Even though Zabbix agent, Server and Proxy support metric data of at least a few MBs in size, the server truncates such values before writing those to the database.

Looking at the code, this is found in include/zbxdbhigh.h:

??#define ZBX_HISTORY_STR_VALUE_LEN 255
#define ZBX_HISTORY_TEXT_VALUE_LEN 65535
#define ZBX_HISTORY_LOG_VALUE_LEN 65535??

It is a reasonable limitation for MySQL/MariaDB that has 65535 bytes row size limit, however PostgreSQL can support more, which is useful when it comes to storing texts and logs.

Please implement a change that would raise those limits to at least a few MBs for PostgreSQL. Ideally the limit could be set via querying the database itself for it's limits.