481 lines
17 KiB
Markdown
481 lines
17 KiB
Markdown
# Upgrading PostgreSQL Using Slony
|
|
|
|
This guide describes the steps one can take to upgrade their PostgreSQL database
|
|
to the latest version without the need for hours of downtime. This guide assumes
|
|
you have two database servers: one database server running an older version of
|
|
PostgreSQL (e.g. 9.2.18) and one server running a newer version (e.g. 9.6.0).
|
|
|
|
For this process we'll use a PostgreSQL replication tool called
|
|
["Slony"](https://www.slony.info/). Slony allows replication between different
|
|
PostgreSQL versions and as such can be used to upgrade a cluster with a minimal
|
|
amount of downtime.
|
|
|
|
In various places we'll refer to the user `gitlab-psql`. This user should be the
|
|
user used to run the various PostgreSQL OS processes. If you're using a
|
|
different user (e.g. `postgres`) you should replace `gitlab-psql` with the name
|
|
of said user. This guide also assumes your database is called
|
|
`gitlabhq_production`. If you happen to use a different database name you should
|
|
change this accordingly.
|
|
|
|
## Database Dumps
|
|
|
|
Slony only replicates data and not any schema changes. As a result we must
|
|
ensure that all databases have the same database structure.
|
|
|
|
To do so we'll generate a dump of our current database. This dump will only
|
|
contain the structure, not any data. To generate this dump run the following
|
|
command on your active database server:
|
|
|
|
```shell
|
|
sudo -u gitlab-psql /opt/gitlab/embedded/bin/pg_dump -h /var/opt/gitlab/postgresql -p 5432 -U gitlab-psql -s -f /tmp/structure.sql gitlabhq_production
|
|
```
|
|
|
|
If you're not using GitLab's Omnibus package you may have to adjust the paths to
|
|
`pg_dump` and the PostgreSQL installation directory to match the paths of your
|
|
configuration.
|
|
|
|
Once the structure dump is generated we also need to generate a dump for the
|
|
`schema_migrations` table. This table doesn't have any primary keys and as such
|
|
can't be replicated easily by Slony. To generate this dump run the following
|
|
command on your active database server:
|
|
|
|
```shell
|
|
sudo -u gitlab-psql /opt/gitlab/embedded/bin/pg_dump -h /var/opt/gitlab/postgresql/ -p 5432 -U gitlab-psql -a -t schema_migrations -f /tmp/migrations.sql gitlabhq_production
|
|
```
|
|
|
|
Next we'll need to move these files somewhere accessible by the new database
|
|
server. The easiest way is to simply download these files to your local system:
|
|
|
|
```shell
|
|
scp your-user@production-database-host:/tmp/*.sql /tmp
|
|
```
|
|
|
|
This will copy all the SQL files located in `/tmp` to your local system's
|
|
`/tmp` directory. Once copied you can safely remove the files from the database
|
|
server.
|
|
|
|
## Installing Slony
|
|
|
|
Slony will be used to upgrade the database without requiring long downtimes.
|
|
Slony can be downloaded from <https://www.slony.info/>. If you have installed
|
|
PostgreSQL using your operating system's package manager you may also be able to
|
|
install Slony using said package manager.
|
|
|
|
When compiling Slony from source you *must* use the following commands to do so:
|
|
|
|
```shell
|
|
./configure --prefix=/path/to/installation/directory --with-perltools --with-pgconfigdir=/path/to/directory/containing/pg_config/bin
|
|
make
|
|
make install
|
|
```
|
|
|
|
Omnibus users can use the following commands:
|
|
|
|
```shell
|
|
./configure --prefix=/opt/gitlab/embedded --with-perltools --with-pgconfigdir=/opt/gitlab/embedded/bin
|
|
make
|
|
make install
|
|
```
|
|
|
|
This assumes you have installed GitLab into `/opt/gitlab`.
|
|
|
|
To test if Slony is installed properly, run the following commands:
|
|
|
|
```shell
|
|
test -f /opt/gitlab/embedded/bin/slonik && echo 'Slony installed' || echo 'Slony not installed'
|
|
test -f /opt/gitlab/embedded/bin/slonik_init_cluster && echo 'Slony Perl tools are available' || echo 'Slony Perl tools are not available'
|
|
/opt/gitlab/embedded/bin/slonik -v
|
|
```
|
|
|
|
This assumes Slony was installed to `/opt/gitlab/embedded`. If Slony was
|
|
installed properly the output of these commands will be (the mentioned "slonik"
|
|
version may be different):
|
|
|
|
```plaintext
|
|
Slony installed
|
|
Slony Perl tools are available
|
|
slonik version 2.2.5
|
|
```
|
|
|
|
## Slony User
|
|
|
|
Next we must set up a PostgreSQL user that Slony can use to replicate your
|
|
database. To do so, log in to your production database using `psql` using a
|
|
super user account. Once done run the following SQL queries:
|
|
|
|
```sql
|
|
CREATE ROLE slony WITH SUPERUSER LOGIN REPLICATION ENCRYPTED PASSWORD 'password string here';
|
|
ALTER ROLE slony SET statement_timeout TO 0;
|
|
```
|
|
|
|
Make sure you replace "password string here" with the actual password for the
|
|
user. A password is *required*. This user must be created on _both_ the old and
|
|
new database server using the same password.
|
|
|
|
Once the user has been created make sure you note down the password as we will
|
|
need it later on.
|
|
|
|
## Configuring Slony
|
|
|
|
Now we can finally start configuring Slony. Slony uses a configuration file for
|
|
most of the work so we'll need to set this one up. This configuration file
|
|
specifies where to put log files, how Slony should connect to the databases,
|
|
etc.
|
|
|
|
First we'll need to create some required directories and set the correct
|
|
permissions. To do so, run the following commands on both the old and new
|
|
database server:
|
|
|
|
```shell
|
|
sudo mkdir -p /var/log/gitlab/slony /var/run/slony1 /var/opt/gitlab/postgresql/slony
|
|
sudo chown gitlab-psql:root /var/log/gitlab/slony /var/run/slony1 /var/opt/gitlab/postgresql/slony
|
|
```
|
|
|
|
Here `gitlab-psql` is the user used to run the PostgreSQL database processes. If
|
|
you're using a different user you should replace this with the name of said
|
|
user.
|
|
|
|
Now that the directories are in place we can create the configuration file. For
|
|
this we can use the following template:
|
|
|
|
```perl
|
|
if ($ENV{"SLONYNODES"}) {
|
|
require $ENV{"SLONYNODES"};
|
|
} else {
|
|
$CLUSTER_NAME = 'slony_replication';
|
|
$LOGDIR = '/var/log/gitlab/slony';
|
|
$MASTERNODE = 1;
|
|
$DEBUGLEVEL = 2;
|
|
|
|
add_node(host => 'OLD_HOST', dbname => 'gitlabhq_production', port =>5432,
|
|
user=>'slony', password=>'SLONY_PASSWORD', node=>1);
|
|
|
|
add_node(host => 'NEW_HOST', dbname => 'gitlabhq_production', port =>5432,
|
|
user=>'slony', password=>'SLONY_PASSWORD', node=>2, parent=>1 );
|
|
}
|
|
|
|
$SLONY_SETS = {
|
|
"set1" => {
|
|
"set_id" => 1,
|
|
"table_id" => 1,
|
|
"sequence_id" => 1,
|
|
"pkeyedtables" => [
|
|
TABLES
|
|
],
|
|
},
|
|
};
|
|
|
|
if ($ENV{"SLONYSET"}) {
|
|
require $ENV{"SLONYSET"};
|
|
}
|
|
|
|
# Please do not add or change anything below this point.
|
|
1;
|
|
```
|
|
|
|
In this configuration file you should replace a few placeholders before you can
|
|
use it. The following placeholders should be replaced:
|
|
|
|
- `OLD_HOST`: the address of the old database server.
|
|
- `NEW_HOST`: the address of the new database server.
|
|
- `SLONY_PASSWORD`: the password of the Slony user created earlier.
|
|
- `TABLES`: the tables to replicate.
|
|
|
|
The list of tables to replicate can be generated by running the following
|
|
command on your old PostgreSQL database:
|
|
|
|
```shell
|
|
sudo gitlab-psql gitlabhq_production -c "select concat('\"', schemaname, '.', tablename, '\",') from pg_catalog.pg_tables where schemaname = 'public' and tableowner = 'gitlab' and tablename != 'schema_migrations' order by tablename asc;" -t
|
|
```
|
|
|
|
If you're not using Omnibus you should replace `gitlab-psql` with the
|
|
appropriate path to the `psql` executable.
|
|
|
|
The above command outputs a list of tables in a format that can be copy-pasted
|
|
directly into the above configuration file. Make sure to _replace_ `TABLES` with
|
|
this output, don't just append it below it. Once done you'll end up with
|
|
something like this:
|
|
|
|
```perl
|
|
"pkeyedtables" => [
|
|
"public.abuse_reports",
|
|
"public.appearances",
|
|
"public.application_settings",
|
|
... more rows here ...
|
|
]
|
|
```
|
|
|
|
Once you have the configuration file generated you must install it on both the
|
|
old and new database. To do so, place it in
|
|
`/var/opt/gitlab/postgresql/slony/slon_tools.conf` (for which we created the
|
|
directory earlier on).
|
|
|
|
Now that the configuration file is in place we can _finally_ start replicating
|
|
our database. First we must set up the schema in our new database. To do so make
|
|
sure that the SQL files we generated earlier can be found in the `/tmp`
|
|
directory of the new server. Once these files are in place start a `psql`
|
|
session on this server:
|
|
|
|
```shell
|
|
sudo gitlab-psql gitlabhq_production
|
|
```
|
|
|
|
Now run the following commands:
|
|
|
|
```plaintext
|
|
\i /tmp/structure.sql
|
|
\i /tmp/migrations.sql
|
|
```
|
|
|
|
To verify if the structure is in place close the session, start it again, then
|
|
run `\d`. If all went well you should see output along the lines of the
|
|
following:
|
|
|
|
```plaintext
|
|
List of relations
|
|
Schema | Name | Type | Owner
|
|
--------+---------------------------------------------+----------+-------------
|
|
public | abuse_reports | table | gitlab
|
|
public | abuse_reports_id_seq | sequence | gitlab
|
|
public | appearances | table | gitlab
|
|
public | appearances_id_seq | sequence | gitlab
|
|
public | application_settings | table | gitlab
|
|
public | application_settings_id_seq | sequence | gitlab
|
|
public | approvals | table | gitlab
|
|
... more rows here ...
|
|
```
|
|
|
|
Now we can initialize the required tables and what not that Slony will use for
|
|
its replication process. To do so, run the following on the old database:
|
|
|
|
```shell
|
|
sudo -u gitlab-psql /opt/gitlab/embedded/bin/slonik_init_cluster --conf /var/opt/gitlab/postgresql/slony/slon_tools.conf | /opt/gitlab/embedded/bin/slonik
|
|
```
|
|
|
|
If all went well this will produce something along the lines of:
|
|
|
|
```plaintext
|
|
<stdin>:10: Set up replication nodes
|
|
<stdin>:13: Next: configure paths for each node/origin
|
|
<stdin>:16: Replication nodes prepared
|
|
<stdin>:17: Please start a slon replication daemon for each node
|
|
```
|
|
|
|
Next we need to start a replication node on every server. To do so, run the
|
|
following on the old database:
|
|
|
|
```shell
|
|
sudo -u gitlab-psql /opt/gitlab/embedded/bin/slon_start 1 --conf /var/opt/gitlab/postgresql/slony/slon_tools.conf
|
|
```
|
|
|
|
If all went well this will produce output such as:
|
|
|
|
```plaintext
|
|
Invoke slon for node 1 - /opt/gitlab/embedded/bin/slon -p /var/run/slony1/slony_replication_node1.pid -s 1000 -d2 slony_replication 'host=192.168.0.7 dbname=gitlabhq_production user=slony port=5432 password=hieng8ezohHuCeiqu0leeghai4aeyahp' > /var/log/gitlab/slony/node1/gitlabhq_production-2016-10-06.log 2>&1 &
|
|
Slon successfully started for cluster slony_replication, node node1
|
|
PID [26740]
|
|
Start the watchdog process as well...
|
|
```
|
|
|
|
Next we need to run the following command on the _new_ database server:
|
|
|
|
```shell
|
|
sudo -u gitlab-psql /opt/gitlab/embedded/bin/slon_start 2 --conf /var/opt/gitlab/postgresql/slony/slon_tools.conf
|
|
```
|
|
|
|
This will produce similar output if all went well.
|
|
|
|
Next we need to tell the new database server what it should replicate. This can
|
|
be done by running the following command on the _new_ database server:
|
|
|
|
```shell
|
|
sudo -u gitlab-psql /opt/gitlab/embedded/bin/slonik_create_set 1 --conf /var/opt/gitlab/postgresql/slony/slon_tools.conf | /opt/gitlab/embedded/bin/slonik
|
|
```
|
|
|
|
This should produce output along the lines of the following:
|
|
|
|
```plaintext
|
|
<stdin>:11: Subscription set 1 (set1) created
|
|
<stdin>:12: Adding tables to the subscription set
|
|
<stdin>:16: Add primary keyed table public.abuse_reports
|
|
<stdin>:20: Add primary keyed table public.appearances
|
|
<stdin>:24: Add primary keyed table public.application_settings
|
|
... more rows here ...
|
|
<stdin>:327: Adding sequences to the subscription set
|
|
<stdin>:328: All tables added
|
|
```
|
|
|
|
Finally we can start the replication process by running the following on the
|
|
_new_ database server:
|
|
|
|
```shell
|
|
sudo -u gitlab-psql /opt/gitlab/embedded/bin/slonik_subscribe_set 1 2 --conf /var/opt/gitlab/postgresql/slony/slon_tools.conf | /opt/gitlab/embedded/bin/slonik
|
|
```
|
|
|
|
This should produce the following output:
|
|
|
|
```plaintext
|
|
<stdin>:6: Subscribed nodes to set 1
|
|
```
|
|
|
|
At this point the new database server will start replicating the data of the old
|
|
database server. This process can take anywhere from a few minutes to hours, if
|
|
not days. Unfortunately Slony itself doesn't really provide a way of knowing
|
|
when the two databases are in sync. To get an estimate of the progress you can
|
|
use the following shell script:
|
|
|
|
```shell
|
|
#!/usr/bin/env bash
|
|
|
|
set -e
|
|
|
|
user='slony'
|
|
pass='SLONY_PASSWORD'
|
|
|
|
function main {
|
|
while :
|
|
do
|
|
local source
|
|
local target
|
|
|
|
source=$(PGUSER="${user}" PGPASSWORD="${pass}" /opt/gitlab/embedded/bin/psql -h OLD_HOST gitlabhq_production -c "select pg_size_pretty(pg_database_size('gitlabhq_production'));" -t -A)
|
|
target=$(PGUSER="${user}" PGPASSWORD="${pass}" /opt/gitlab/embedded/bin/psql -h NEW_HOST gitlabhq_production -c "select pg_size_pretty(pg_database_size('gitlabhq_production'));" -t -A)
|
|
|
|
echo "$(date): ${target} of ${source}" >> progress.log
|
|
echo "$(date): ${target} of ${source}"
|
|
|
|
sleep 60
|
|
done
|
|
}
|
|
|
|
main
|
|
```
|
|
|
|
This script will compare the sizes of the old and new database every minute and
|
|
print the result to STDOUT as well as logging it to a file. Make sure to replace
|
|
`SLONY_PASSWORD`, `OLD_HOST`, and `NEW_HOST` with the correct values.
|
|
|
|
## Stopping Replication
|
|
|
|
At some point the two databases are in sync. Once this is the case you'll need
|
|
to plan for a few minutes of downtime. This small downtime window is used to
|
|
stop the replication process, remove any Slony data from both databases, restart
|
|
GitLab so it can use the new database, etc.
|
|
|
|
First, let's stop all of GitLab. Omnibus users can do so by running the
|
|
following on their GitLab server(s):
|
|
|
|
```shell
|
|
sudo gitlab-ctl stop unicorn
|
|
sudo gitlab-ctl stop sidekiq
|
|
sudo gitlab-ctl stop mailroom
|
|
```
|
|
|
|
If you have any other processes that use PostgreSQL you should also stop those.
|
|
|
|
Once everything has been stopped you should update any configuration settings,
|
|
DNS records, etc so they all point to the new database.
|
|
|
|
Once the settings have been taken care of we need to stop the replication
|
|
process. It's crucial that no new data is written to the databases at this point
|
|
as this data will be lost.
|
|
|
|
To stop replication, run the following on both database servers:
|
|
|
|
```shell
|
|
sudo -u gitlab-psql /opt/gitlab/embedded/bin/slon_kill --conf /var/opt/gitlab/postgresql/slony/slon_tools.conf
|
|
```
|
|
|
|
This will stop all the Slony processes on the host the command was executed on.
|
|
|
|
## Resetting Sequences
|
|
|
|
The above setup does not replicate database sequences, as such these must be
|
|
reset manually in the target database. You can use the following script for
|
|
this:
|
|
|
|
```shell
|
|
#!/usr/bin/env bash
|
|
set -e
|
|
|
|
function main {
|
|
local fix_sequences
|
|
local fix_owners
|
|
|
|
fix_sequences='/tmp/fix_sequences.sql'
|
|
fix_owners='/tmp/fix_owners.sql'
|
|
|
|
# The SQL queries were taken from
|
|
# https://wiki.postgresql.org/wiki/Fixing_Sequences
|
|
sudo gitlab-psql gitlabhq_production -t -c "
|
|
SELECT 'ALTER SEQUENCE '|| quote_ident(MIN(schema_name)) ||'.'|| quote_ident(MIN(seq_name))
|
|
||' OWNED BY '|| quote_ident(MIN(TABLE_NAME)) ||'.'|| quote_ident(MIN(column_name)) ||';'
|
|
FROM (
|
|
SELECT
|
|
n.nspname AS schema_name,
|
|
c.relname AS TABLE_NAME,
|
|
a.attname AS column_name,
|
|
SUBSTRING(d.adsrc FROM E'^nextval\\(''([^'']*)''(?:::text|::regclass)?\\)') AS seq_name
|
|
FROM pg_class c
|
|
JOIN pg_attribute a ON (c.oid=a.attrelid)
|
|
JOIN pg_attrdef d ON (a.attrelid=d.adrelid AND a.attnum=d.adnum)
|
|
JOIN pg_namespace n ON (c.relnamespace=n.oid)
|
|
WHERE has_schema_privilege(n.oid,'USAGE')
|
|
AND n.nspname NOT LIKE 'pg!_%' escape '!'
|
|
AND has_table_privilege(c.oid,'SELECT')
|
|
AND (NOT a.attisdropped)
|
|
AND d.adsrc ~ '^nextval'
|
|
) seq
|
|
GROUP BY seq_name HAVING COUNT(*)=1;
|
|
" > "${fix_owners}"
|
|
|
|
sudo gitlab-psql gitlabhq_production -t -c "
|
|
SELECT 'SELECT SETVAL(' ||
|
|
quote_literal(quote_ident(PGT.schemaname) || '.' || quote_ident(S.relname)) ||
|
|
', COALESCE(MAX(' ||quote_ident(C.attname)|| '), 1) ) FROM ' ||
|
|
quote_ident(PGT.schemaname)|| '.'||quote_ident(T.relname)|| ';'
|
|
FROM pg_class AS S,
|
|
pg_depend AS D,
|
|
pg_class AS T,
|
|
pg_attribute AS C,
|
|
pg_tables AS PGT
|
|
WHERE S.relkind = 'S'
|
|
AND S.oid = D.objid
|
|
AND D.refobjid = T.oid
|
|
AND D.refobjid = C.attrelid
|
|
AND D.refobjsubid = C.attnum
|
|
AND T.relname = PGT.tablename
|
|
ORDER BY S.relname;
|
|
" > "${fix_sequences}"
|
|
|
|
sudo gitlab-psql gitlabhq_production -f "${fix_owners}"
|
|
sudo gitlab-psql gitlabhq_production -f "${fix_sequences}"
|
|
|
|
rm "${fix_owners}" "${fix_sequences}"
|
|
}
|
|
|
|
main
|
|
```
|
|
|
|
Upload this script to the _target_ server and execute it as follows:
|
|
|
|
```shell
|
|
bash path/to/the/script/above.sh
|
|
```
|
|
|
|
This will correct the ownership of sequences and reset the next value for the
|
|
`id` column to the next available value.
|
|
|
|
## Removing Slony
|
|
|
|
Next we need to remove all Slony related data. To do so, run the following
|
|
command on the _target_ server:
|
|
|
|
```shell
|
|
sudo gitlab-psql gitlabhq_production -c "DROP SCHEMA _slony_replication CASCADE;"
|
|
```
|
|
|
|
Once done you can safely remove any Slony related files (e.g. the log
|
|
directory), and uninstall Slony if desired. At this point you can start your
|
|
GitLab instance again and if all went well it should be using your new database
|
|
server.
|