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How can I get the default CF_handle by C API? #12316

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979357361 opened this issue Jan 31, 2024 · 2 comments · May be fixed by #12514
Open

How can I get the default CF_handle by C API? #12316

979357361 opened this issue Jan 31, 2024 · 2 comments · May be fixed by #12514

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@979357361
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I use RocksDB in C.
Now I need to multi_get a list of keys, there are two C API: rocksdb_multi_get and rocksdb_batched_multi_get_cf, notes tell that the later has performance improvement, but it need a cf arg<rocksdb_colume_family_handle_t> and this can not be NULL, as I only use the default cf, I can't find any API to get the default cf handle, more important, other C APIs I use are all no-cf arg, change them to cf-version is troublesome.

How can I get the CF_handle of default cf by C API? thanks!
@jowlyzhang
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In C++, there is a straightforward API DB::DefaultColumnFamily for this, but there is no counterpart API in C.

rocksdb/include/rocksdb/db.h

Line 1927 in 046ac91

virtual ColumnFamilyHandle* DefaultColumnFamily() const = 0;

A workaround would be to use this rocksdb_open_column_families API to open the DB

rocksdb/db/c.cc

Lines 915 to 919 in 046ac91

rocksdb_t* rocksdb_open_column_families(
const rocksdb_options_t* db_options, const char* name,
int num_column_families, const char* const* column_family_names,
const rocksdb_options_t* const* column_family_options,
rocksdb_column_family_handle_t** column_family_handles, char** errptr) {

Passing the column_family_handles output argument to get a handle for the default column family to keep for your own use.

@979357361
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Maybe we should add a C API to easy get the default CF_handle, as C API with "_cf" ending is hard to use and most time the default CF is enough, but "rocksdb_batched_multi_get_cf" must have it.

Later I will make a submit to add the C API, the code is straightforward.

@ajkr ajkr linked a pull request Apr 9, 2024 that will close this issue
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add c-api to get default cf handle 979357361/rocksdb
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@jowlyzhang @979357361