Summary:
Fixing the failure in IteratorsConsistentViewExplicitSnapshot as shown in https://github.com/facebook/rocksdb/actions/runs/8825927545/job/24230854140?pr=12581
The failure was due to the timing of the `flush()` for the later Column Family in the loop. If the flush for the later CFs installs the new super version before getting the SV for the iterator, assertion succeeds, but if the order flips, SV will be obsolete and assertion can fail.
This PR simplifies the test in a way that we do only one `flush()` so that `SYNC_POINT` can guarantee the order of operations. For ImplicitSnapshot test, it now just triggers flush for the second CF after obtaining SV for the first CF. For the ExplicitSnapshot test, it now triggers atomic flush() for all CFs after obtaining SV for the first CF.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12582
Test Plan:
```
./db_iterator_test --gtest_filter="*IteratorsConsistentView*"
./multi_cf_iterator_test -- --gtest_filter="*ConsistentView*
```
Reviewed By: ajkr, jowlyzhang
Differential Revision: D56557234
Pulled By: jaykorean
fbshipit-source-id: 7aa2f6d0e12a915b6e16cd240389bcfb5b4a5b62
Summary:
As mentioned in https://github.com/facebook/rocksdb/issues/12561 and https://github.com/facebook/rocksdb/issues/12566 , `NewIterators()` API has not been providing consistent view of the db across multiple column families. This PR addresses it by utilizing `MultiCFSnapshot()` function which has been used for `MultiGet()` APIs. To be able to obtain the thread-local super version with ref, `sv_exclusive_access` parameter has been added to `MultiCFSnapshot()` so that we could call `GetReferencedSuperVersion()` or `GetAndRefSuperVersion()` depending on the param and support `Refresh()` API for MultiCfIterators
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12573
Test Plan:
**Unit Tests Added**
```
./db_iterator_test --gtest_filter="*IteratorsConsistentView*"
```
```
./multi_cf_iterator_test -- --gtest_filter="*ConsistentView*"
```
**Performance Check**
Setup
```
make -j64 release
TEST_TMPDIR=/dev/shm/db_bench ./db_bench -benchmarks="filluniquerandom" -key_size=32 -value_size=512 -num=10000000 -compression_type=none
```
Run
```
TEST_TMPDIR=/dev/shm/db_bench ./db_bench -use_existing_db=1 -benchmarks="multireadrandom" -cache_size=10485760000
```
Before the change
```
DB path: [/dev/shm/db_bench/dbbench]
multireadrandom : 6.374 micros/op 156892 ops/sec 6.374 seconds 1000000 operations; (0 of 1000000 found)
```
After the change
```
DB path: [/dev/shm/db_bench/dbbench]
multireadrandom : 6.265 micros/op 159627 ops/sec 6.265 seconds 1000000 operations; (0 of 1000000 found)
```
Reviewed By: jowlyzhang
Differential Revision: D56444066
Pulled By: jaykorean
fbshipit-source-id: 327ce73c072da30c221e18d4f3389f49115b8f99
Summary:
Thanks to how we are using `DBIter` as child iterators in MultiCfIterators (both `CoalescingIterator` and `AttributeGroupIterator`), we got the lower/upper bound feature for free. This PR simply adds unit test coverage to ensure that the lower/upper bounds are working as expected in the MultiCfIterators.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12548
Test Plan:
UnitTest Added
```
./multi_cf_iterator_test
```
Reviewed By: ltamasi
Differential Revision: D56197966
Pulled By: jaykorean
fbshipit-source-id: fa51cc70705dbc5efd836ac006a7c6a49d05707a
Summary:
Continuing from the previous MultiCfIterator Implementations - (https://github.com/facebook/rocksdb/issues/12422, https://github.com/facebook/rocksdb/issues/12480#12465), this PR completes the `AttributeGroupIterator` by implementing `AttributeGroupIteratorImpl::AddToAttributeGroups()`. While implementing the `AttributeGroupIterator`, we had to make some changes in `MultiCfIteratorImpl` and found an opportunity to improve `Coalesce()` in `CoalescingIterator`.
Lifting `UNDER CONSTRUCTION - DO NOT USE` comment by replacing it with `EXPERIMENTAL`
Here are some implementation details:
- `IteratorAttributeGroups` is introduced to avoid having to copy all `WideColumn` objects during iteration.
- `PopulateIterator()` no longer advances non-top iterators that have the same key as the top iterator in the heap.
- `AdvanceIterator()` needs to advance the non-top iterators when they have the same key as the top iterator in the heap.
- Instead of populating one by one, `PopulateIterator()` now collects all items with the same key and calls `populate_func(items)` at once.
- This allowed optimization in `Coalesce()` such that we no longer do K-1 rounds of 2-way merge, but do one K-way merge instead.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12534
Test Plan:
Uncommented the assertions in `verifyAttributeGroupIterator()`
```
./multi_cf_iterator_test
```
Reviewed By: ltamasi
Differential Revision: D56089019
Pulled By: jaykorean
fbshipit-source-id: 6b0b4247e221f69b40b147d41492008cc9b15054
Summary:
There are a couple of reasons to modify the current implementation of the MultiCfIterator, which implements the generic `Iterator` interface.
- The default behavior of `value()`/`columns()` returning data from different Column Families for different keys can be prone to errors, even though there might be valid use cases where users do not care about the origin of the value/columns.
- The `attribute_groups()` API, which is not yet implemented, will not be useful for a single-CF iterator.
In this PR, we are implementing the following changes:
- `IteratorBase` introduced, which includes all basic iterator functions except `value()` and `columns()`.
- `Iterator`, which now inherits from `IteratorBase`, includes `value()` and `columns()`.
- New public interface `AttributeGroupIterator` inherits from `IteratorBase` and additionally includes `attribute_groups()` (to be implemented).
- Renamed former `MultiCfIterator` to `CoalescingIterator` which inherits from `Iterator`
- Existing MultiCfIteratorTest has been split into two - `CoalescingIteratorTest` and `AttributeGroupIteratorTest`.
- Moved AttributeGroup related code from `wide_columns.h` to a new file, `attribute_groups.h`.
Some Implementation Details
- `MultiCfIteratorImpl` takes two functions - `populate_func` and `reset_func` and use them to populate `value_` and `columns_` in CoalescingIterator and `attribute_groups_` in AttributeGroupIterator. In CoalescingIterator, populate_func is `Coalesce()`, in AttributeGroupIterator populate_func is `AddToAttributeGroups()`. `reset_func` clears populated value_, columns_ and attribute_groups_ accordingly.
- `Coalesce()` merge sorts columns from multiple CFs when a key exists in more than on CFs. column that appears in later CF overwrites the prior ones.
For example, if CF1 has `"key_1" ==> {"col_1": "foo", "col_2", "baz"}` and CF2 has `"key_1" ==> {"col_2": "quux", "col_3", "bla"}`, and when the iterator is at `key_1`, `columns()` will return `{"col_1": "foo", "col_2", "quux", "col_3", "bla"}`
In this example, `value()` will be empty, because none of them have values for `kDefaultColumnName`
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12480
Test Plan:
## Unit Test
```
./multi_cf_iterator_test
```
## Performance Test
To make sure this change does not impact existing `Iterator` performance
**Build**
```
$> make -j64 release
```
**Setup**
```
$> TEST_TMPDIR=/dev/shm/db_bench ./db_bench -benchmarks="filluniquerandom" -key_size=32 -value_size=512 -num=1000000 -compression_type=none
```
**Run**
```
TEST_TMPDIR=/dev/shm/db_bench ./db_bench -use_existing_db=1 -benchmarks="newiterator,seekrandom" -cache_size=10485760000
```
**Before the change**
```
DB path: [/dev/shm/db_bench/dbbench]
newiterator : 0.519 micros/op 1927904 ops/sec 0.519 seconds 1000000 operations;
DB path: [/dev/shm/db_bench/dbbench]
seekrandom : 5.302 micros/op 188589 ops/sec 5.303 seconds 1000000 operations; (0 of 1000000 found)
```
**After the change**
```
DB path: [/dev/shm/db_bench/dbbench]
newiterator : 0.497 micros/op 2011012 ops/sec 0.497 seconds 1000000 operations;
DB path: [/dev/shm/db_bench/dbbench]
seekrandom : 5.252 micros/op 190405 ops/sec 5.252 seconds 1000000 operations; (0 of 1000000 found)
```
Reviewed By: ltamasi
Differential Revision: D55353909
Pulled By: jaykorean
fbshipit-source-id: 8d7786ffee09e022261ce34aa60e8633685e1946
Summary:
This PR continues https://github.com/facebook/rocksdb/issues/12153 by implementing the missing `Iterator` APIs - `Seek()`, `SeekForPrev()`, `SeekToLast()`, and `Prev`. A MaxHeap Implementation has been added to handle the reverse direction.
The current implementation does not include upper/lower bounds yet. These will be added in subsequent PRs. The API is still marked as under construction and will be lifted after being added to the stress test.
Please note that changing the iterator direction in the middle of iteration is expensive, as it requires seeking the element in each iterator again in the opposite direction and rebuilding the heap along the way. The first `Next()` after `SeekForPrev()` requires changing the direction under the current implementation. We may optimize this in later PRs.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12422
Test Plan: The `multi_cf_iterator_test` has been extended to cover the API implementations.
Reviewed By: pdillinger
Differential Revision: D54820754
Pulled By: jaykorean
fbshipit-source-id: 9eb741508df0f7bad598fb8e6bd5cdffc39e81d1
Summary:
This PR introduces a new implementation of `Iterator` via a new public API called `NewMultiCfIterator()`. The new API takes a vector of column family handles to build a cross-column-family iterator, which internally maintains multiple `DBIter`s as child iterators from a consistent database state. When a key exists in multiple column families, the iterator selects the value (and wide columns) from the first column family containing the key, following the order provided in the `column_families` parameter. Similar to the merging iterator, a min heap is used to iterate across the child iterators. Backward iteration and direction change functionalities will be implemented in future PRs.
The comparator used to compare keys across different column families will be derived from the iterator of the first column family specified in `column_families`. This comparator will be checked against the comparators from all other column families that the iterator will traverse. If there's a mismatch with any of the comparators, the initialization of the iterator will fail.
Please note that this PR is not enough for users to start using `MultiCfIterator`. The `MultiCfIterator` and related APIs are still marked as "**DO NOT USE - UNDER CONSTRUCTION**". This PR is just the first of many PRs that will follow soon.
This PR includes the following:
- Introduction and partial implementation of the `MultiCfIterator`, which implements the generic `Iterator` interface. The implementation includes the construction of the iterator, `SeekToFirst()`, `Next()`, `Valid()`, `key()`, `value()`, and `columns()`.
- Unit tests to verify iteration across multiple column families in two distinct scenarios: (1) keys are unique across all column families, and (2) the same keys exist in multiple column families.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12153
Reviewed By: pdillinger
Differential Revision: D52308697
Pulled By: jaykorean
fbshipit-source-id: b03e69f13b40af5a8f0598d0f43a0bec01ef8294
