There is not guarantee or requirement for WAL writers to only add
series entries in increasing order of IDs. A postings list cannot look
back and thus unordered WAL entries would skip over IDs to not truncate
from the WAL.
We replace it with a simple boolean check function that does not require
order.
We were still fsyncing while holding the write lock when we cut a new
segment. Given we cannot do anything but logging errors, we might just
as well complete segments asynchronously.
There's not realistic use case where one would fsync after every WAL
entry, thus make the default of a flush interval of 0 to never fsync
which is a much more likely use case.
This adds various new locks to replace the single big lock on
the head. All parts now must be COW as they may be held by clients
after initial retrieval.
Series by ID and hashes are now held in a stripe lock to reduce
contention and total holding time during GC. This should reduce
starvation of readers.
This changes the structure to a single WAL backed by a single head
block.
Parts of the head block can be compacted. This relieves us from any head
amangement and greatly simplifies any consistency and isolation concerns
by just having a single head.
* Expose Stone as it is used in an exported method.
* Move from tombstoneReader to []Stone for the same reason as above.
* Make WAL reading a little cleaner.
Signed-off-by: Goutham Veeramachaneni <cs14btech11014@iith.ac.in>
This fixes different race condition encoutnered when running Prometheus.
It reduces the overall performance in the synthetic benchmark a fair bit
but has no indiciations of impacting a real-world setup notably.
This adds handling for various corruption scenarios of the WAL.
If corruption is encountered, we truncate the WAL after the last valid
entry transparently and continue appending after the offset.
This fixes a bug where the last WAL file was closed after consuming it
instead of being left open for further writes.
Reloading of blocks on startup considers loading head blocks now.
Introduce a seperate mutex for the head blocks to avoid a race where
a post-compaction reload may run between switching the DB's base mutex
to create a new head block in an appender.
File locks have a multitude of problems that make them hard to use
correctly. As they are just advisory, they are only meaningful to
prevent accidents like running the same process twice.
A simple PID file lock works reliably in those cases and is simpler.
The former approach created unordered postings list by either
map iteration of new series being unsorted (fixable) or concurrent
writers creating new series interleaved.
We switch back to generating ephemeral references for a single batch.
Newly created series have to be re-set upon the next insert.
