scylladb

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Botond Dénes 519e167611 Merge 'replica/table: check memtable before discarding tombstone during read' from Lakshmi Narayanan Sreethar

On the read path, the compacting reader is applied only to the sstable
reader. This can cause an expired tombstone from an sstable to be purged
from the request before it has a chance to merge with deleted data in
the memtable leading to data resurrection.

Fix this by checking the memtables before deciding to purge tombstones
from the request on the read path. A tombstone will not be purged if a
key exists in any of the table's memtables with a minimum live timestamp
that is lower than the maximum purgeable timestamp.

Fixes #20916

`perf-simple-query` stats before and after this fix :

`build/Dev/scylla perf-simple-query --smp=1 --flush` :
```
// Before this Fix
// ---------------
94941.79 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59393 insns/op,   24029 cycles/op,        0 errors)
97551.14 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59376 insns/op,   23966 cycles/op,        0 errors)
96599.92 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59367 insns/op,   23998 cycles/op,        0 errors)
97774.91 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59370 insns/op,   23968 cycles/op,        0 errors)
97796.13 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59368 insns/op,   23947 cycles/op,        0 errors)

         throughput: mean=96932.78 standard-deviation=1215.71 median=97551.14 median-absolute-deviation=842.13 maximum=97796.13 minimum=94941.79
instructions_per_op: mean=59374.78 standard-deviation=10.78 median=59369.59 median-absolute-deviation=6.36 maximum=59393.12 minimum=59367.02
  cpu_cycles_per_op: mean=23981.67 standard-deviation=32.29 median=23967.76 median-absolute-deviation=16.33 maximum=24029.38 minimum=23947.19

// After this Fix
// --------------
95313.53 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59392 insns/op,   24058 cycles/op,        0 errors)
97311.48 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59375 insns/op,   24005 cycles/op,        0 errors)
98043.10 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59381 insns/op,   23941 cycles/op,        0 errors)
96750.31 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59396 insns/op,   24025 cycles/op,        0 errors)
93381.21 tps ( 71.1 allocs/op,   0.0 logallocs/op,  14.1 tasks/op,   59390 insns/op,   24097 cycles/op,        0 errors)

         throughput: mean=96159.93 standard-deviation=1847.88 median=96750.31 median-absolute-deviation=1151.55 maximum=98043.10 minimum=93381.21
instructions_per_op: mean=59386.60 standard-deviation=8.78 median=59389.55 median-absolute-deviation=6.02 maximum=59396.40 minimum=59374.73
  cpu_cycles_per_op: mean=24025.13 standard-deviation=58.39 median=24025.17 median-absolute-deviation=32.67 maximum=24096.66 minimum=23941.22
```

This PR fixes a regression introduced in ce96b472d3 and should be backported to older versions.

Closes scylladb/scylladb#20985

* github.com:scylladb/scylladb:
  topology-custom: add test to verify tombstone gc in read path
  replica/table: check memtable before discarding tombstone during read
  compaction_group: track maximum timestamp across all sstables

2024-10-23 10:28:00 +03:00

CMakeLists.txt

build: bring abseil submodule back

2024-05-05 23:31:09 +03:00

compaction_group.hh

compaction_group: track maximum timestamp across all sstables

2024-10-18 19:19:11 +05:30

data_dictionary_impl.hh

cql3: statements: change default tombstone_gc mode for tablets

2024-04-24 10:42:10 +02:00

database_fwd.hh

…