATE_TRUNC
MONEY_FORMAT

Functions that are currently pushed down include:

ClickHouse
FROM_UNIXTIME
UNIX_TIMESTAMP

Oracle
NVL

Line Limit

If there is a limit keyword in the query, Doris will translate it into semantics suitable for different data sources.

Write Data

After the JDBC Catalog is established in Doris, you can write data directly through the insert into statement, or write the results of the query executed by Doris into the JDBC Catalog, or import data from one JDBC Catalog to another JDBC Catalog.

Example

insert into mysql_catalog.mysql_database.mysql_table values(1, "doris");
insert into mysql_catalog.mysql_database.mysql_table select * from table;

Transaction

In Doris, data is written to External Tables in batches. If the ingestion process is interrupted, rollbacks might be required. That's why JDBC Catalog Tables support data writing transactions. You can utilize this feature by setting the session variable: enable_odbc_transcation .

set enable_odbc_transcation = true; 

The transaction mechanism ensures the atomicity of data writing to JDBC External Tables, but it reduces performance to a certain extent. You may decide whether to enable transactions based on your own tradeoff.

Guide

MySQL

Example

• MySQL 5.7

CREATE CATALOG jdbc_mysql PROPERTIES (
    "type" = "jdbc",
    "user" = "root",
    "password" = "123456",
    "jdbc_url" = "jdbc:mysql://127.0.0.1:3306/demo",
    "driver_url" = "mysql-connector-java-5.1.47.jar",
    "driver_class" = "com.mysql.jdbc.Driver"
)

• MySQL 8

CREATE CATALOG jdbc_mysql PROPERTIES (
    "type" = "jdbc",
    "user" = "root",
    "password" = "123456",
    "jdbc_url" = "jdbc:mysql://127.0.0.1:3306/demo",
    "driver_url" = "mysql-connector-java-8.0.25.jar",
    "driver_class" = "com.mysql.cj.jdbc.Driver"
)

Hierarchy Mapping

Doris	MySQL
Catalog	MySQL Server
Database	Database
Table	Table

Type Mapping

MYSQL Type	Doris Type	Comment
BOOLEAN	TINYINT
TINYINT	TINYINT
SMALLINT	SMALLINT
MEDIUMINT	INT
INT	INT
BIGINT	BIGINT
UNSIGNED TINYINT	SMALLINT	Doris does not have an UNSIGNED data type, so expand by an order of magnitude
UNSIGNED MEDIUMINT	INT	Doris does not have an UNSIGNED data type, so expand by an order of magnitude
UNSIGNED INT	BIGINT	Doris does not have an UNSIGNED data type, so expand by an order of magnitude
UNSIGNED BIGINT	LARGEINT
FLOAT	FLOAT
DOUBLE	DOUBLE
DECIMAL	DECIMAL
UNSIGNED DECIMAL(p,s)	DECIMAL(p+1,s) / STRING	If p+1>38, the Doris STRING type will be used.
DATE	DATE
TIMESTAMP	DATETIME
DATETIME	DATETIME
YEAR	SMALLINT
TIME	STRING
CHAR	CHAR
VARCHAR	VARCHAR
JSON	JSON
SET	STRING
BIT	BOOLEAN/STRING	BIT(1) will be mapped to BOOLEAN, and other BITs will be mapped to STRING
TINYTEXT、TEXT、MEDIUMTEXT、LONGTEXT	STRING
BLOB、MEDIUMBLOB、LONGBLOB、TINYBLOB	STRING
TINYSTRING、STRING、MEDIUMSTRING、LONGSTRING	STRING
BINARY、VARBINARY	STRING
Other	UNSUPPORTED

PostgreSQL

Example

CREATE CATALOG jdbc_postgresql PROPERTIES (
    "type" = "jdbc",
    "user" = "root",
    "password" = "123456",
    "jdbc_url" = "jdbc:postgresql://127.0.0.1:5432/demo",
    "driver_url" = "postgresql-42.5.1.jar",
    "driver_class" = "org.postgresql.Driver"
);

Hierarchy Mapping

As for data mapping from PostgreSQL to Doris, one Database in Doris corresponds to one schema in the specified database in PostgreSQL (for example, "demo" in jdbc_url above), and one Table in that Database corresponds to one table in that schema. To make it more intuitive, the mapping relations are as follows:

Doris	PostgreSQL
Catalog	Database
Database	Schema
Table	Table

tip

Doris obtains all schemas that PG user can access through the SQL statement: select nspname from pg_namespace where has_schema_privilege('<UserName>', nspname, 'USAGE'); and map these schemas to doris database.

Type Mapping

POSTGRESQL Type	Doris Type	Comment
boolean	BOOLEAN
smallint/int2	SMALLINT
integer/int4	INT
bigint/int8	BIGINT
decimal/numeric	DECIMAL
real/float4	FLOAT
double precision	DOUBLE
smallserial	SMALLINT
serial	INT
bigserial	BIGINT
char	CHAR
varchar/text	STRING
timestamp	DATETIME
date	DATE
json/jsonb	JSON
time	STRING
interval	STRING
point/line/lseg/box/path/polygon/circle	STRING
cidr/inet/macaddr	STRING
bit	BOOLEAN/STRING	bit(1) will be mapped to BOOLEAN, and other bits will be mapped to STRING
uuid	STRING
Other	UNSUPPORTED

Oracle

Example

CREATE CATALOG jdbc_oracle PROPERTIES (
    "type" = "jdbc",
    "user" = "root",
    "password" = "123456",
    "jdbc_url" = "jdbc:oracle:thin:@127.0.0.1:1521:helowin",
    "driver_url" = "ojdbc8.jar",
    "driver_class" = "oracle.jdbc.driver.OracleDriver"
);

Hierarchy Mapping

As for data mapping from Oracle to Doris, one Database in Doris corresponds to one User, and one Table in that Database corresponds to one table that the User has access to. In conclusion, the mapping relations are as follows:

Doris	Oracle
Catalog	Database
Database	User
Table	Table

NOTE: Synchronizing Oracle's SYNONYM TABLE is not currently supported.

Type Mapping

ORACLE Type	Doris Type	Comment
number(p) / number(p,0)	TINYINT/SMALLINT/INT/BIGINT/LARGEINT	Doris will determine the type to map to based on the value of p: p < 3 -> TINYINT; p < 5 -> SMALLINT; p < 10 -> INT; p < 19 -> BIGINT; p > 19 -> LARGEINT
number(p,s), [ if(s>0 && p>s) ]	DECIMAL(p,s)
number(p,s), [ if(s>0 && p < s) ]	DECIMAL(s,s)
number(p,s), [ if(s<0) ]	TINYINT/SMALLINT/INT/BIGINT/LARGEINT	if s<0, Doris will set p to `p+
number		Doris does not support Oracle NUMBER type that does not specified p and s
float/real	DOUBLE
DATE	DATETIME
TIMESTAMP	DATETIME
CHAR/NCHAR	STRING
VARCHAR2/NVARCHAR2	STRING
LONG/ RAW/ LONG RAW/ INTERVAL	STRING
Other	UNSUPPORTED

SQLServer

Example

CREATE CATALOG jdbc_sqlserve PROPERTIES (
    "type" = "jdbc",
    "user" = "SA",
    "password"="Doris123456",
    "jdbc_url" = "jdbc:sqlserver://localhost:1433;DataBaseName=doris_test",
    "driver_url" = "mssql-jdbc-11.2.3.jre8.jar",
    "driver_class" = "com.microsoft.sqlserver.jdbc.SQLServerDriver"
);

Hierarchy Mapping

As for data mapping from SQLServer to Doris, one Database in Doris corresponds to one schema in the specified database in SQLServer (for example, "doris_test" in jdbc_url above), and one Table in that Database corresponds to one table in that schema. The mapping relations are as follows:

Doris	SQLServer
Catalog	Database
Database	Schema
Table	Table

Type Mapping

SQLServer Type	Doris Type	Comment
bit	BOOLEAN
tinyint	SMALLINT	SQLServer's tinyint is an unsigned number, so it maps to Doris' SMALLINT
smallint	SMALLINT
int	INT
bigint	BIGINT
real	FLOAT
float	DOUBLE
money	DECIMAL(19,4)
smallmoney	DECIMAL(10,4)
decimal/numeric	DECIMAL
date	DATE
datetime/datetime2/smalldatetime	DATETIMEV2
char/varchar/text/nchar/nvarchar/ntext	STRING
time/datetimeoffset	STRING
timestamp	STRING	Read the hexadecimal display of binary data, which has no practical significance.
Other	UNSUPPORTED

Doris

Jdbc Catalog also support to connect another Doris database:

• MySQL 5.7 Driver

CREATE CATALOG jdbc_doris PROPERTIES (
    "type" = "jdbc",
    "user" = "root",
    "password" = "123456",
    "jdbc_url" = "jdbc:mysql://127.0.0.1:9030?useSSL=false",
    "driver_url" = "mysql-connector-java-5.1.47.jar",
    "driver_class" = "com.mysql.jdbc.Driver"
)

• MySQL 8 Driver

CREATE CATALOG jdbc_doris PROPERTIES (
    "type" = "jdbc",
    "user" = "root",
    "password" = "123456",
    "jdbc_url" = "jdbc:mysql://127.0.0.1:9030?useSSL=false",
    "driver_url" = "mysql-connector-java-8.0.25.jar",
    "driver_class" = "com.mysql.cj.jdbc.Driver"
)

Type Mapping

Doris Type	Jdbc Catlog Doris Type	Comment
BOOLEAN	BOOLEAN
TINYINT	TINYINT
SMALLINT	SMALLINT
INT	INT
BIGINT	BIGINT
LARGEINT	LARGEINT
FLOAT	FLOAT
DOUBLE	DOUBLE
DECIMALV3	DECIMALV3/STRING	Which type will be selected according to the (precision, scale) of the DECIMAL field
DATE	DATE
DATETIME	DATETIME
CHAR	CHAR
VARCHAR	VARCHAR
STRING	STRING
TEXT	STRING
HLL	HLL	Query HLL needs to set return_object_data_as_binary=true
Array	Array	The internal type adaptation logic of Array refers to the above types, and nested complex types are not supported
BITMAP	BITMAP	Query BITMAP needs to set return_object_data_as_binary=true
Other	UNSUPPORTED

Clickhouse

Example

CREATE CATALOG jdbc_clickhouse PROPERTIES (
    "type" = "jdbc",
    "user" = "root",
    "password" = "123456",
    "jdbc_url" = "jdbc:clickhouse://127.0.0.1:8123/demo",
    "driver_url" = "clickhouse-jdbc-0.4.2-all.jar",
    "driver_class" = "com.clickhouse.jdbc.ClickHouseDriver"
);

Hierarchy Mapping

Doris	ClickHouse
Catalog	ClickHouse Server
Database	Database
Table	Table

Type Mapping

ClickHouse Type	Doris Type	Comment
Bool	BOOLEAN
String	STRING
Date/Date32	DATE
DateTime/DateTime64	DATETIME
Float32	FLOAT
Float64	DOUBLE
Int8	TINYINT
Int16/UInt8	SMALLINT	Doris does not have an UNSIGNED data type, so expand by an order of magnitude
Int32/UInt16	INT	Doris does not have an UNSIGNED data type, so expand by an order of magnitude
Int64/Uint32	BIGINT	Doris does not have an UNSIGNED data type, so expand by an order of magnitude
Int128/UInt64	LARGEINT	Doris does not have an UNSIGNED data type, so expand by an order of magnitude
Int256/UInt128/UInt256	STRING	Doris does not have a data type of this magnitude, and uses STRING for processing
DECIMAL	DECIMALV3/STRING	Which type will be selected according to the (precision, scale) of the DECIMAL field
Enum/IPv4/IPv6/UUID	STRING
Array	ARRAY	The internal type adaptation logic of Array refers to the above types, and does not support nested types
Other	UNSUPPORTED

SAP HANA

Example

CREATE CATALOG jdbc_hana PROPERTIES (
    "type" = "jdbc",
    "user" = "SYSTEM",
    "password" = "SAPHANA",
    "jdbc_url" = "jdbc:sap://localhost:31515/TEST",
    "driver_url" = "ngdbc.jar",
    "driver_class" = "com.sap.db.jdbc.Driver"
)

Hierarchy Mapping

Doris	SAP HANA
Catalog	Database
Database	Schema
Table	Table

Type Mapping

SAP HANA Type	Doris Type	Comment
BOOLEAN	BOOLEAN
TINYINT	TINYINT
SMALLINT	SMALLINT
INTERGER	INT
BIGINT	BIGINT
SMALLDECIMAL	DECIMALV3
DECIMAL	DECIMALV3/STRING	Which type will be selected according to the (precision, scale) of the DECIMAL field
REAL	FLOAT
DOUBLE	DOUBLE
DATE	DATE
TIME	STRING
TIMESTAMP	DATETIME
SECONDDATE	DATETIME
VARCHAR	STRING
NVARCHAR	STRING
ALPHANUM	STRING
SHORTTEXT	STRING
CHAR	CHAR
NCHAR	CHAR

Trino/Presto

Example

• Trino

CREATE CATALOG jdbc_trino PROPERTIES (
    "type" = "jdbc",
    "user" = "hadoop",
    "password" = "",
    "jdbc_url" = "jdbc:trino://localhost:9000/hive",
    "driver_url" = "trino-jdbc-389.jar",
    "driver_class" = "io.trino.jdbc.TrinoDriver"
);

• Presto

CREATE CATALOG jdbc_presto PROPERTIES (
    "type" = "jdbc",
    "user" = "hadoop",
    "password" = "",
    "jdbc_url" = "jdbc:presto://localhost:9000/hive",
    "driver_url" = "presto-jdbc-0.280.jar",
    "driver_class" = "com.facebook.presto.jdbc.PrestoDriver"
);

Hierarchy Mapping

When mapping Trino, Doris's Database corresponds to a Schema under the specified Catalog in Trino (such as "hive" in the jdbc_url parameter in the example). The Table under the Database of Doris corresponds to the Tables under the Schema in Trino. That is, the mapping relationship is as follows:

Doris	Trino/Presto
Catalog	Catalog
Database	Schema
Table	Table

Type Mapping

Trino/Presto Type	Doris Type	Comment
boolean	BOOLEAN
tinyint	TINYINT
smallint	SMALLINT
integer	INT
bigint	BIGINT
decimal	DECIMAL/DECIMALV3/STRING	Which type will be selected according to the (precision, scale) of the DECIMAL field
real	FLOAT
double	DOUBLE
date	DATE
timestamp	DATETIME
varchar	TEXT
char	CHAR
array	ARRAY	The internal type adaptation logic of Array refers to the above types, and does not support nested types
others	UNSUPPORTED

OceanBase

Example

CREATE CATALOG jdbc_oceanbase PROPERTIES (
    "type" = "jdbc",
    "user" = "root",
    "password" = "123456",
    "jdbc_url" = "jdbc:oceanbase://127.0.0.1:2881/demo",
    "driver_url" = "oceanbase-client-2.4.2.jar",
    "driver_class" = "com.oceanbase.jdbc.Driver"
)

tip

When Doris connects to OceanBase, it will automatically recognize that OceanBase is in MySQL or Oracle mode. Hierarchical correspondence and type mapping refer to MySQL and Oracle

View the JDBC Catalog

You can query all Catalogs in the current Doris cluster through SHOW CATALOGS:

SHOW CATALOGS;

Query the creation statement of a Catalog through SHOW CREATE CATALOG:

SHOW CREATE CATALOG <catalog_name>;

Drop the JDBC Catalog

A Catalog can be deleted via DROP CATALOG:

DROP CATALOG <catalog_name>;

Query the JDBC Catalog

1. Use SWITCH to switch the Catalog in effect for the current session:

   SWITCH <catalog_name>;

2. Query all libraries under the current Catalog through SHOW DATABASES:

   SHOW DATABASES FROM <catalog_name>;

   SHOW DATABASES;

3. Use USE to switch the Database that takes effect in the current session:

   USE <database_name>;

   Or directly use USE <catalog_name>.<database_name>; to switch the Database that takes effect in the current session

4. Query all tables under the current Catalog through SHOW TABLES:

   SHOW TABLES FROM <catalog_name>.<database_name>;

   SHOW TABLES FROM <database_name>;

   SHOW TABLES;

5. Query the data of a table under the current Catalog through SELECT:

   SELECT * FROM <table_name>;

FAQ

1. Are there any other databases supported besides MySQL, Oracle, PostgreSQL, SQLServer, ClickHouse, SAP HANA, Trino and OceanBase?

   Currently, Doris supports MySQL, Oracle, PostgreSQL, SQLServer, ClickHouse, SAP HANA, Trino and OceanBase. We are planning to expand this list. Technically, any databases that support JDBC access can be connected to Doris in the form of JDBC external tables. You are more than welcome to be a Doris contributor to expedite this effort.

2. Why does Mojibake occur when Doris tries to read emojis from MySQL external tables?

   In MySQL, utf8mb3 is the default utf8 format. It cannot represent emojis, which require 4-byte encoding. To solve this, when creating MySQL external tables, you need to set utf8mb4 encoding for the corresponding columns, set the server encoding to utf8mb4, and leave the characterEncoding in JDBC URl empty (because utf8mb4 is not supported for this property, and anything other than utf8mb4 will cause a failure to write the emojis).

   You can modify the configuration items globally:

   Modify the my.ini file in the mysql directory (for linux system, modify the my.cnf file in the etc directory)
   [client]
   default-character-set=utf8mb4
   
   [mysql]
   Set the mysql default character set
   default-character-set=utf8mb4
   
   [mysqld]
   Set the mysql character set server
   character-set-server=utf8mb4
   collation-server=utf8mb4_unicode_ci
   init_connect='SET NAMES utf8mb4
   
   Modify the type for the corresponding tables and columns
   ALTER TABLE table_name MODIFY  colum_name  VARCHAR(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
   ALTER TABLE table_name CHARSET=utf8mb4;
   SET NAMES utf8mb4

3. Exception occurs when reading MySQL date/datetime type

   ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.6)[INTERNAL_ERROR]UdfRuntimeException: get next block failed:
   CAUSED BY: SQLException: Zero date value prohibited
   CAUSED BY: DataReadException: Zero date value prohibited

   This is because the default handling of illegal Date/DateTime in JDBC is to throw an exception, and this behavior can be controlled through the parameter zeroDateTimeBehavior.

   The optional parameters are: EXCEPTION, CONVERT_TO_NULL, ROUND, respectively: exception error reporting, converted to NULL value, converted to "0001-01-01 00:00:00";

   You need to add zeroDateTimeBehavior=convertToNull to the end of the JDBC connection string when creating the Catalog jdbc_url, such as "jdbc_url" = "jdbc:mysql://127.0.0.1:3306/test?zeroDateTimeBehavior=convertToNull" In this case, JDBC will convert 0000-00-00 or 0000-00-00 00:00:00 into null, and then Doris will process all Date/DateTime type columns in the current Catalog as nullable types, so that It can be read normally.

4. When reading the MySQL table or other tables, a class loading failure occurs.

   Such as the following exception:

   failed to load driver class com.mysql.jdbc.driver in either of hikariconfig class loader

   This is because when creating the catalog, the driver_class filled in is incorrect and needs to be filled in correctly. For example, the above example has a case problem and should be filled in as "driver_class" = "com.mysql.jdbc.Driver"

5. Communication link abnormality occurs when reading MySQL

   If the following error occurs:

   ERROR 1105 (HY000): errCode = 2, detailMessage = PoolInitializationException: Failed to initialize pool: Communications link failure
   
   The last packet successfully received from the server was 7 milliseconds ago. The last packet sent successfully to the server was 4 milliseconds ago.
   CAUSED BY: CommunicationsException: Communications link failure
       
   The last packet successfully received from the server was 7 milliseconds ago. The last packet sent successfully to the server was 4 milliseconds ago.
   CAUSED BY: SSLHandshakeExcepti

   You can view be’s be.out log

   If the following information is included:

   WARN: Establishing SSL connection without server's identity verification is not recommended.
   According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set.
   For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'.
   You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.

   You can add ?useSSL=false to the end of the JDBC connection string when creating the Catalog, such as "jdbc_url" = "jdbc:mysql://127.0.0.1:3306/test?useSSL=false"

6. When using JDBC to query large amounts of MYSQL data, if the query is occasionally successful, the following error will occasionally be reported. When this error occurs, all MYSQL connections are disconnected and cannot be connected to MYSQL SERVER. After a while, mysql returns to normal. , but the previous connections are gone:

   ERROR 1105 (HY000): errCode = 2, detailMessage = [INTERNAL_ERROR]UdfRuntimeException: JDBC executor sql has error:
   CAUSED BY: CommunicationsException: Communications link failure
   The last packet successfully received from the server was 4,446 milliseconds ago. The last packet sent successfully to the server was 4,446 milliseconds ago.

   When the above phenomenon occurs, it may be that Mysql Server's own memory or CPU resources are exhausted, causing the Mysql service to be unavailable. You can try to increase the memory or CPU configuration of Mysql Server.

7. During the process of using JDBC to query MYSQL, if it is found that the query results are inconsistent with the query results in the MYSQL library

   First, check whether the string in the query field is case-sensitive. For example, there is a field c_1 in Table that contains two pieces of data: "aaa" and "AAA". If no distinguishing string is specified when initializing the MYSQL database, Case, then MYSQL is not case-sensitive in strings by default, but in Doris it is strictly case-sensitive, so the following situations will occur:

   Mysql behavior:
   select count(c_1) from table where c_1 = "aaa"; The string size is not distinguished, so the result is: 2
   
   Doris behavior:
   select count(c_1) from table where c_1 = "aaa"; strictly distinguishes the string size, so the result is: 1

   If the above phenomenon occurs, it needs to be adjusted according to needs, as follows:

   Add the "BINARY" keyword to force case sensitivity when querying in MYSQL: select count(c_1) from table where BINARY c_1 = "aaa"; or specify when creating a table in MYSQL: CREATE TABLE table ( c_1 VARCHAR(255) CHARACTER SET binary ); Or specify collation rules to make case sensitive when initializing the MYSQL database: character-set-server=UTF-8 and collation-server=utf8_bin.

8. Communication link abnormality occurs when reading SQL Server

   ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.6)[CANCELLED][INTERNAL_ERROR]UdfRuntimeException: Initialize datasource failed:
   CAUSED BY: SQLServerException: The driver could not establish a secure connection to SQL Server by using Secure Sockets Layer (SSL) encryption.
   Error: "sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException:
   unable to find valid certification path to requested target". ClientConnectionId:a92f3817-e8e6-4311-bc21-7c66

   You can add encrypt=false to the end of the JDBC connection string when creating the Catalog, such as "jdbc_url" = "jdbc:sqlserver://127.0.0.1:1433;DataBaseName=doris_test;encrypt=false"

9. Non supported character set (add orai18n.jar in your classpath): ZHS16GBK exception occurs when reading Oracle

   Download orai18n.jar and put it in the lib directory of Doris FE and the lib/java_extensions directory of BE (versions before Doris 2.0 It needs to be placed in the lib directory of BE).

   Starting from version 2.0.2, this file can be placed in the custom_lib/ directory of FE and BE (if it does not exist, just create it manually) to prevent the file from being lost when the lib directory is replaced when upgrading the cluster.

10. NoClassDefFoundError: net/jpountz/lz4/LZ4Factory error message appears when reading Clickhouse data through jdbc catalog

    You can download the lz4-1.3.0.jar package first, and then put it in DorisFE lib directory and BE's lib/lib/java_extensions directory (versions before Doris 2.0 need to be placed in BE's lib directory).

    Starting from version 2.0.2, this file can be placed in the custom_lib/ directory of FE and BE (if it does not exist, just create it manually) to prevent the file from being lost due to the replacement of the lib directory when upgrading the cluster.