Previously done at Slot Level - but Blocks were still read from disk after the Slot CRC had been checked.
This seems safer. It requires an extra CRC check for every fetch. However, CRC chekcing smaller binaries during the buld process appears to be beneficial to performance.
Hoped this will be an enabler to turning off compression at Levels 0 and 1 to improve performance (wihtout having a compensating issues with reduced CRC performance)
Previouslythe tinybloom was used within the SST file as an extra check to remove false fetches.
However the SST already has a low FPR check in the slot_index. If the newebloom was used (which is no longer per slot, but per sst), this can be shared with the penciller and then the penciller could use it and avoid the message pass.
the message pass may be blocked by a 2i query or a slot fetch request for a merge. So this should make performance within the Penciller snappier.
This is as a result of taking sst_timings within a volume test - where there was an average of + 100microsecs for each level that was dropped down. Given the bloom/slot checks were < 20 microsecs - there seems to be some further delay.
The bloom is a binary of > 64 bytes - so passing it around should not require a copy.
Bloom filter that can take largere keys but is still efficient to build. Allows bloom filter to be checked without first detemrining the slot. Also, as represents the whole SST - it could be sent to the penciller to remove the need for a message pass.
The bloom is smaller and has a worse fpr than leveled_tinybloom. Failing the bloom check isn't so bad - due to the slot index check being relatively fast and having a very low fpr.
Producing the list of all slots to try appeared to be expensive. In volume tests taking 150 - 250 microseconds per GET. Perhaps the list could be long (>1000), with a split and append, so not surprising.
Instead loop and count.
Since High Sierra upgrade having a seperate line for platform_define 17 caused issues.
OTP 19 seemingly matched against it. OTP 18 had a redefine issue as it appeared to match against it as well.
Using this regex instead seems to work. Why? Why was htis not an issue before High Sierra?
