Summary:
This change has two primary goals (follow-up to https://github.com/facebook/rocksdb/issues/11917, https://github.com/facebook/rocksdb/issues/11920):
* Ensure the DB seqno_to_time_mapping has entries that allow us to put a good time lower bound on any writes that happen after setting up preserve/preclude options (either in a new DB, new CF, SetOptions, etc.) and haven't yet aged out of that time window. This allows us to remove a bunch of work-arounds in tests.
* For new DBs using preserve/preclude options, automatically reserve some sequence numbers and pre-map them to cover the time span back to the preserve/preclude cut-off time. In the future, this will allow us to import data from another DB by key, value, and write time by assigning an appropriate seqno in this DB for that write time.
Note that the pre-population (historical mappings) does not happen if the original options at DB Open time do not have preserve/preclude, so it is recommended to create initial column families at that time with create_missing_column_families, to take advantage of this (future) feature. (Adding these historical mappings after DB Open would risk non-monotonic seqno_to_time_mapping, which is dubious if not dangerous.)
Recommended follow-up:
* Solve existing race conditions (not memory safety) where parallel operations like CreateColumnFamily or SetDBOptions could leave the wrong setting in effect.
* Make SeqnoToTimeMapping more gracefully handle a possible case in which too many mappings are added for the time range of concern. It seems like there could be cases where data is massively excluded from the cold tier because of entries falling off the front of the mapping list (causing GetProximalSeqnoBeforeTime() to return 0). (More investigation needed.)
No release note for the minor bug fix because this is still an experimental feature with limited usage.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/11922
Test Plan: tests added / updated
Reviewed By: jowlyzhang
Differential Revision: D49956563
Pulled By: pdillinger
fbshipit-source-id: 92beb918c3a298fae9ca8e509717b1067caa1519
Summary:
This change is before a planned DBImpl change to ensure all sufficiently recent sequence numbers since Open are covered by SeqnoToTimeMapping (bug fix with existing test work-arounds). **Intended follow-up**
However, I found enough issues with SeqnoToTimeMapping to warrant this PR first, including very small fixes in DB implementation related to API contract of SeqnoToTimeMapping.
Functional fixes / changes:
* This fixes some mishandling of boundary cases. For example, if the user decides to stop writing to DB, the last written sequence number would perpetually have its write time updated to "now" and would always be ineligible for migration to cold tier. Part of the problem is that the SeqnoToTimeMapping would return a seqno known to have been written before (immediately or otherwise) the requested time, but compaction_job.cc would include that seqno in the preserve/exclude set. That is fixed (in part) by adding one in compaction_job.cc
* That problem was worse because a whole range of seqnos could be updated perpetually with new times in SeqnoToTimeMapping::Append (if no writes to DB). That logic was apparently optimized for GetOldestApproximateTime (now GetProximalTimeBeforeSeqno), which is not used in production, to the detriment of GetOldestSequenceNum (now GetProximalSeqnoBeforeTime), which is used in production. (Perhaps plans changed during development?) This is fixed in Append to optimize for accuracy of GetProximalSeqnoBeforeTime. (Unit tests added and updated.)
* Related: SeqnoToTimeMapping did not have a clear contract about the relationships between seqnos and times, just the idea of a rough correspondence. Now the class description makes it clear that the write time of each recorded seqno comes before or at the associated time, to support getting best results for GetProximalSeqnoBeforeTime. And this makes it easier to make clear the contract of each API function.
* Update `DBImpl::RecordSeqnoToTimeMapping()` to follow this ordering in gathering samples.
Some part of these changes has required an expanded test work-around for the problem (see intended follow-up above) that the DB does not immediately ensure recent seqnos are covered by its mapping. These work-arounds will be removed with that planned work.
An apparent compaction bug is revealed in
PrecludeLastLevelTest::RangeDelsCauseFileEndpointsToOverlap, so that test is disabled. Filed GitHub issue #11909
Cosmetic / code safety things (not exhaustive):
* Fix some confusing names.
* `seqno_time_mapping` was used inconsistently in places. Now just `seqno_to_time_mapping` to correspond to class name.
* Rename confusing `GetOldestSequenceNum` -> `GetProximalSeqnoBeforeTime` and `GetOldestApproximateTime` -> `GetProximalTimeBeforeSeqno`. Part of the motivation is that our times and seqnos here have the same underlying type, so we want to be clear about which is expected where to avoid mixing.
* Rename `kUnknownSeqnoTime` to `kUnknownTimeBeforeAll` because the value is a bad choice for unknown if we ever add ProximalAfterBlah functions.
* Arithmetic on SeqnoTimePair doesn't make sense except for delta encoding, so use better names / APIs with that in mind.
* (OMG) Don't allow direct comparison between SeqnoTimePair and SequenceNumber. (There is no checking that it isn't compared against time by accident.)
* A field name essentially matching the containing class name is a confusing pattern (`seqno_time_mapping_`).
* Wrap calls to confusing (but useful) upper_bound and lower_bound functions to have clearer names and more code reuse.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/11905
Test Plan: GetOldestSequenceNum (now GetProximalSeqnoBeforeTime) and TruncateOldEntries were lacking unit tests, despite both being used in production (experimental feature). Added those and expanded others.
Reviewed By: jowlyzhang
Differential Revision: D49755592
Pulled By: pdillinger
fbshipit-source-id: f72a3baac74d24b963c77e538bba89a7fc8dce51
Summary:
Add option `preserve_internal_time_seconds` to preserve the internal
time information.
It's mostly for the migration of the existing data to tiered storage (
`preclude_last_level_data_seconds`). When the tiering feature is just
enabled, the existing data won't have the time information to decide if
it's hot or cold. Enabling this feature will start collect and preserve
the time information for the new data.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10747
Reviewed By: siying
Differential Revision: D39910141
Pulled By: siying
fbshipit-source-id: 25c21638e37b1a7c44006f636b7d714fe7242138
Summary:
Using the Sequence number to time mapping to decide if a key is hot or not in
compaction and place it in the corresponding level.
Note: the feature is not complete, level compaction will run indefinitely until
all penultimate level data is cold and small enough to not trigger compaction.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10370
Test Plan:
CI
* Run basic db_bench for universal compaction manually
Reviewed By: siying
Differential Revision: D37892338
Pulled By: jay-zhuang
fbshipit-source-id: 792bbd91b1ccc2f62b5d14c53118434bcaac4bbe
Summary:
Which will be used for tiered storage to preclude hot data from
compacting to the cold tier (the last level).
Internally, adding seqno to time mapping. A periodic_task is scheduled
to record the current_seqno -> current_time in certain cadence. When
memtable flush, the mapping informaiton is stored in sstable property.
During compaction, the mapping information are merged and get the
approximate time of sequence number, which is used to determine if a key
is recently inserted or not and preclude it from the last level if it's
recently inserted (within the `preclude_last_level_data_seconds`).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10338
Test Plan: CI
Reviewed By: siying
Differential Revision: D37810187
Pulled By: jay-zhuang
fbshipit-source-id: 6953be7a18a99de8b1cb3b162d712f79c2b4899f
