Don't force it into RAM; let it use disk as needed. Do you have it in a table? Or only in XML?

There is probably a single LOAD DATA statement to convert that from XML to a table defined thus:

CREATE TABLE Operations (
    id INT NOT NULL AUTO_INCREMENT,
    cid TINYINT UNSIGNED NOT NULL,
    aid TINYINT UNSIGNED NOT NULL,
    PRIMARY KEY(id)
) ENGINE=InnoDB;

The table will probably be smaller than your 300MB. Let it spill to disk if it needs to. (You have very little control anyway.) How big can the ids be? I picked the smallest datatype, but that assumes the numbers are between 0 and 255. Pick a larger datatype if needed.

Then do

 SELECT COUNT(DISTINCT cid, aid)
     FROM Operations;

That seems to be "number of nodes with distinct value on attributes cId and aId", but it looks like the answer will be 2, namely [2,5] and [2,6]. If Info_id is relevant to the counting, please explain how. (That may necessitate including it in the LOAD DATA.

Don't force it into RAM; let it use disk as needed. Do you have it in a table? Or only in XML?

There is probably a single LOAD DATA statement to convert that from XML to a table defined thus:

CREATE TABLE Operations (
    id INT NOT NULL AUTO_INCREMENT,
    cid TINYINT UNSIGNED NOT NULL,
    aid TINYINT UNSIGNED NOT NULL,
    PRIMARY KEY(id)
) ENGINE=InnoDB;

The table will probably be smaller than your 300MB. Let it spill to disk if it needs to. (You have very little control anyway.) How big can the ids be? I picked the smallest datatype, but that assumes the numbers are between 0 and 255. Pick a larger datatype if needed.

Then do

 SELECT COUNT(DISTINCT cid, aid)
     FROM Operations;

That seems to be "number of nodes with distinct value on attributes cId and aId", but it looks like the answer will be 2, namely [2,5] and [2,6]. If Info_id is relevant to the counting, please explain how. (That may necessitate including it in the LOAD DATA.

If you are exporting data from a spreadsheet,... Well, I see XML as an awful way to do it. Using a CSV file is easier and faster as an RDBMS-friendly format. After that, 3 SQL statements achieve the goal: CREATE TABLE, LOAD DATA, SELECT.