From 2f198664fa4f0c4f33691886427850f257aa7ee3 Mon Sep 17 00:00:00 2001
From: Michael Hoennig <michael@hoennig.de>
Date: Tue, 27 Aug 2024 20:03:03 +0200
Subject: [PATCH] extract tx_history_txid() into a CTE-query

---
 sql/historization.sql | 50 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 38 insertions(+), 12 deletions(-)

diff --git a/sql/historization.sql b/sql/historization.sql
index af902a17..37c266e1 100644
--- a/sql/historization.sql
+++ b/sql/historization.sql
@@ -15,6 +15,30 @@ drop type if exists tx_operation;
 
 create type "tx_operation" as enum ('INSERT', 'UPDATE', 'DELETE', 'TRUNCATE');
 
+
+create or replace function tx_history_txid()
+    returns xid8 stable
+    language plpgsql as $$
+declare
+    historicalTxIdSetting text;
+    historicalTxId xid8;
+    historicalTimestamp timestamp;
+begin
+    select current_setting('hsadminng.tx_history_txid', true) into historicalTxIdSetting;
+    raise notice 'tx_history_txid(): historicalTxIdSetting=%', historicalTxIdSetting;
+    if historicalTxIdSetting is null or historicalTxIdSetting = '' then
+        select current_setting('hsadminng.tx_history_timestamp', true)::timestamp into historicalTimestamp;
+        raise notice 'tx_history_txid(): historicalTimestamp=%', historicalTimestamp;
+        select max(txc.txid) from tx_context txc where txc.txtimestamp <= historicalTimestamp into historicalTxId;
+        raise notice 'tx_history_txid(): historicalTxId=%', historicalTxId;
+    else
+        historicalTxId = historicalTxIdSetting::xid8;
+    end if;
+    return historicalTxId;
+end; $$;
+
+
+
 create or replace function tx_historicize_tf()
     returns trigger
     language plpgsql
@@ -97,6 +121,8 @@ begin
     createViewSQL = format(
             'CREATE OR REPLACE VIEW %1$s AS' ||
             '(' ||
+            -- make sure the function is only called once, not for every matching row in tx_context
+            '  WITH txh AS (SELECT tx_history_txid() AS txid) ' ||
             '  SELECT %2$s' ||
             '    FROM %3$s' ||
             '   WHERE alive = TRUE' ||
@@ -105,7 +131,7 @@ begin
             '             SELECT max(ex.version_id) AS history_id' ||
             '               FROM %3$s AS ex' ||
             '               JOIN tx_context as txc ON ex.txid = txc.txid' ||
-            '              WHERE txc.txid = current_setting(''hsadminng.tx_history_txid'', true)::xid8' ||
+            '              WHERE txc.txid <= (SELECT txid FROM txh)' ||
             '              GROUP BY uuid' ||
             '         )' ||
             ')',
@@ -126,8 +152,6 @@ end; $$;
 
 call tx_create_historicization('hs_hosting_asset'); -- FIXME: move to 7010-hosting-asset.sql
 
--- and expanded:
-
 -- ===========================================================================================
 
 
@@ -138,19 +162,21 @@ call defineContext('historization testing', null, 'superuser-alex@hostsharing.ne
 --                    'hs_booking_project#D-1000300-mihdefaultproject:ADMIN'); -- prod
 --                    'hs_booking_project#D-1000300-mimdefaultproject:ADMIN'); -- test
 -- update hs_hosting_asset set caption='lug00 b' where identifier = 'lug00' and type = 'MANAGED_WEBSPACE'; -- prod
-update hs_hosting_asset set caption='hsh00 E ' || now()::text where identifier = 'hsh00' and type = 'MANAGED_WEBSPACE'; -- test
-update hs_hosting_asset set caption='hsh00 F ' || now()::text where identifier = 'hsh00' and type = 'MANAGED_WEBSPACE'; -- test
+update hs_hosting_asset set caption='hsh00 C ' || now()::text where identifier = 'hsh00' and type = 'MANAGED_WEBSPACE'; -- test
+update hs_hosting_asset set caption='hsh00 D ' || now()::text where identifier = 'hsh00' and type = 'MANAGED_WEBSPACE'; -- test
 commit;
 
 -- single version at point in time
 -- set hsadminng.tx_history_txid to (select max(txid) from tx_context where txtimestamp<='2024-08-27 12:13:13.450821');
-SELECT set_config('hsadminng.tx_history_txid', (select max(txid)::Text from tx_context where txtimestamp<='2024-08-27 12:13:13.450821'), FALSE);
-select uuid, version, identifier, caption from hs_hosting_asset_hv p where identifier in ('hsh00');
+set hsadminng.tx_history_txid to '3249';
+--set hsadminng.tx_history_timestamp to '2024-08-27 17:52:07.755407';
+-- all versions
+select tx_history_txid(), txc.txtimestamp, txc.currentUser, txc.currentTask, haex.*
+    from hs_hosting_asset_ex haex
+             join tx_context txc on haex.txid=txc.txid
+    where haex.identifier in ('hsh00', 'mim00');
+
+select uuid, version, identifier, caption from hs_hosting_asset_hv p where identifier in ('hsh00', 'mim00');
 
 select pg_current_xact_id();
 
--- all versions
-select txc.txtimestamp, txc.currentUser, txc.currentTask, haex.*
-    from hs_hosting_asset_ex haex
-    join tx_context txc on haex.txid=txc.txid
-   where haex.identifier in ('hsh00');