Summary:
This patch clarifies and refactors the logic around tracked keys in transactions.
Closes https://github.com/facebook/rocksdb/pull/3140
Differential Revision: D6290258
Pulled By: maysamyabandeh
fbshipit-source-id: 03b50646264cbcc550813c060b180fc7451a55c1
Summary:
Add tests to ensure that WritePrepared and WriteCommitted policies are cross compatible when the db WAL is empty. This is important when the admin want to switch between the policies. In such case, before the switch the admin needs to empty the WAL by i) committing/rollbacking all the pending transactions, ii) FlushMemTables
Closes https://github.com/facebook/rocksdb/pull/3118
Differential Revision: D6227247
Pulled By: maysamyabandeh
fbshipit-source-id: bcde3d92c1e89cda3b9cfa69f6a20af5d8993db7
Summary:
If possible, use -march or -mcpu to get enable all features available on the local CPU or architecture. Only if this is impossible, we will manually set -msse4.2. It should be safe as there'll be a warning printed if `USE_SSE` is set and the provided flags are insufficient to support SSE4.2.
Closes https://github.com/facebook/rocksdb/pull/3156
Differential Revision: D6304703
Pulled By: ajkr
fbshipit-source-id: 030a53491263300cae7fafb429114d87acc828ef
Summary:
Add per-exe execution capability
Add fix parsing of groups/tests
Add timer test exclusion
Fix unit tests
Ifdef threadpool specific tests that do not pass on Vista threadpool.
Remove spurious outout from prefix_test so test case listing works
properly.
Fix not using standard test directories results in file creation errors
in sst_dump_test.
BlobDb fixes:
In C++ end() iterators can not be dereferenced. They are not valid.
When deleting blob_db_ set it to nullptr before any other code executes.
Not fixed:. On Windows you can not delete a file while it is open.
[ RUN ] BlobDBTest.ReadWhileGC
d:\dev\rocksdb\rocksdb\utilities\blob_db\blob_db_test.cc(75): error: DestroyBlobDB(dbname_, options, bdb_options)
IO error: Failed to delete: d:/mnt/db\testrocksdb-17444/blob_db_test/blob_dir/000001.blob: Permission denied
d:\dev\rocksdb\rocksdb\utilities\blob_db\blob_db_test.cc(75): error: DestroyBlobDB(dbname_, options, bdb_options)
IO error: Failed to delete: d:/mnt/db\testrocksdb-17444/blob_db_test/blob_dir/000001.blob: Permission denied
write_batch
Should not call front() if there is a chance the container is empty
Closes https://github.com/facebook/rocksdb/pull/3152
Differential Revision: D6293274
Pulled By: sagar0
fbshipit-source-id: 318c3717c22087fae13b18715dffb24565dbd956
Summary:
Add a simple policy for NVMe write time life hint
Closes https://github.com/facebook/rocksdb/pull/3095
Differential Revision: D6298030
Pulled By: shligit
fbshipit-source-id: 9a72a42e32e92193af11599eb71f0cf77448e24d
Summary:
The previous compression type selection caused unexpected behavior when the base level was also the bottommost level. The following sequence of events could happen:
- full compaction generates files with `bottommost_compression` type
- now base level is bottommost level since all files are in the same level
- any compaction causes files to be rewritten `compression_per_level` type since bottommost compression didn't apply to base level
I changed the code to make bottommost compression apply to base level.
Closes https://github.com/facebook/rocksdb/pull/3141
Differential Revision: D6264614
Pulled By: ajkr
fbshipit-source-id: d7aaa8675126896684154a1f2c9034d6214fde82
Summary:
A race condition will happen when:
* a user thread writes a value, but it hits the write stop condition because there are too many un-flushed memtables, while holding blob_db_impl.write_mutex_.
* Flush is triggered and call flush begin listener and try to acquire blob_db_impl.write_mutex_.
Fixing it.
Closes https://github.com/facebook/rocksdb/pull/3149
Differential Revision: D6279805
Pulled By: yiwu-arbug
fbshipit-source-id: 0e3c58afb78795ebe3360a2c69e05651e3908c40
Summary:
`compression` shadow the method name in `BlobFile`. Rename it.
Closes https://github.com/facebook/rocksdb/pull/3148
Differential Revision: D6274498
Pulled By: yiwu-arbug
fbshipit-source-id: 7d293596530998b23b6b8a8940f983f9b6343a98
Summary:
To fix the issue of failing to decompress existing value after reopen DB with a different compression settings.
Closes https://github.com/facebook/rocksdb/pull/3142
Differential Revision: D6267260
Pulled By: yiwu-arbug
fbshipit-source-id: c7cf7f3e33b0cd25520abf4771cdf9180cc02a5f
Summary:
- moved existing compression options to `InitializeOptionsGeneral` since they cannot be set through options file
- added flag for `zstd_max_train_bytes` which was recently introduced by #3057
Closes https://github.com/facebook/rocksdb/pull/3128
Differential Revision: D6240460
Pulled By: ajkr
fbshipit-source-id: 27dbebd86a55de237ba6a45cc79cff9214e82ebc
Summary:
Without this option, running the compact benchmark on a DB containing only bottommost files simply returned immediately.
Closes https://github.com/facebook/rocksdb/pull/3138
Differential Revision: D6256660
Pulled By: ajkr
fbshipit-source-id: e3b64543acd503d821066f4200daa201d4fb3a9d
Summary:
Adds two new counters:
`key_lock_wait_count` counts how many times a lock was blocked by another transaction and had to wait, instead of being granted the lock immediately.
`key_lock_wait_time` counts the time spent acquiring locks.
Closes https://github.com/facebook/rocksdb/pull/3107
Differential Revision: D6217332
Pulled By: lth
fbshipit-source-id: 55d4f46da5550c333e523263422fd61d6a46deb9
Summary:
After move assignment, we need to re-initialized the moved PinnableSlice.
Also update blob_db_impl.cc to not reuse the moved PinnableSlice since it is supposed to be in an undefined state after move.
Closes https://github.com/facebook/rocksdb/pull/3127
Differential Revision: D6238585
Pulled By: yiwu-arbug
fbshipit-source-id: bd99f2e37406c4f7de160c7dee6a2e8126bc224e
Summary:
While investigating the usage of `new_table_iterator_nanos` perf counter, I saw some code was wrapper around with unnecessary status check ... so removed it.
Closes https://github.com/facebook/rocksdb/pull/3120
Differential Revision: D6229181
Pulled By: sagar0
fbshipit-source-id: f8a44fe67f5a05df94553fdb233b21e54e88cc34
Summary:
util/concurrent_arena.h:
CID 1396145 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
2. uninit_member: Non-static class member free_begin_ is not initialized in this constructor nor in any functions that it calls.
94 Shard() : allocated_and_unused_(0) {}
util/dynamic_bloom.cc:
1. Condition hash_func == NULL, taking true branch.
CID 1322821 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
3. uninit_member: Non-static class member data_ is not initialized in this constructor nor in any functions that it calls.
47 hash_func_(hash_func == nullptr ? &BloomHash : hash_func) {}
48
util/file_reader_writer.h:
204 private:
205 AlignedBuffer buffer_;
member_not_init_in_gen_ctor: The compiler-generated constructor for this class does not initialize buffer_offset_.
206 uint64_t buffer_offset_;
CID 1418246 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
member_not_init_in_gen_ctor: The compiler-generated constructor for this class does not initialize buffer_len_.
207 size_t buffer_len_;
208};
util/thread_local.cc:
341#endif
CID 1322795 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
3. uninit_member: Non-static class member pthread_key_ is not initialized in this constructor nor in any functions that it calls.
342}
40struct ThreadData {
2. uninit_member: Non-static class member next is not initialized in this constructor nor in any functions that it calls.
CID 1400668 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
4. uninit_member: Non-static class member prev is not initialized in this constructor nor in any functions that it calls.
41 explicit ThreadData(ThreadLocalPtr::StaticMeta* _inst) : entries(), inst(_inst) {}
42 std::vector<Entry> entries;
1. member_decl: Class member declaration for next.
43 ThreadData* next;
3. member_decl: Class member declaration for prev.
44 ThreadData* prev;
45 ThreadLocalPtr::StaticMeta* inst;
46};
Closes https://github.com/facebook/rocksdb/pull/3123
Differential Revision: D6233566
Pulled By: sagar0
fbshipit-source-id: aa2068790ea69787a0035c0db39d59b0c25108db
Summary:
Fix unreleased snapshot at the end of the test.
Closes https://github.com/facebook/rocksdb/pull/3126
Differential Revision: D6232867
Pulled By: yiwu-arbug
fbshipit-source-id: 651ca3144fc573ea2ab0ab20f0a752fb4a101d26
Summary:
Instead of using samples directly, we now support passing the samples through zstd's dictionary generator when `CompressionOptions::zstd_max_train_bytes` is set to nonzero. If set to zero, we will use the samples directly as the dictionary -- same as before.
Note this is the first step of #2987, extracted into a separate PR per reviewer request.
Closes https://github.com/facebook/rocksdb/pull/3057
Differential Revision: D6116891
Pulled By: ajkr
fbshipit-source-id: 70ab13cc4c734fa02e554180eed0618b75255497
Summary:
Previously setting `write_buffer_size` with `SetOptions` would only apply to new memtables. An internal user wanted it to take effect immediately, instead of at an arbitrary future point, to prevent OOM.
This PR makes the memtable's size mutable, and makes `SetOptions()` mutate it. There is one case when we preserve the old behavior, which is when memtable prefix bloom filter is enabled and the user is increasing the memtable's capacity. That's because the prefix bloom filter's size is fixed and wouldn't work as well on a larger memtable.
Closes https://github.com/facebook/rocksdb/pull/3119
Differential Revision: D6228304
Pulled By: ajkr
fbshipit-source-id: e44bd9d10a5f8c9d8c464bf7436070bb3eafdfc9
Summary:
include/rocksdb/metadata.h:
struct ColumnFamilyMetaData {
CID 1322804 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
2. uninit_member: Non-static class member file_count is not initialized in this constructor nor in any functions that it calls.
struct SstFileMetaData {
2. uninit_member: Non-static class member size is not initialized in this constructor nor in any functions that it calls.
4. uninit_member: Non-static class member smallest_seqno is not initialized in this constructor nor in any functions that it calls.
6. uninit_member: Non-static class member largest_seqno is not initialized in this constructor nor in any functions that it calls.
8. uninit_member: Non-static class member num_reads_sampled is not initialized in this constructor nor in any functions that it calls.
CID 1322807 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
10. uninit_member: Non-static class member being_compacted is not initialized in this constructor nor in any functions that it calls.
include/rocksdb/sst_file_writer.h:
struct ExternalSstFileInfo {
2. uninit_member: Non-static class member sequence_number is not initialized in this constructor nor in any functions that it calls.
4. uninit_member: Non-static class member file_size is not initialized in this constructor nor in any functions that it calls.
6. uninit_member: Non-static class member num_entries is not initialized in this constructor nor in any functions that it calls.
CID 1351697 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
8. uninit_member: Non-static class member version is not initialized in this constructor nor in any functions that it calls.
31 ExternalSstFileInfo() {}
include/rocksdb/utilities/transaction.h:
explicit Transaction(const TransactionDB* db) {}
2. uninit_member: Non-static class member log_number_ is not initialized in this constructor nor in any functions that it calls.
CID 1396133 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
4. uninit_member: Non-static class member field txn_state_._M_i is not initialized in this constructor nor in any functions that it calls.
473 Transaction() {}
Closes https://github.com/facebook/rocksdb/pull/3100
Differential Revision: D6227651
Pulled By: sagar0
fbshipit-source-id: 5caa4a2cf9471d1f9c3c073f81473636e1f0aa14
Summary:
After adding expiration to blob index in #3066, we are now able to add a compaction filter to cleanup expired blob index entries.
Closes https://github.com/facebook/rocksdb/pull/3090
Differential Revision: D6183812
Pulled By: yiwu-arbug
fbshipit-source-id: 9cb03267a9702975290e758c9c176a2c03530b83
Summary:
This options was introduced in the C++ API in #1953 .
Closes https://github.com/facebook/rocksdb/pull/3064
Differential Revision: D6139010
Pulled By: sagar0
fbshipit-source-id: 164de11d539d174cf3afe7cd40e667049f44b0bc
Summary:
Blob db will keep blob file if data in the file is visible to an active snapshot. Before this patch it checks whether there is an active snapshot has sequence number greater than the earliest sequence in the file. This is problematic since we take snapshot on every read, if it keep having reads, old blob files will not be cleanup. Change to check if there is an active snapshot falls in the range of [earliest_sequence, obsolete_sequence) where obsolete sequence is
1. if data is relocated to another file by garbage collection, it is the latest sequence at the time garbage collection finish
2. otherwise, it is the latest sequence of the file
Closes https://github.com/facebook/rocksdb/pull/3087
Differential Revision: D6182519
Pulled By: yiwu-arbug
fbshipit-source-id: cdf4c35281f782eb2a9ad6a87b6727bbdff27a45
Summary:
Add an option to enable/disable auto garbage collection, where we keep counting how many keys have been evicted by either deletion or compaction and decide whether to garbage collect a blob file.
Default disable auto garbage collection for now since the whole logic is not fully tested and we plan to make major change to it.
Closes https://github.com/facebook/rocksdb/pull/3117
Differential Revision: D6224756
Pulled By: yiwu-arbug
fbshipit-source-id: cdf53bdccec96a4580a2b3a342110ad9e8864dfe
Summary:
The test intent to wait until key being overwritten until proceed with garbage collection. It failed to wait for `PutUntil` finally finish. Fixing it.
Closes https://github.com/facebook/rocksdb/pull/3116
Differential Revision: D6222833
Pulled By: yiwu-arbug
fbshipit-source-id: fa9b57a772b92a66cf250b44e7975c43f62f45c5
Summary:
Evict oldest blob file and put it in obsolete_files list when close to blob db size limit. The file will be delete when the `DeleteObsoleteFiles` background job runs next time.
For now I set `kEvictOldestFileAtSize` constant, which controls when to evict the oldest file, at 90%. It could be tweaked or made into an option if really needed; I didn't want to expose it as an option pre-maturely as there are already too many :) .
Closes https://github.com/facebook/rocksdb/pull/3094
Differential Revision: D6187340
Pulled By: sagar0
fbshipit-source-id: 687f8262101b9301bf964b94025a2fe9d8573421
Summary:
The num() might return cur_num as 0 and we are making sure that
cur_num will not be 0 down the path. The mult variable is being set to
100.0/cur_num which makes program crash when cur_num is 0.
Closes https://github.com/facebook/rocksdb/pull/3105
Differential Revision: D6222594
Pulled By: ajkr
fbshipit-source-id: 986154709897ff4dbbeb0e8aa81eb8c0b2a2db76
Summary:
This patch will remove the existing comments that declare partitioning indexes and filters as experimental.
Closes https://github.com/facebook/rocksdb/pull/3115
Differential Revision: D6222227
Pulled By: maysamyabandeh
fbshipit-source-id: 6179ec43b22c518494051b674d91c9e1b54d4ac0
Summary:
Move WritePreparedTxnDB from pessimistic_transaction_db.h to its own header, write_prepared_txn_db.h
Closes https://github.com/facebook/rocksdb/pull/3114
Differential Revision: D6220987
Pulled By: maysamyabandeh
fbshipit-source-id: 18893fb4fdc6b809fe117dabb544080f9b4a301b
Summary:
It's also defined in db/dbformat.cc per 7fe3b32896
Closes https://github.com/facebook/rocksdb/pull/3111
Differential Revision: D6219140
Pulled By: ajkr
fbshipit-source-id: 0f2b14e41457334a4665c6b7e3f42f1a060a0f35
Summary:
Implements ValidateSnapshot for WritePrepared txns and also adds a unit test to clarify the contract of this function.
Closes https://github.com/facebook/rocksdb/pull/3101
Differential Revision: D6199405
Pulled By: maysamyabandeh
fbshipit-source-id: ace509934c307ea5d26f4bbac5f836d7c80fd240
Summary:
The motivation for this PR is to add to RocksDB support for differential (incremental) snapshots, as snapshot of the DB changes between two points in time (one can think of it as diff between to sequence numbers, or the diff D which can be thought of as an SST file or just set of KVs that can be applied to sequence number S1 to get the database to the state at sequence number S2).
This feature would be useful for various distributed storages layers built on top of RocksDB, as it should help reduce resources (time and network bandwidth) needed to recover and rebuilt DB instances as replicas in the context of distributed storages.
From the API standpoint that would like client app requesting iterator between (start seqnum) and current DB state, and reading the "diff".
This is a very draft PR for initial review in the discussion on the approach, i'm going to rework some parts and keep updating the PR.
For now, what's done here according to initial discussions:
Preserving deletes:
- We want to be able to optionally preserve recent deletes for some defined period of time, so that if a delete came in recently and might need to be included in the next incremental snapshot it would't get dropped by a compaction. This is done by adding new param to Options (preserve deletes flag) and new variable to DB Impl where we keep track of the sequence number after which we don't want to drop tombstones, even if they are otherwise eligible for deletion.
- I also added a new API call for clients to be able to advance this cutoff seqnum after which we drop deletes; i assume it's more flexible to let clients control this, since otherwise we'd need to keep some kind of timestamp < -- > seqnum mapping inside the DB, which sounds messy and painful to support. Clients could make use of it by periodically calling GetLatestSequenceNumber(), noting the timestamp, doing some calculation and figuring out by how much we need to advance the cutoff seqnum.
- Compaction codepath in compaction_iterator.cc has been modified to avoid dropping tombstones with seqnum > cutoff seqnum.
Iterator changes:
- couple params added to ReadOptions, to optionally allow client to request internal keys instead of user keys (so that client can get the latest value of a key, be it delete marker or a put), as well as min timestamp and min seqnum.
TableCache changes:
- I modified table_cache code to be able to quickly exclude SST files from iterators heep if creation_time on the file is less then iter_start_ts as passed in ReadOptions. That would help a lot in some DB settings (like reading very recent data only or using FIFO compactions), but not so much for universal compaction with more or less long iterator time span.
What's left:
- Still looking at how to best plug that inside DBIter codepath. So far it seems that FindNextUserKeyInternal only parses values as UserKeys, and iter->key() call generally returns user key. Can we add new API to DBIter as internal_key(), and modify this internal method to optionally set saved_key_ to point to the full internal key? I don't need to store actual seqnum there, but I do need to store type.
Closes https://github.com/facebook/rocksdb/pull/2999
Differential Revision: D6175602
Pulled By: mikhail-antonov
fbshipit-source-id: c779a6696ee2d574d86c69cec866a3ae095aa900
Summary:
GetCommitTimeWriteBatch is currently used to store some state as part of commit in 2PC. In MyRocks it is specifically used to store some data that would be needed only during recovery. So it is not need to be stored in memtable right after each commit.
This patch enables an optimization to write the GetCommitTimeWriteBatch only to the WAL. The batch will be written to memtable during recovery when the WAL is replayed. To cover the case when WAL is deleted after memtable flush, the batch is also buffered and written to memtable right before each memtable flush.
Closes https://github.com/facebook/rocksdb/pull/3071
Differential Revision: D6148023
Pulled By: maysamyabandeh
fbshipit-source-id: 2d09bae5565abe2017c0327421010d5c0d55eaa7
Summary:
The collapse of duplicate keys in write batch needs to sort the indexes of duplicate keys since it only checks the index in the batch with the head of the list of duplicate keys.
Closes https://github.com/facebook/rocksdb/pull/3093
Differential Revision: D6186800
Pulled By: maysamyabandeh
fbshipit-source-id: abc9ae8c2f1840445a5584f925cf86ecc6f37154
Summary:
* cleanup num_concurrent_simple_blobs. We don't do concurrent writes (by taking write_mutex_) so it doesn't make sense to have multiple non TTL files open. We can revisit later when we want to improve writes.
* cleanup eviction callback. we don't have plan to use it now.
* rename s/open_simple_blob_files_/open_non_ttl_file_/ and s/open_blob_files_/open_ttl_files_/ to avoid confusion.
Closes https://github.com/facebook/rocksdb/pull/3088
Differential Revision: D6182598
Pulled By: yiwu-arbug
fbshipit-source-id: 99e6f5e01fa66d31309cdb06ce48502464bac6ad
Summary:
There seems to be a typo mistake in env ReuseWritableFile func
where status is being returned twice.
Closes https://github.com/facebook/rocksdb/pull/3099
Differential Revision: D6196204
Pulled By: ajkr
fbshipit-source-id: abb6e3e1c1e772dd485fc39e7f1b9d502fa188fe
Summary:
- Release all snapshots before crashing and reopening the DB. Without this, we may attempt to release snapshots from an old DB using a new DB. That tripped an assertion.
- Release multiple snapshots in the same operation if needed. Without this, we would sometimes leak snapshots.
Closes https://github.com/facebook/rocksdb/pull/3098
Differential Revision: D6194923
Pulled By: ajkr
fbshipit-source-id: b9c89bcca7ebcbb6c7802c616f9d1175a005aadf
Summary:
The assertion was caught by `MySQLStyleTransactionTest/MySQLStyleTransactionTest.TransactionStressTest/5` when run in a loop. The caller doesn't track whether the released snapshot is oldest, so let this function handle that case.
Closes https://github.com/facebook/rocksdb/pull/3080
Differential Revision: D6185257
Pulled By: ajkr
fbshipit-source-id: 4b3015c11db5d31e46521a00af568546ef4558cd
Summary:
write_options.sync = true and write_options.disableWAL is incompatible. When WAL is disabled, we are not able to persist the write immediately. Return an error in this case to avoid misuse of the options.
Closes https://github.com/facebook/rocksdb/pull/3086
Differential Revision: D6176822
Pulled By: yiwu-arbug
fbshipit-source-id: 1eb10028c14fe7d7c13c8bc12c0ef659f75aa071
Summary:
Problem was in bottommost compaction, when an L0->L0 compaction happened and L0 was bottommost. Then we'd preserve tombstones according to `Compaction::KeyNotExistsBeyondOutputLevel`, while zeroing seqnum according to `CompactionIterator::PrepareOutput`, thus triggering the assertion in `PrepareOutput`. To fix, we can just drop tombstones in L0->L0 when the output is "bottommost", i.e., the compaction includes the oldest L0 file and there's nothing at lower levels.
Closes https://github.com/facebook/rocksdb/pull/3085
Differential Revision: D6175742
Pulled By: ajkr
fbshipit-source-id: 8ab19a2e001496f362e9eb0a71757e2f6ecfdb3b
Summary:
We don't propagate TableProperty::oldest_key_time on compaction and just write the default value to SST files. It is more natural to default the value to 0.
Also revert db_sst_test back to before #2842.
Closes https://github.com/facebook/rocksdb/pull/3079
Differential Revision: D6165702
Pulled By: yiwu-arbug
fbshipit-source-id: ca3ce5928d96ae79a5beb12bb7d8c640a71478a0
Summary:
SstFileManager move files that need to be deleted into a trash directory.
Deprecate this behaviour and instead add ".trash" extension to files that need to be deleted
Closes https://github.com/facebook/rocksdb/pull/2970
Differential Revision: D5976805
Pulled By: IslamAbdelRahman
fbshipit-source-id: 27374ece4315610b2792c30ffcd50232d4c9a343
Summary:
Changing blob file format and some code cleanup around the change. The change with blob log format are:
* Remove timestamp field in blob file header, blob file footer and blob records. The field is not being use and often confuse with expiration field.
* Blob file header now come with column family id, which always equal to default column family id. It leaves room for future support of column family.
* Compression field in blob file header now is a standalone byte (instead of compact encode with flags field)
* Blob file footer now come with its own crc.
* Key length now being uint64_t instead of uint32_t
* Blob CRC now checksum both key and value (instead of value only).
* Some reordering of the fields.
The list of cleanups:
* Better inline comments in blob_log_format.h
* rename ttlrange_t and snrange_t to ExpirationRange and SequenceRange respectively.
* simplify blob_db::Reader
* Move crc checking logic to inside blob_log_format.cc
Closes https://github.com/facebook/rocksdb/pull/3081
Differential Revision: D6171304
Pulled By: yiwu-arbug
fbshipit-source-id: e4373e0d39264441b7e2fbd0caba93ddd99ea2af
Maysam Yabandeh