postgres-fdw 集成cratedb 的尝试的几个问题
尽管cratedb 支持pg 协议但是不是100%兼容的（不像yugabyte db，基于pg）所以进行了一些尝试以及修改pg fdw 源码，支持（目前还是有问题）
start transaction 问题
cratedb 对于transction 是不支持的，但是做了协议兼容（兼容的begin语法）所以有问题了
因为pg fdw 对于transction 使用了start 处理，解决方法（修改pg fdw 源码为begin）
docker 构建
FROM postgres:12.3 as build
LABEL AUTHOR="dalongrong"
ENV TZ=Asia/Shanghai \
LANG=zh_CN.UTF-8
RUN set -x \
&& ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone \
&& localedef -i zh_CN -c -f UTF-8 -A /usr/share/locale/locale.alias $LANG \
&& echo 'LANG="$LANG"' > /etc/default/locale \
&& apt-get update \
&& apt-get install -y --no-install-recommends patch ca-certificates wget unzip make postgresql-server-dev-"${PG_MAJOR}" gcc libc6-dev libssl-dev libkrb5-dev libaio1 gnupg \
&& wget -O /tmp/postgresql-12.3.tar.gz https:///pub/source/v12.3/postgresql-12.3.tar.gz \
&& wget -O /tmp/pg-fdw.patch https:///rongfengliang/pg-fdw-patch/main/pg-fdw.patch \
&& cd /tmp && tar xvzf postgresql-12.3.tar.gz \
&& cp /tmp/pg-fdw.patch /tmp/postgresql-12.3/contrib/postgres_fdw \
&& cd /tmp/postgresql-12.3/contrib/postgres_fdw \
&& patch -p0 connection.c pg-fdw.patch \
&& make USE_PGXS=1 install \
&& apt-get purge -y --auto-remove wget unzip make gnupg gcc postgresql-server-dev-"${PG_MAJOR}" libc6-dev libssl-dev libkrb5-dev \
&& apt-get autoremove \
&& apt-get autoclean \
&& rm -rf /var/lib/apt/lists/* \
&& rm -rf /tmp/*
FROM postgres:12.3
COPY --from=build /usr/lib/postgresql/12/lib/postgres_fdw.so /usr/lib/postgresql/12/lib/postgres_fdw.so
COPY --from=build /usr/lib/postgresql/12/lib/bitcode/postgres_fdw /usr/lib/postgresql/12/lib/bitcode/postgres_fdw
COPY --from=build /usr/share/postgresql/12/extension/postgres_fdw.control /usr/share/postgresql/12/extension/postgres_fdw.control
COPY --from=build /usr/share/postgresql/12/extension/postgres_fdw--1.0.sql /usr/share/postgresql/12/extension/postgres_fdw--1.0.sql
- 游标问题
此问题暂时无解，需要等待cratedb 对于游标的支持，主要的命令为DECLARE liahona CURSOR FOR SELECT * FROM films;
fdw 参考代码 
