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Clarify some DB::Open,OpenForReadOnly semantics (#8379)

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Summary:
Longstanding tech debt

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8379

Test Plan: Better than not having an API contract

Reviewed By: jay-zhuang

Differential Revision: D29011131

Pulled By: pdillinger

fbshipit-source-id: 2c4796177733651954024fc17875f8642ca08d09
This commit is contained in:
Peter Dillinger 2021-06-14 16:08:18 -07:00 committed by Facebook GitHub Bot
parent 3981430f54
commit 416dc7bed7
2 changed files with 20 additions and 4 deletions
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2
cache/cache_entry_roles.h vendored
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@ -27,7 +27,7 @@ enum class CacheEntryRole {
kIndexBlock, kIndexBlock,
// Other kinds of block-based table block // Other kinds of block-based table block
kOtherBlock, kOtherBlock,
// WriteBufferManager resevations to account for memtable usage // WriteBufferManager reservations to account for memtable usage
kWriteBuffer, kWriteBuffer,
// Default bucket, for miscellaneous cache entries. Do not use for // Default bucket, for miscellaneous cache entries. Do not use for
// entries that could potentially add up to large usage. // entries that could potentially add up to large usage.

22
include/rocksdb/db.h
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@ -140,11 +140,15 @@ typedef std::unordered_map<std::string, std::shared_ptr<const TableProperties>>
// and a number of wrapper implementations. // and a number of wrapper implementations.
class DB { class DB {
public: public:
// Open the database with the specified "name". // Open the database with the specified "name" for reads and writes.
// Stores a pointer to a heap-allocated database in *dbptr and returns // Stores a pointer to a heap-allocated database in *dbptr and returns
// OK on success. // OK on success.
// Stores nullptr in *dbptr and returns a non-OK status on error. // Stores nullptr in *dbptr and returns a non-OK status on error, including
// Caller should delete *dbptr when it is no longer needed. // if the DB is already open (read-write) by another DB object. (This
// guarantee depends on options.env->LockFile(), which might not provide
// this guarantee in a custom Env implementation.)
//
// Caller must delete *dbptr when it is no longer needed.
static Status Open(const Options& options, const std::string& name, static Status Open(const Options& options, const std::string& name,
DB** dbptr); DB** dbptr);
@ -153,6 +157,12 @@ class DB {
// If the db is opened in read only mode, then no compactions // If the db is opened in read only mode, then no compactions
// will happen. // will happen.
// //
// While a given DB can be simultaneously open via OpenForReadOnly
// by any number of readers, if a DB is simultaneously open by Open
// and OpenForReadOnly, the read-only instance has undefined behavior
// (though can often succeed if quickly closed) and the read-write
// instance is unaffected. See also OpenAsSecondary.
//
// Not supported in ROCKSDB_LITE, in which case the function will // Not supported in ROCKSDB_LITE, in which case the function will
// return Status::NotSupported. // return Status::NotSupported.
static Status OpenForReadOnly(const Options& options, const std::string& name, static Status OpenForReadOnly(const Options& options, const std::string& name,
@ -165,6 +175,12 @@ class DB {
// column family. The default column family name is 'default' and it's stored // column family. The default column family name is 'default' and it's stored
// in ROCKSDB_NAMESPACE::kDefaultColumnFamilyName // in ROCKSDB_NAMESPACE::kDefaultColumnFamilyName
// //
// While a given DB can be simultaneously open via OpenForReadOnly
// by any number of readers, if a DB is simultaneously open by Open
// and OpenForReadOnly, the read-only instance has undefined behavior
// (though can often succeed if quickly closed) and the read-write
// instance is unaffected. See also OpenAsSecondary.
//
// Not supported in ROCKSDB_LITE, in which case the function will // Not supported in ROCKSDB_LITE, in which case the function will
// return Status::NotSupported. // return Status::NotSupported.
static Status OpenForReadOnly( static Status OpenForReadOnly(