What is the recommended way to update partial substrings of existing records in
lmdb ?
I could not find a way that allows to transfer not the entire record, thus
wasting memory bandwidth, but only say overwrite a single byte within say a 1
mbyte record, is it acceptable/safe to modify :
mdb_put(offset, partial_len)
mdb_cursor_put(offset, partial_len)
...
if (F_ISSET(flags, MDB_RESERVE))
data->mv_data = olddata.mv_data;
else if (!(mc->mc_flags & C_SUB)) {
if(!offset && !partial_len)
memcpy(olddata.mv_data, data->mv_data,
data->mv_size);
else
memcpy((char*)olddata.mv_data+offset,
data->mv_data, partial_len);// allow partial update within existing record at
offset
}
else {
memcpy(NODEKEY(leaf), key->mv_data,
key->mv_size);
goto fix_parent;
}
...
further to that, is it possible to allow retrieving current record size, data
with MDB_RESERVE, and what should be done if anything in case one opts not to
write anything into the returned data
} else if ((data->mv_size == olddata.mv_size) || F_ISSET(flags,
MDB_RESERVE) )// allow retrieving current record size, data with MDB_RESERVE
{
/* same size, just replace it. Note that we could
* also reuse this node if the new data is smaller,
* but instead we opt to shrink the node in that case.
*/
if (F_ISSET(flags, MDB_RESERVE))
{
if (!data->mv_size)
*data = olddata;// allow retrieving
current size, data with MDB_RESERVE by querying with size 0
else
data->mv_data = olddata.mv_data;
}
