These iterators (if you'd call them) provide safe abstractions over raw
pointers, enabling us to easily use them in the storage engine, reducing
verbosity and redundancy.
This has the ability to introduce UB because advancing the cursor might
invalidate the source pointers obtained by `protocol::Parser::parse()`
That's why we only forward the cursor after the query has been
executed. This is absolutely fine because even if another query
packet has been buffered, we will only forward by the amount we read
and not anything more.
This commit does an extreme amount of `unsafe` work to reduce the amount
of data that is copied around. Previously, we:
1. Copied in from the buffer
2. Copied again when we did a ptr::read
This changes that to:
1. Zero-copies for operations that can operate on borrowed values
(i.e values by ref like GET, KEYLEN, ..)
2. One copy for operations that need owned values
Overall, this may not immediately seem beneficial for small queries
(afterall, computer memory is very fast), but for large keys -- this can
make a very significant difference. However, a big difference can be noticed
in memory usage under heavy load (with as much as a tenfold drop in some
cases).
But to make this possible, we have to break free from Rust's borrowing
rules as we can't normally pass around refs easily. So, we just turn
everything into raw pointers and operate on them directly. This is why
we introduce a significant amount of unsafe code.
Where actions were supposed to report an action error, they silently ran
their significant part, ignoring the rest. This was fixed in:
- `DROP TABLE`
- `INSPECT KEYSPACES`
- `INSPECT KEYSPACE <ksid>`
- `INSPECT TABLE <entity>`
- `USE <entity>`
Tests for the same were added
When a new instance is created, we need to:
1. Create the tree
This ONLY creates the directories
2. Create the PRELOAD
This is critical because this is our check for a new instance
3. Flush the tables
This is important because we have never flushed the tables/ks before.
If we don't do this -- the server would fail to start with a
`directory not found` error.
Checking all encoding errors beforehand simplifies a lot of things for
us. At the same time, this saves a lot of bandwidth as we don't have to
write encoding errors for each element -- instead we just write one.
The create table query was being run with the workpool that also
attempts to switch to it on init (pre-loop stage). This caused us to
read in lesser bytes (since we use read_exact) and after the connection
is closed, the server would respond with a broken pipe error as it fails
to write data to the closed connection (since it expected to write more)
Sayan Nandan
Glydr