Hi Henson,
> Attached is the v47 patches for Row pattern recognition (SQL/RPR).
> - Add src/backend/executor/README.rpr (previously was in ExecRPR.c)
README.rpr is extremely useful for those who want to review the RPR
patches. I found a room to enhance the document. Attached is a small
patch tries to enhance README.rpr, on top of v47.
- Make "target audience" and "scope" of the README more descriptive.
- Add References (currently the SQL standards only)
- Add explanation of some abbreviations (NFA, AST)
- Add reference sections for absorption. Readers might not be familiar with
"absorption"
- Add more fields to WindowAggState
- Add window framing rules with RPR
Regards,
--
Tatsuo Ishii
SRA OSS K.K.
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp
diff --git a/src/backend/executor/README.rpr b/src/backend/executor/README.rpr
index 52bcd77390c..dd98ce97adf 100644
--- a/src/backend/executor/README.rpr
+++ b/src/backend/executor/README.rpr
@@ -2,11 +2,15 @@
PostgreSQL Row Pattern Recognition: Flat-Array Stream NFA Guide
============================================================================
- Target audience: Developers with a basic understanding of the PostgreSQL
- executor and planner architecture
+ This README's target audience is developers with a basic
+ understanding of the PostgreSQL executor and planner architecture.
+ Also it would be better for them to understand the specification of
+ the row pattern recognition in the SQL standard [1][2]. If you do
+ not have access to the SQL standard, Oracle's manual or Trino's
+ manual can be alternatives for them.
- Scope: The entire process from PATTERN/DEFINE clause parsing to NFA
- runtime execution
+ This README's scope is the entire process from PATTERN/DEFINE clause
+ parsing to NFA runtime execution.
Related code:
- src/backend/parser/parse_rpr.c (parser phase)
@@ -23,10 +27,11 @@
What is a Flat-Array Stream NFA?
- The NFA in this implementation is not a traditional state-transition graph
- but a flat array of fixed-size 16-byte elements. At runtime, it processes
- the row stream in a forward-only manner, expanding epsilon transitions
- eagerly without backtracking.
+ The NFA (Nondeterministic Finite Automaton) in this implementation
+ is not a traditional state-transition graph but a flat array of
+ fixed-size 16-byte elements. At runtime, it processes the row stream
+ in a forward-only manner, expanding epsilon transitions eagerly
+ without backtracking.
- Flat-Array: Pattern compiled into a flat array,
not a graph (Chapter IV)
@@ -126,14 +131,14 @@ following:
(3) DEFINE clause transformation (transformDefineClause)
-III-2. PATTERN AST
+III-2. PATTERN AST (Abstract Syntax Tree)
The parser transforms the PATTERN clause into an RPRPatternNode tree.
Each node has one of the following four types:
RPR_PATTERN_VAR Variable reference. Name stored in varName field.
RPR_PATTERN_SEQ Concatenation. Children node list in children.
- RPR_PATTERN_ALT Alternation. Branch node list in children.
+ RPR_PATTERN_ALT Alternation (or). Branch node list in children.
RPR_PATTERN_GROUP Group (parentheses). Body node list in children.
All nodes have min/max fields to express quantifiers:
@@ -264,9 +269,11 @@ Element flags (1 byte, bitmask):
matches. (IV-4b)
0x04 RPR_ELEM_ABSORBABLE_BRANCH (VAR, BEGIN, END, ALT)
- Element lies within an absorbable region. Used at runtime
- to track whether the current NFA state is in an absorbable
- context.
+ Element lies within an absorbable region. Used at runtime to
+ track whether the current NFA state is in an absorbable
+ context. See "IV-5. Absorbability Analysis" and
+ "VIII-2. Solution: Context Absorption" for more details about
+ absorption.
0x08 RPR_ELEM_ABSORBABLE (VAR, END)
Absorption judgment point. Where to compare consecutive
@@ -508,7 +515,10 @@ V-3. RPR Fields of WindowAggState
nfaStateFree Reuse pool for states
nfaVarMatched Per-row cache: varMatched[varId]
nfaVisitedElems Bitmap for cycle detection
+ nfaVisitedNWords Number of bitmapwords in nfaVisitedElems
nfaStateSize Precomputed size of RPRNFAState
+ defineMatchStartDependent DEFINE vars needing per-context evaluation
(match_start-dependent)
+ nfaLastProcessedRow Last row processed by NFA (-1 = none)
Memory management:
@@ -1047,6 +1057,10 @@ X-3. INITIAL vs SEEK
X-4. Bounded Frame Handling
+ With RPR, the frame mode is always ROWS and the frame start must be
+ CURRENT ROW. The frame end can be either UNBOUNDED FOLLOWING or n
+ FOLLOWING.
+
When the frame is bounded (e.g., ROWS BETWEEN CURRENT ROW AND 5
FOLLOWING), ExecRPRProcessRow receives hasLimitedFrame=true and
frameOffset indicating the upper bound. Before the match phase,
@@ -1573,6 +1587,15 @@ C-7. PATTERN ((A+ B | C*)+ D) -- Per-branch absorption
in ALT
nullable.
BEGIN and ALT get ABSORBABLE_BRANCH (on the path to absorbable elements).
+
+References:
+
+[1] ISO/IEC 19075-5 Information technology - Guidance for the use of
+ database language SQL - Part 5: Row pattern recognition
+
+[2] ISO/IEC 9075-2 Information technology - Database languages - SQL -
+ Part 2: Foundation (SQL/Foundation)
+
============================================================================
End of document
============================================================================
