Include access/subtrans.h & access/commit_ts.h (#2147)

1. It's used to get detailed sub-transaction information for any
PostgreSQL transaction ID for a table.
2. Example : "subtrans_infos" example project

Author: isdaniel

Cargo.toml

@@ -50,6 +50,7 @@ exclude = [
     "pgrx-examples/triggers",
     "pgrx-examples/versioned_custom_libname_so",
     "pgrx-examples/versioned_so",
+    "pgrx-examples/subtrans_infos",
 ]
 
 [workspace.package]

pgrx-examples/subtrans_infos/.gitignore

@@ -0,0 +1,6 @@
+.DS_Store
+.idea/
+/target
+*.iml
+**/*.rs.bk
+Cargo.lock

pgrx-examples/subtrans_infos/Cargo.toml

@@ -0,0 +1,41 @@
+[package]
+name = "subtrans_infos"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[lib]
+crate-type = ["cdylib", "lib"]
+
+[[bin]]
+name = "pgrx_embed_subtrans_infos"
+path = "./src/bin/pgrx_embed.rs"
+
+[features]
+default = ["pg14"]
+pg13 = ["pgrx/pg13", "pgrx-tests/pg13"]
+pg14 = ["pgrx/pg14", "pgrx-tests/pg14"] 
+pg15 = ["pgrx/pg15", "pgrx-tests/pg15"]
+pg16 = ["pgrx/pg16", "pgrx-tests/pg16"]
+pg17 = ["pgrx/pg17", "pgrx-tests/pg17"]
+pg18 = ["pgrx/pg18", "pgrx-tests/pg18"]
+pg_test = []
+
+# Enable additional features for comprehensive testing
+testing = ["pg_test"]
+
+[dependencies]
+pgrx = { path = "../../pgrx", default-features = false }
+
+[dev-dependencies]
+pgrx-tests = { path = "../../pgrx-tests" }
+
+# uncomment these if compiling outside of 'pgrx'
+# [profile.dev]
+# panic = "unwind"
+
+# [profile.release]
+# panic = "unwind"
+# opt-level = 3
+# lto = "fat"
+# codegen-units = 1

pgrx-examples/subtrans_infos/README.md

@@ -0,0 +1,155 @@
+# subtrans_infos
+
+This extension allows you to get detailed subtransaction information for any PostgreSQL transaction ID, including:
+
+- Transaction status (in progress, committed, aborted)
+- Parent transaction ID
+- Top-level parent transaction ID  
+- Subtransaction nesting level
+- Commit timestamp (when available)
+
+The extension provides comprehensive safety checks and handles PostgreSQL's internal transaction management constraints properly.
+
+## Usage
+
+The extension provides a single function:
+
+```sql
+subtrans_infos(xid bigint) 
+RETURNS TABLE (
+    xid integer,
+    status text,
+    parent_xid integer,
+    top_parent_xid integer,
+    sub_level integer,
+    commit_timestamp timestamptz
+)
+```
+
+### Parameters
+
+- `xid`: The transaction ID to analyze (as a bigint)
+
+### Return Columns
+
+- `xid`: The input transaction ID (converted to integer)
+- `status`: Transaction status ("in progress", "committed", "aborted")
+- `parent_xid`: Direct parent transaction ID (NULL if top-level)
+- `top_parent_xid`: Top-level parent transaction ID (NULL if top-level or data unavailable)
+- `sub_level`: Subtransaction nesting level (NULL if top-level or data unavailable)
+- `commit_timestamp`: Timestamp when transaction was committed (NULL if not committed or unavailable)
+
+## Examples
+
+First, create a test table:
+
+```sql
+CREATE TABLE t1 (id int);
+```
+
+Start a transaction with savepoints:
+```sql
+BEGIN;
+INSERT INTO t1 VALUES(1); 
+SAVEPOINT a;
+INSERT INTO t1 VALUES(2); 
+SAVEPOINT b;
+INSERT INTO t1 VALUES(3);
+```
+
+Now analyze the transaction locks and subtransactions:
+```sql
+SELECT
+    pgl.pid,
+    pgl.locktype,
+    pgl.mode,
+    si.xid,
+    si.status AS "xid status",
+    si.parent_xid,
+    si.top_parent_xid,
+    si.sub_level,
+    si.commit_timestamp
+FROM (
+    SELECT *
+    FROM pg_locks
+    WHERE transactionid IS NOT NULL
+) pgl
+CROSS JOIN LATERAL subtrans_infos(pgl.transactionid::text::bigint) si
+ORDER BY si.xid;
+```
+
+Expected output (transaction IDs will vary):
+
+```
+  pid   |   locktype    |     mode      | xid  | xid status  | parent_xid | top_parent_xid | sub_level | commit_timestamp 
+--------+---------------+---------------+------+-------------+------------+----------------+-----------+------------------
+ 704841 | transactionid | ExclusiveLock | 1647 | in progress |            |                |           | 
+ 704841 | transactionid | ExclusiveLock | 1648 | in progress |       1647 |           1647 |         1 | 
+ 704841 | transactionid | ExclusiveLock | 1649 | in progress |       1648 |           1647 |         2 | 
+(3 rows)
+```
+
+Complete the transaction:
+```sql
+COMMIT;
+```
+
+### Example 2: Individual Transaction Analysis
+
+Query specific transaction IDs:
+```sql
+-- Check a specific transaction
+subtrans_infos=# SELECT * FROM subtrans_infos(1647);
+
+ xid  |  status   | parent_xid | top_parent_xid | sub_level |      commit_timestamp      
+------+-----------+------------+----------------+-----------+----------------------------
+ 1647 | committed |            |                |           | 2025-09-29 10:18:52.488217
+(1 row)
+```
+
+### Example 3: Analyzing Aborted Subtransactions
+
+```sql
+subtrans_infos=# BEGIN;
+INSERT INTO t1 VALUES(10);
+SAVEPOINT sp1;
+INSERT INTO t1 VALUES(20);
+SAVEPOINT sp2;
+INSERT INTO t1 VALUES(30);
+ROLLBACK TO SAVEPOINT sp1;  
+BEGIN
+INSERT 0 1
+SAVEPOINT
+INSERT 0 1
+SAVEPOINT
+INSERT 0 1
+ROLLBACK
+subtrans_infos=*# SELECT
+    si.xid,
+    si.status,
+    si.parent_xid,
+    si.top_parent_xid,
+    si.sub_level
+FROM pg_locks pgl
+CROSS JOIN LATERAL subtrans_infos(pgl.transactionid::text::bigint) si
+WHERE pgl.transactionid IS NOT NULL
+ORDER BY si.xid;
+ xid  |   status    | parent_xid | top_parent_xid | sub_level 
+------+-------------+------------+----------------+-----------
+ 1650 | in progress |            |                |          
+(1 row)
+
+
+subtrans_infos=*# SELECT * FROM subtrans_infos(1651);
+ xid  | status  | parent_xid | top_parent_xid | sub_level | commit_timestamp 
+------+---------+------------+----------------+-----------+------------------
+ 1651 | aborted |       1650 |           1650 |         1 | 
+(1 row)
+```
+
+## Remarks
+
+- `top_parent_xid` and `sub_level` may be NULL when subtransaction data is not available (e.g., for very old transactions)
+- Commit timestamps are only available when `track_commit_timestamp` is enabled
+- The extension properly handles PostgreSQL's transaction ID wraparound
+- All operations are safe and will not crash the database server

pgrx-examples/subtrans_infos/src/bin/pgrx_embed.rs

@@ -0,0 +1 @@
+::pgrx::pgrx_embed!();