I _think_ this stems from rqlite's use of `sqlite3_deserialize()`. When using this, the resulting memory database is limited by `SQLITE_CONFIG_MEMDB_MAXSIZE`, which is [documented as defaulting to 1073741824 bytes](https://www.sqlite.org/c3ref/c_config_covering_index_scan.html#sqliteconfigmemdbmaxsize)
You could try increasing that value to see if it solves the issue for this user.
For instance, running a 64-bit build of SQLite on a machine with 256gb of RAM, it's fairly easy to hit this limit:
```
$ sqlite3 test.db
SQLite version 3.36.0 2021-06-18 18:36:39
Enter ".help" for usage hints.
sqlite> create table a(x);
sqlite> create table b(x);
sqlite> insert into a values ('abcdefghijklmnopqrstuvwxyz');
sqlite> .exit
$ sqlite3 --deserialize test.db
SQLite version 3.36.0 2021-06-18 18:36:39
Enter ".help" for usage hints.
sqlite> .schema
CREATE TABLE a(x);
CREATE TABLE b(x);
sqlite> insert into aux1.b select x from aux1.a;insert into aux1.a select x from aux1.b;
Error: no such table: aux1.b
sqlite> insert into b select x from a;insert into a select x from b;
[ .. repeated command 16 times .. ]
sqlite> insert into b select x from a;insert into a select x from b;
Error: database or disk is full
sqlite>
```
SQLite errored out with around 1gb of RAM usage. If I use a memory database directly, SQLite will use much more memory as I repeat the doubling of these two tables.