Postgresql源码（86）varchar的创建与插入分析

/*
 *        varatt_expand_content
 *
 * Expand a varlena attribute to the specified number of bytes,
 * previously determined to be necessary.
 *
 * This must NOT be used on any datatype other than varlena.
 * It is okay to use on void* if the caller knows the actual datatype.
 */
static inline void
varatt_expand_content(bytea *varlena, Size newlen, bool *too_large)
{
    // 如果数据长度小于新长度，则扩展数据长度
    if (VARSIZE_ANY(varlena) < newlen)
    {
        // 如果新长度超出了最大存储长度，则设置too_large为true
        if (newlen > BYTEA_MAX_SIZE)
        {
            *too_large = true;
            return;
        }
        // 否则，设置too_large为false，并扩展数据长度
        *too_large = false;
        // 使用repalloc确保内存足够，并设置新的大小
        varlena = (bytea *) repalloc(varlena, newlen);
        // 设置新的大小
        SET_VARSIZE(varlena, newlen);
    }
}