ydb/yql/essentials/parser/pg_wrapper/readme.md

Directory postgresql/ contains PostgreSQL sources that were automatically patched to make all global variables to become thread-local ones. This makes it possible to use pg functions in multi-thread environment.

Also, there are some additional commits to postgresql/ (mostly backports from newer PostgreSQL versions or renames of PostgreSQL C functions when corresponding function is reimplemented outside of postgresql/ directory/)

Base version of PostgreSQL can be seen in copy_src.sh script (VERSION variable).

copy_src.sh script downloads, configures and builds static postgresql.a library from original PostgreSQL sources with minor patches (source.patch). After that, it finds all global r/w symbols by analyzing output of "objdump postgresql.a" command. Then it copies all necessary *.c and *.h files to postgresql/ directory, automatically changing all static variables to thread-local ones.

How to upgrade to newer PostgreSQL:

1. Make sure you have folloing packages installed (assuming you have Ubuntu Linux):

libicu-dev icu-devtools pkg-config liblz4-dev libreadline-dev libssl-dev libxml2-dev libossp-uuid-dev

1. On clean repository perform following command:

./copy_src.sh && git diff -R postgresql > local_changes.patch

In file local_changes.patch you will get all changes applied to postgresql/ directory which are not part of automated patching by copy_src.sh

1. Cleanup repositry:

git checkout .

1. Bump PostgreSQL version in copy_src.sh (it is recommended not to do big jumps here)

2. Run ./copy_src.sh

3. Assuming compilation and automatic patching were successful, apply local changes collected on step 2:

patch -p6 < local_changes.patch

Resolve possible conflicts. Usually, conflicts arise due to some already backported changes

1. Update pg_catalog data

(cd ../../tools/pg_catalog_dump/ && yag make --build=relwithdebinfo && ./pg_catalog_dump > dump.json)

1. Regenerate Arrow postgresql kernels

./generate_kernels.py

1. Make sure that resulting pg_wrapper library compiles and passes minimal tests

yag make --build=relwithdebinfo -tA -C ut -C test -C ../../sql/pg/ut

1. Verify that all global variables in PostgreSQL-originated sources are accounted for

./verify.sh

Should output OK

1. Submit PR (do not forget to git add all new files created in postgresql/ direcotry - they sshould also present in pg_sources.inc)