一个语句，创建和源表格式相同并且带字段注释的表格方法：create table [if not exists] <table_name> like <existing_table_name> [lifecycle <days>];
而这个语句create table [if not exists] <table_name> as <select_statement>; 会创建一个新表，但是不会将源表的元数据复制到新表中.元数据包括列名、列类型、列注释、分区等信息。因此，使用这种方式创建的新表只会继承源表的列名和列类型，而不会继承源表的列注释。但是他会把源表所有数据插入新的表格。
示例：
CREATE TABLE IF NOT EXISTS table_name LIKE a.table_name;
create table if not exists table_name as select * from a.table_name;
docker run -m 4GB --rm openjdk:8-jre-slim java -XshowSettings:vm -version
docker run -m 4GB --rm openjdk:9-jre-slim java -XshowSettings:vm -version
docker run -m 4GB --rm openjdk:10-jre-slim java -XshowSettings:vm -version
docker run -m 4GB --rm openjdk:11-jre-slim java -XshowSettings:vm -version
docker run -m 4GB --rm openjdk:12 java -XshowSettings:vm -version
OpenJDK8（并没有识别容器限制，26.67G） 危险
[root@xiaoke-test ~]# docker run -m 4GB --rm openjdk:8-jre-slim java -XshowSettings:vm -version
VM settings:
Max. Heap Size (Estimated): 26.67G
Ergonomics Machine Class: server
Using VM: OpenJDK 64-Bit Server VM
openjdk version "1.8.0_181"
OpenJDK Runtime Environment (build 1.8.0_181-8u181-b13-2~deb9u1-b13)
OpenJDK 64-Bit Server VM (build 25.181-b13, mixed mode)
[root@xiaoke-test ~]# docker run -m 4GB --rm openjdk:8-jre-slim java -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -XshowSettings:vm -version
VM settings:
Max. Heap Size (Estimated): 910.50M
Ergonomics Machine Class: server
Using VM: OpenJDK 64-Bit Server VM
openjdk version "1.8.0_181"
OpenJDK Runtime Environment (build 1.8.0_181-8u181-b13-2~deb9u1-b13)
OpenJDK 64-Bit Server VM (build 25.181-b13, mixed mode)
OpenJDK 9（并没有识别容器限制，26.67G）危险
[root@xiaoke-test ~]# docker run -m 4GB --rm openjdk:9-jre-slim java -XshowSettings:vm -version
VM settings:
Max. Heap Size (Estimated): 29.97G
Using VM: OpenJDK 64-Bit Server VM
openjdk version "9.0.4"
OpenJDK Runtime Environment (build 9.0.4+12-Debian-4)
OpenJDK 64-Bit Server VM (build 9.0.4+12-Debian-4, mixed mode)
It protects you from software that accidentally creates zombie processes, which can (over time!) starve your entire system for PIDs (and make it unusable).
It ensures that the default signal handlers work for the software you run in your Docker image. For example, with Tini, SIGTERM properly terminates your process even if you didn’t explicitly install a signal handler for it.
It does so completely transparently! Docker images that work without Tini will work with Tini without any changes.
In Docker, you will want to use an entrypoint so you don’t have to remember to manually invoke Tini:
# Add Tini
ENV TINI_VERSION v0.19.0
ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini
RUN chmod +x /tini
ENTRYPOINT ["/tini", "--"]
# Run your program under Tini
CMD ["/your/program", "-and", "-its", "arguments"]
# or docker run your-image /your/program ...
