===dtm===Distributed transaction management tools for PostgreSQL.--------------------Communication scheme--------------------      .- Backend -.     /             \    /               \DTM ---- Backend ---- Coordinator    \               /     \             /      `- Backend -´-----------------------Coordinator-Backend API-----------------------This API includes a set of postgres procedures thatthe coordinator can call with "select" statement.extend_transaction (n integer) -> (higcid gcid)join_transaction (higcid gcid) -> ()FIXME: add procedures that would start and finish 2pc----------libdtm api----------typedef unsigned long long cid_t;// Connects to the specified DTM.DTMConn DtmConnect(char *host, int port);// Disconnects from the DTM. Do not use the 'dtm' pointer after this call, or// bad things will happen.void DtmDisconnect(DTMConn dtm);// Asks DTM for the first 'gcid' with unknown status. This 'gcid' is used as a// kind of snapshot. Returns the 'gcid' on success, or INVALID_GCID otherwise.cid_t DtmGlobalGetNextCid(DTMConn dtm);// Prepares a commit. Returns the 'gcid' on success, or INVALID_GCID otherwise.cid_t DtmGlobalPrepare(DTMConn dtm);// Finishes a given commit with 'committed' status. Returns 'true' on success,// 'false' otherwise.bool DtmGlobalCommit(DTMConn dtm, cid_t gcid);// Finishes a given commit with 'aborted' status.void DtmGlobalRollback(DTMConn dtm, cid_t gcid);// Gets the status of the commit identified by 'gcid'. Returns the status on// success, or -1 otherwise.int DtmGlobalGetTransStatus(DTMConn dtm, cid_t gcid);--------------------Backend-DTM Protocol--------------------DTM <--> Backend:<-   'p'<hex16 self> - "prepare"  -> '+'<hex16 gcid> - "commit prepared"  -> '-'             - "something went wrong"<-   'c'<hex16 gcid> - "commit"  -> '+'             - "commit saved"  -> '-'             - "something went wrong"<-   'a'<hex16 gcid> - "abort"  -> '+'             - "abort saved"  -> '-'             - "something went wrong"<-   'h'             - "horizon"  -> '+'<hex16 gcid> - "here is a gcid you can use as a snapshot"  -> '-'             - "something went wrong"<-   's'<hex16 gcid> - "status"  -> '+''c|a|?'      - "here is the transaction status"                       (c)ommitted, (a)borted or (?)unknown  -> '-'             - "something went wrong"Backend disconnection is considered as an abort of all incomplete commitsprepared by that backend.