feat: add start-postgres-replica

Author: steve-chavez

README.md

@@ -86,6 +86,7 @@ The binary distributions have many extensions enabled; these include:
 - pg_tle
 - wrappers
 - supautils
+- citus
 
 You can just use `CREATE EXTENSION` to enable most of these. Some may require
 tweaks to [postgresql.conf](./tests/postgresql.conf) to enable.

docs/start-client-server.md

@@ -1,3 +1,5 @@
+## Running the server
+
 If you want to run a postgres server, just do this from the root of the
 repository:
 
@@ -18,7 +20,7 @@ valid "flake reference":
 nix run github:supabase/nix-postgres#start-server 14
 ```
 
-## Arbitrary versions at arbitrary git revisions
+### Arbitrary versions at arbitrary git revisions
 
 Let's say you want to use a PostgreSQL build from a specific version of the
 repository. You can change the syntax of the above to use _any_ version of the
@@ -39,3 +41,53 @@ nix run github:supabase/nix-postgres#start-server 14 &
 sleep 5
 nix run github:supabase/nix-postgres#start-client 15
 ```
+
+## Running a server replica
+
+To start a replica you can use the `start-postgres-replica` command.
+
+- first argument: the master version
+- second argument: the master port
+- third argument: the replica server port
+
+First start a server and a couple of replicas:
+
+```
+$ start-postgres-server 15 5435
+
+$ start-postgres-replica 15 5439
+
+$ start-postgres-replica 15 5440
+```
+
+Now check the master server:
+
+```
+$ start-postgres-client 15 5435
+```
+
+```sql
+SELECT client_addr, state
+FROM pg_stat_replication;
+ client_addr |   state
+-------------+-----------
+ ::1         | streaming
+ ::1         | streaming
+(2 rows)
+
+create table items as select x::int from generate_series(1,100) x;
+```
+
+And a replica:
+
+```
+$ start-postgres-client 15 5439
+```
+
+```sql
+select count(*) from items;
+ count
+-------
+   100
+(1 row)
+```

flake.nix

@@ -301,6 +301,15 @@
 
               chmod +x $out/bin/migrate-postgres
             '';
+
+          start-replica = pkgs.runCommand "start-postgres-replica" {} ''
+            mkdir -p $out/bin
+            substitute ${./tools/run-replica.sh.in} $out/bin/start-postgres-replica \
+              --subst-var-by 'PGSQL_SUPERUSER' '${pgsqlSuperuser}' \
+              --subst-var-by 'PSQL14_BINDIR' '${basePackages.psql_14.bin}' \
+              --subst-var-by 'PSQL15_BINDIR' '${basePackages.psql_15.bin}'
+            chmod +x $out/bin/start-postgres-replica
+          '';
         };
 
         # Create a testing harness for a PostgreSQL package. This is used for
@@ -361,6 +370,7 @@
           in {
           start-server = mkApp "start-server" "start-postgres-server";
           start-client = mkApp "start-client" "start-postgres-client";
+          start-replica = mkApp "start-replica" "start-postgres-replica";
           migration-test = mkApp "migrate-tool" "migrate-postgres";
         };
 
@@ -375,6 +385,7 @@
 
             basePackages.start-server
             basePackages.start-client
+            basePackages.start-replica
             basePackages.migrate-tool
           ];
           shellHook = ''

tests/postgresql.conf.in

@@ -199,7 +199,7 @@ dynamic_shared_memory_type = posix	# the default is the first option
 
 # - Settings -
 
-#wal_level = replica			# minimal, replica, or logical
+wal_level = logical			# minimal, replica, or logical
 					# (change requires restart)
 #fsync = on				# flush data to disk for crash safety
 					# (turning this off can cause
@@ -214,7 +214,7 @@ dynamic_shared_memory_type = posix	# the default is the first option
 					#   fsync_writethrough
 					#   open_sync
 #full_page_writes = on			# recover from partial page writes
-#wal_log_hints = off			# also do full page writes of non-critical updates
+wal_log_hints = on			# also do full page writes of non-critical updates
 					# (change requires restart)
 #wal_compression = off			# enable compression of full-page writes
 #wal_init_zero = on			# zero-fill new WAL files

tools/run-replica.sh.in

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+# shellcheck shell=bash
+
+[ ! -z "$DEBUG" ] && set -x
+
+# first argument should be '14' or '15' for the version
+if [ "$1" == "14" ]; then
+    echo "Starting server for PSQL 14"
+    PSQL14=@PSQL14_BINDIR@
+    BINDIR="$PSQL14"
+elif [ "$1" == "15" ]; then
+    echo "Starting server for PSQL 15"
+    PSQL15=@PSQL15_BINDIR@
+    BINDIR="$PSQL15"
+else
+    echo "Please provide a valid Postgres version (14 or 15)"
+    exit 1
+fi
+
+export PATH=$BINDIR/bin:$PATH
+
+PGSQL_SUPERUSER=@PGSQL_SUPERUSER@
+MASTER_PORTNO="$2"
+REPLICA_PORTNO="$3"
+REPLICA_SLOT="replica_$RANDOM"
+DATDIR=$(mktemp -d)
+mkdir -p "$DATDIR"
+
+echo "NOTE: runing pg_basebackup for server on port $MASTER_PORTNO"
+echo "NOTE: using replica slot $REPLICA_SLOT"
+
+pg_basebackup -p "$MASTER_PORTNO" -h localhost -U "${PGSQL_SUPERUSER}" -X stream -C -S "$REPLICA_SLOT" -v -R -D "$DATDIR"
+
+echo "NOTE: using port $REPLICA_PORTNO for replica"
+echo "NOTE: using temporary directory $DATDIR for data, which will not be removed"
+echo "NOTE: you are free to re-use this data directory at will"
+echo
+
+exec postgres -p "$REPLICA_PORTNO" -D "$DATDIR" -k /tmp

tools/run-server.sh.in

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+l!/usr/bin/env bash
 # shellcheck shell=bash
 
 [ ! -z "$DEBUG" ] && set -x