How the request size calc when pgxc start dn?

[yansheng836]

When I start the dn, It has a error

Starting datanode master dn001.
2025-01-08 07:22:04.350 GMT [27068,coord(0.0)] LOG:  skipping missing configuration file "/data/tbase/global/global_tbase.conf"
2025-01-08 07:22:04.350 GMT [27068,coord(0.0)] LOG:  skipping missing configuration file "/data/tbase/global/global_tbase.conf"
2025-01-08 15:22:04.354 CST [27068,coord(0.0)] LOG:  listening on IPv4 address "0.0.0.0", port 40004
2025-01-08 15:22:04.354 CST [27068,coord(0.0)] LOG:  listening on IPv6 address "::", port 40004
2025-01-08 15:22:04.360 CST [27068,coord(0.0)] LOG:  listening on Unix socket "/tmp/.s.PGSQL.40004"
2025-01-08 15:22:04.363 CST [27068,coord(0.0)] FATAL:  could not map anonymous shared memory: 无法分配内存
2025-01-08 15:22:04.363 CST [27068,coord(0.0)] HINT:  This error usually means that PostgreSQL's request for a shared memory segment exceeded available memory, swap space, or huge pages. To reduce the request size (currently 2495567072 bytes), reduce PostgreSQL's shared memory usage, perhaps by reducing shared_buffers or max_connections.
2025-01-08 15:22:04.363 CST [27068,coord(0.0)] LOG:  database system is shut down
pg_ctl: could not start server
Examine the log output.
Done.

I want to know how the request size (currently 2495567072 bytes) calc？

Or is there any way I can debug it(pgxc_ctl) with gdb?