为每个活动会话指定存储当前执行命令的文本所保留的内存量，它们被用于pg_stat_activity.query域。 如果指定值时没有单位，则以字节为单位。默认值是 1024字节。这个参数只能在服务器启动时被设置。
Sets the truncation threshold of queries in pg_stat_activity (and pg_stat_statements). Increase it if you have really long queries which are being cut off, but there is significant extra memory usage for keeping longer queries.
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