The commands module is modeled after backend/commands from the postgres repository and contains the logic for Citus on how to run these commands on distributed objects. Even though the structure of the directory has some resemblence to its postgres relative, files here are somewhat more fine-grained. This is due to the nature of citus commands that are heavily focused on distributed tables. Instead of having all commands in tablecmds.c they are often moved to files that are named after the command.

| File | Description | |------------------------------|-------------| | create_distributed_table.c | Implementation of UDF's for creating distributed tables | | drop_distributed_table.c | Implementation for dropping metadata for partitions of distributed tables | | extension.c | Implementation of CREATE EXTENSION commands for citus specific checks | | foreign_constraint.c | Implementation of and helper functions for foreign key constraints | | grant.c | Implementation of GRANT commands for roles/users on relations | | index.c | Implementation of commands specific to indices on distributed tables | | multi_copy.c | Implementation of COPY command. There are multiple different copy modes which are described in detail below | | policy.c | Implementation of CREATE\ALTER POLICY commands. | | rename.c | Implementation of ALTER ... RENAME ... commands. It implements the renaming of applicable objects, otherwise provides the user with a warning | | schema.c | | | sequence.c | Implementation of CREATE/ALTER SEQUENCE commands. Primarily checks correctness of sequence statements as they are not propagated to the worker nodes | | table.c | | | transmit.c | Implementation of COPY commands with format transmit set in the options. This format is used to transfer files from one node to another node | | truncate.c | Implementation of TRUNCATE commands on distributed tables | | utility_hook.c | This is the entry point from postgres into the commands module of citus. It contains the implementation that gets registered in postgres' ProcessUtility_hook callback to extends the functionality of the original ProcessUtility. This code is used to route the incoming commands to their respective implementation in Citus | | vacuum.c | Implementation of VACUUM commands on distributed tables |


The copy command is overloaded for a couple of use-cases specific to citus. The syntax of the command stays the same, however the implementation might slightly differ from the stock implementation. The overloading is mostly done via extra options that Citus uses to indicate how to operate the copy. The options used are described below.

FORMAT transmit

Implemented in transmit.c

TODO: to be written by someone with enough knowledge to write how, when and why it is used.

FORMAT result

Implemented in multi_copy.c

TODO: to be written by someone with enough knowledge to write how, when and why it is used.