Performance[MQBSTAT]: lookup for per-appId metrics O(n) -> O(1)

[678098]

Previously, we used a bsl::list<ManagedPtr<mwcst::StatContext> > for 2 roles:

• Store managed pointers to subcontexts associated with appIds
• Lookup to subcontexts for each specific appId

The problem is that the list assumes linear search, which might be too slow if we have a decent number of appIds.

However, due to the interfaces of ManagedPtr (on Solaris), we cannot just use a container which might reallocate its elements on resize. So instead we keep&update 2 collections together: bsl::list to hold ManagedPointers and bsl::unordered_map for fast lookup to raw pointers to the needed StatContexts

Full list of changes:

• mqbstat::QueueStatsDomain: hold managed pointers in bsl::list<StatSubContextMp> d_subContextsHolder, lookup to subcontexts with bsl::unordered_map<bsl::string, mwcst::StatContext*> d_subContextsLookup
• mqbstat::QueueStatsDomain: pass allocator in constructor
• mqbstat::QueueStatsDomain: improve logging when no subcontext found
• mqbc::ClusterDataIdentity: add safety check to prevent possible nullptr dereference
• mqbmock::Cluster: add safety checks to find cluster misconfiguration early
• mqbstat_queuestats.t.cpp: add UT to check per-appId subcontexts and metrics

[kaikulimu]

However, due to the interfaces of ManagedPtr (on Solaris), we cannot just use a container which might reallocate its elements on resize.

Do you have source to this statement? It is quite inconvenient to have to use two data structures.

[678098]

Do you have source to this statement? It is quite inconvenient to have to use two data structures.

@kaikulimu ManagedPtr docs https://bloomberg.github.io/bde-resources/doxygen/bde_api_prod/bslma__managedptr_8h_source.html

However, like 'bsl::auto_ptr' it has unusual "copy-semantics" that transfer ownership of the managed object, rather than making a copy. It should be noted that this signature does not satisfy the requirements for an element-type stored in any of the standard library containers.

So ManagedPtr doesn't satisfy the CopyConstructible requirements https://en.cppreference.com/w/cpp/named_req/CopyConstructible

On SunOS, trying to build a bsl::unordered_map<bsl::string, bslma::ManagedPtr<...> > will cause compilation errors, so as with other container types which rely on reallocating its elements.

2024-08-07 13:57:33 | "/opt/bb/include/bslstl_pair.h", line 2528: Error: Could not find a match for BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>::ManagedPtr<MANAGED_TYPE>(const BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>) needed in void bsl::Pair_Second<BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>>::Pair_Second<BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>>(const BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>&, BloombergLP::bslma::Allocator*, bsl::integral_constant<int, 0>). 2024-08-07 13:57:33 | "/opt/bb/include/bslstl_pair.h", line 2792: Where: While instantiating "void bsl::Pair_Second<BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>>::Pair_Second<BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>>(const BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>&, BloombergLP::bslma::Allocator*, bsl::integral_constant<int, 0>)". 2024-08-07 13:57:33 | "/opt/bb/include/bslstl_pair.h", line 2792: Where: Instantiated from bsl::pair<const bsl::basic_string<char, std::char_traits<char>, bsl::allocator<char>>, BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>>::pair(const bsl::basic_string<char, std::char_traits<char>, bsl::allocator<char>>&, const BloombergLP::bslma::ManagedPtr<BloombergLP::mwcst::StatContext>&, BloombergLP::bslma::Allocator*). 2024-08-07 13:57:33 | "/opt/bb/include/bslma_constructionutil_cpp03.h", line 9370: Where: Instantiated from static void bsl::allocator_traits<bsl::allocator<long double>>::construct<bsl::pair<const bsl::basic_string<char, std::char_traits<char>, bsl::allocator<char>>,

The first message could be simplified: Error: Could not find a match for ManagedPtr<StatContext>::ManagedPtr<MANAGED_TYPE>(const ManagedPtr<StatContext>)

If you check the ManagedPtr interfaces, there are no constructors accepting other ManagedPtrs qualified as const https://bloomberg.github.io/bde-resources/doxygen/bde_api_prod/classbslma_1_1ManagedPtr.html