diff --git a/applications/test/CompactListList/Test-CompactListList.C b/applications/test/CompactListList/Test-CompactListList.C
index 892fe58644..45d45e0996 100644
--- a/applications/test/CompactListList/Test-CompactListList.C
+++ b/applications/test/CompactListList/Test-CompactListList.C
@@ -171,7 +171,8 @@ int main(int argc, char *argv[])
             CompactListList<label>::pack(subfaces)
         );
         Info<< "compact faces:" << subCompact << endl;
-        Info<< "deserialized:" << subCompact.unpack() << endl;
+        Info<< "matrix content:" << nl;
+        subCompact.writeMatrix(Info) << endl;
     }
 
     return 0;
diff --git a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.C b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.C
index 484deb275d..4043af45e5 100644
--- a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.C
+++ b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2019-2022 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -144,34 +144,54 @@ Foam::CompactListList<T> Foam::CompactListList<T>::pack
 }
 
 
-// * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * * //
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
 template<class T>
-Foam::CompactListList<T>::CompactListList(const labelUList& listSizes)
+Foam::label Foam::CompactListList<T>::resize_offsets
+(
+    const labelUList& listSizes,
+    const bool checkOverflow
+)
 {
     const label len = listSizes.size();
+    label total = 0;
 
     if (len)
     {
         offsets_.resize(len+1);
 
-        label total = 0;
         for (label i = 0; i < len; ++i)
         {
             offsets_[i] = total;
             total += listSizes[i];
 
-#ifdef FULLDEBUG
-            if (total < offsets_[i])
+            if (checkOverflow && total < offsets_[i])
             {
                 reportOverflowAndExit(i, listSizes);
             }
-#endif
         }
 
         offsets_[len] = total;
-        values_.resize(total);
     }
+    else
+    {
+        clear();
+    }
+    return total;
+}
+
+
+// * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * * //
+
+template<class T>
+Foam::CompactListList<T>::CompactListList(const labelUList& listSizes)
+{
+    #ifdef FULLDEBUG
+    const label total = resize_offsets(listSizes, true);
+    #else
+    const label total = resize_offsets(listSizes, false);
+    #endif
+    values_.resize(total);
 }
 
 
@@ -182,29 +202,12 @@ Foam::CompactListList<T>::CompactListList
     const T& val
 )
 {
-    const label len = listSizes.size();
-
-    if (len)
-    {
-        offsets_.resize(len+1);
-
-        label total = 0;
-        for (label i = 0; i < len; ++i)
-        {
-            offsets_[i] = total;
-            total += listSizes[i];
-
-#ifdef FULLDEBUG
-            if (total < offsets_[i])
-            {
-                reportOverflowAndExit(i, listSizes);
-            }
-#endif
-        }
-
-        offsets_[len] = total;
-        values_.resize(total, val);
-    }
+    #ifdef FULLDEBUG
+    const label total = resize_offsets(listSizes, true);
+    #else
+    const label total = resize_offsets(listSizes, false);
+    #endif
+    values_.resize(total, val);
 }
 
 
@@ -282,32 +285,24 @@ Foam::CompactListList<T>::ranges() const
 template<class T>
 void Foam::CompactListList<T>::resize(const labelUList& listSizes)
 {
-    const label len = listSizes.size();
+    #ifdef FULLDEBUG
+    const label total = resize_offsets(listSizes, true);
+    #else
+    const label total = resize_offsets(listSizes, false);
+    #endif
+    values_.resize(total);
+}
 
-    if (len)
-    {
-        offsets_.resize(len+1);
 
-        label total = 0;
-        for (label i = 0; i < len; ++i)
-        {
-            offsets_[i] = total;
-            total += listSizes[i];
-#if 0
-            if (checkOverflow && total < offsets_[i])
-            {
-                reportOverflowAndExit(i, listSizes);
-            }
-#endif
-        }
-
-        offsets_[len] = total;
-        values_.resize(total);
-    }
-    else
-    {
-        clear();
-    }
+template<class T>
+void Foam::CompactListList<T>::resize_nocopy(const labelUList& listSizes)
+{
+    #ifdef FULLDEBUG
+    const label total = resize_offsets(listSizes, true);
+    #else
+    const label total = resize_offsets(listSizes, false);
+    #endif
+    values_.resize_nocopy(total);
 }
 
 
diff --git a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
index 91c68b103a..62b53ddb49 100644
--- a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
+++ b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListList.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2019-2022 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -98,11 +98,19 @@ class CompactListList
         );
 
         //- Avoid poorly sized offsets/values
-        void enforceSizeSanity();
+        inline void enforceSizeSanity();
 
         //- The max of localSizes, excluding the specified row
         label maxNonLocalSize(const label rowi) const;
 
+        //- Change the offset table based on the sizes
+        //- and return the total number of values to be stored but
+        //- does not touch the values array (unless the list is empty)
+        label resize_offsets
+        (
+            const labelUList& listSizes,
+            const bool checkOverflow = false
+        );
 
 public:
 
@@ -202,6 +210,9 @@ public:
         //- (for example).
         inline bool single() const noexcept;
 
+        //- The primary size (the number of rows/sublists)
+        inline label length() const noexcept;
+
         //- The primary size (the number of rows/sublists)
         inline label size() const noexcept;
 
@@ -299,6 +310,10 @@ public:
         //- Reset dimensions of CompactListList
         void resize(const labelUList& listSizes);
 
+        //- Reset dimensions of CompactListList
+        //- \em without preserving existing content
+        void resize_nocopy(const labelUList& listSizes);
+
         //- Alter local addressing size for given row, does not change content
         void setLocalSize(const label rowi, const label len);
 
@@ -390,6 +405,9 @@ public:
         inline const T& operator()(const label i, const label j) const;
 
 
+    // Iteration (FUTURE)
+
+
     // Reading/writing
 
         //- Read CompactListList as offsets/values pair from Istream,
@@ -399,6 +417,9 @@ public:
         //- Write CompactListList as offsets/values pair
         Ostream& writeList(Ostream& os, const label shortLen=0) const;
 
+        //- Write CompactListList as a formatted matrix of values (ASCII)
+        Ostream& writeMatrix(Ostream& os, const label shortLen=0) const;
+
 
     // IO Operators
 
diff --git a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListI.H b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListI.H
index 5a7733fb4c..969bc0d0af 100644
--- a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListI.H
+++ b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListI.H
@@ -183,9 +183,9 @@ inline std::streamsize Foam::CompactListList<T>::size_bytes() const noexcept
 template<class T>
 inline bool Foam::CompactListList<T>::empty() const noexcept
 {
-    // Note: could (should?) also check (offsets_.back() == 0)
-    // return offsets_.empty()
-    // || (*(offsets_.cdata() + offsets_.size()-1) == 0);
+    // Note: could (should?) also check total size??
+    // const label len = (offsets_.size() - 1);
+    // return (len < 1) || (*(offsets_.cdata() + len) == 0);
     return (offsets_.size() <= 1);
 }
 
@@ -197,6 +197,14 @@ inline bool Foam::CompactListList<T>::single() const noexcept
 }
 
 
+template<class T>
+inline Foam::label Foam::CompactListList<T>::length() const noexcept
+{
+    const label len = (offsets_.size() - 1);
+    return (len < 1) ? static_cast<label>(0) : len;
+}
+
+
 template<class T>
 inline Foam::label Foam::CompactListList<T>::size() const noexcept
 {
@@ -375,6 +383,7 @@ inline void Foam::CompactListList<T>::resize
 {
     offsets_.resize(mRows+1, Zero);
     values_.resize(nVals);
+    // Optionally: enforceSizeSanity();
 }
 
 
@@ -387,6 +396,7 @@ inline void Foam::CompactListList<T>::resize_nocopy
 {
     offsets_.resize(mRows+1, Zero);
     values_.resize_nocopy(nVals);
+    // Optionally: enforceSizeSanity();
 }
 
 
diff --git a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListIO.C b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListIO.C
index 07f5d25d37..8c3a96e596 100644
--- a/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListIO.C
+++ b/src/OpenFOAM/containers/CompactLists/CompactListList/CompactListListIO.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2022 OpenCFD Ltd.
+    Copyright (C) 2022-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -65,4 +65,34 @@ Foam::Ostream& Foam::CompactListList<T>::writeList
 }
 
 
+template<class T>
+Foam::Ostream& Foam::CompactListList<T>::writeMatrix
+(
+    Ostream& os,
+    const label shortLen
+) const
+{
+    const CompactListList<T>& mat = *this;
+
+    const auto oldFmt = os.format(IOstreamOption::ASCII);
+
+    // Write like multi-line matrix of rows (ASCII)
+    // TBD: with/without indenting?
+
+    const label nRows = mat.length();
+
+    os  << nRows << nl << token::BEGIN_LIST << nl;
+
+    for (label i = 0; i < nRows; ++i)
+    {
+        mat.localList(i).writeList(os, shortLen) << nl;
+    }
+
+    os  << token::END_LIST << nl;
+    os.format(oldFmt);
+
+    return os;
+}
+
+
 // ************************************************************************* //
diff --git a/src/OpenFOAM/parallel/globalIndex/globalIndex.H b/src/OpenFOAM/parallel/globalIndex/globalIndex.H
index a21fa0b156..6e37dfddf3 100644
--- a/src/OpenFOAM/parallel/globalIndex/globalIndex.H
+++ b/src/OpenFOAM/parallel/globalIndex/globalIndex.H
@@ -67,7 +67,7 @@ class globalIndex
 {
     // Private Data
 
-        //- Start of proci. Size is nProcs()+1. (so like CompactListList)
+        //- Offset (addressing) table - like CompactListList
         labelList offsets_;
 
 
@@ -182,7 +182,11 @@ public:
         //- Check for default constructed or total-size == 0
         inline bool empty() const noexcept;
 
+        //- The number of items covered by the offsets
+        inline label length() const noexcept;
+
         //- Global sum of localSizes. Same as totalSize()
+        FOAM_DEPRECATED_STRICT(2022-10, "totalSize() - less ambiguous")
         inline label size() const;
 
         //- The span size covered by the offsets, zero if empty
@@ -223,7 +227,8 @@ public:
         //- Such content is often created with gatherNone.
         inline bool single() const noexcept;
 
-        //- The number of processors covered by the offsets
+        //- The number of processors covered by the offsets,
+        //- same as the primary length()
         inline label nProcs() const noexcept;
 
         //- Range of process indices for all addressed offsets (processes)
@@ -353,6 +358,10 @@ public:
         //- Fatal for out of range ids (eg, negative or >= totalSize()
         inline label whichProcID(const label i) const;
 
+        //- Which processor does global id come from?
+        //- Checks proci first.
+        inline label whichProcID(const label proci, const label i) const;
+
 
     // Queries relating to myProcNo (Caution: uses UPstream::worldComm)
 
diff --git a/src/OpenFOAM/parallel/globalIndex/globalIndexI.H b/src/OpenFOAM/parallel/globalIndex/globalIndexI.H
index 4c3dfdd520..2a4da4716d 100644
--- a/src/OpenFOAM/parallel/globalIndex/globalIndexI.H
+++ b/src/OpenFOAM/parallel/globalIndex/globalIndexI.H
@@ -131,6 +131,19 @@ inline bool Foam::globalIndex::empty() const noexcept
 }
 
 
+inline bool Foam::globalIndex::single() const noexcept
+{
+    return (offsets_.size() == 2);
+}
+
+
+inline Foam::label Foam::globalIndex::length() const noexcept
+{
+    const label len = (offsets_.size() - 1);
+    return (len < 1) ? 0 : len;
+}
+
+
 inline Foam::label Foam::globalIndex::span() const noexcept
 {
     return (end_value() - begin_value());
@@ -168,16 +181,9 @@ inline Foam::labelList Foam::globalIndex::sizes() const
 }
 
 
-inline bool Foam::globalIndex::single() const noexcept
-{
-    return (offsets_.size() == 2);
-}
-
-
 inline Foam::label Foam::globalIndex::nProcs() const noexcept
 {
-    const label len = (offsets_.size() - 1);
-    return (len < 1) ? 0 : len;
+    return length();
 }
 
 
@@ -390,7 +396,11 @@ inline Foam::label Foam::globalIndex::toLocal(const label i) const
 }
 
 
-inline Foam::label Foam::globalIndex::whichProcID(const label i) const
+inline Foam::label Foam::globalIndex::whichProcID
+(
+    const label proci,
+    const label i
+) const
 {
     if (i < 0 || i >= totalSize())
     {
@@ -400,12 +410,19 @@ inline Foam::label Foam::globalIndex::whichProcID(const label i) const
             << abort(FatalError);
     }
 
-    const auto proci = UPstream::myProcNo(UPstream::worldComm);
-
     return isLocal(proci, i) ? proci : findLower(offsets_, i+1);
 }
 
 
+inline Foam::label Foam::globalIndex::whichProcID
+(
+    const label i
+) const
+{
+    return whichProcID(UPstream::myProcNo(UPstream::worldComm), i);
+}
+
+
 inline void Foam::globalIndex::reset
 (
     const globalIndex::gatherNone,
@@ -571,7 +588,7 @@ Foam::globalIndex::cbegin() const noexcept
 inline const Foam::globalIndex::const_iterator
 Foam::globalIndex::cend() const noexcept
 {
-    return const_iterator(this, this->nProcs());
+    return const_iterator(this, this->length());
 }
 
 
@@ -585,14 +602,14 @@ Foam::globalIndex::begin() const noexcept
 inline const Foam::globalIndex::const_iterator
 Foam::globalIndex::end() const noexcept
 {
-    return const_iterator(this, this->nProcs());
+    return const_iterator(this, this->length());
 }
 
 
 inline Foam::globalIndex::const_iterator
 Foam::globalIndex::cbegin(const label i) const noexcept
 {
-    const label len = this->nProcs();
+    const label len = this->length();
     return const_iterator(this, (i < 0 ? 0 : len < i ? len : i));
 }