This commit introduces AUTOVACUUM to Limbo. It introduces the concept of ptrmap pages and also adds some additional instructions that are required to make AUTOVACUUM PRAGMA work
The salts values in the WAL header are (re)generated in every checkpoint (but in PASSIVE mode), so if we find a frame with mismatch it means it's a leftover from a previous checkpoint.
Currently we are simply unable to read any WAL frames from disk
once a fresh process w/ Limbo is opened, since we never try to read
anything from disk unless we already have it in our in-memory
frame cache.
This commit implements a crude way of reading entire WAL into memory
as a single buffer and reconstructing the frame cache.
This PR adds `PRAGMA schema_version` to get the value of the schema-
version integer at offset 40 in the database header.
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#1427
WalShared state can be shared without having to wrap everything with a
lock, and instead use atomics on some places and rwlock on others -- for
now.
## Results:
From:
----
Execute `SELECT 1`/limbo_execute_select_1
time: [34.125 ns 34.218 ns 34.324 ns]
Execute `SELECT 1`/sqlite_execute_select_1
time: [28.124 ns 28.254 ns 28.385 ns]
To:
----
Gnuplot not found, using plotters backend
Execute `SELECT 1`/limbo_execute_select_1
time: [31.919 ns 32.113 ns 32.327 ns]
Execute `SELECT 1`/sqlite_execute_select_1
time: [29.662 ns 29.900 ns 30.139 ns]
We make read_record faster by not allocating Vec if not needed. This is
why I introduced a simple `SmallVec<T>` that will have a stack allocated
list for the simplest workloads, and a heap allocated if we were to
require more stuff.
Both read_varint and read_value, at least in my mac m4, were not
inlined. Since these functions are called so many times it made sense to
inline them to avoid call overhead. With this I saw something like 20%
improvement over previous commit in my m4.
