pgloader

# Loading SQLite files with pgloader

The SQLite database is a respected solution to manage your data with. Its embeded nature makes it a source of migrations when a projects now needs to handle more concurrency, which PostgreSQL is very good at. pgloader can help you there.

## In a Single Command Line

You can

    $ createdb chinook
    $ pgloader https://github.com/lerocha/chinook-database/raw/master/ChinookDatabase/DataSources/Chinook_Sqlite_AutoIncrementPKs.sqlite pgsql:///chinook

Done! All with the schema, data, constraints, primary keys and foreign keys, etc. We also see an error with the Chinook schema that contains several primary key definitions against the same table, which is not accepted by PostgreSQL:

    2017-06-20T16:18:59.019000+02:00 LOG Data errors in '/private/tmp/pgloader/'
    2017-06-20T16:18:59.236000+02:00 LOG Fetching 'https://github.com/lerocha/chinook-database/raw/master/ChinookDatabase/DataSources/Chinook_Sqlite_AutoIncrementPKs.sqlite'
    2017-06-20T16:19:00.664000+02:00 ERROR Database error 42P16: multiple primary keys for table "playlisttrack" are not allowed
    QUERY: ALTER TABLE playlisttrack ADD PRIMARY KEY USING INDEX idx_66873_sqlite_autoindex_playlisttrack_1;
    2017-06-20T16:19:00.665000+02:00 LOG report summary reset
                 table name       read   imported     errors      total time
    -----------------------  ---------  ---------  ---------  --------------
                      fetch          0          0          0          0.877s
            fetch meta data         33         33          0          0.033s
             Create Schemas          0          0          0          0.003s
           Create SQL Types          0          0          0          0.006s
              Create tables         22         22          0          0.043s
             Set Table OIDs         11         11          0          0.012s
    -----------------------  ---------  ---------  ---------  --------------
                      album        347        347          0          0.023s
                     artist        275        275          0          0.023s
                   customer         59         59          0          0.021s
                   employee          8          8          0          0.018s
                    invoice        412        412          0          0.031s
                      genre         25         25          0          0.021s
                invoiceline       2240       2240          0          0.034s
                  mediatype          5          5          0          0.025s
              playlisttrack       8715       8715          0          0.040s
                   playlist         18         18          0          0.016s
                      track       3503       3503          0          0.111s
    -----------------------  ---------  ---------  ---------  --------------
    COPY Threads Completion         33         33          0          0.313s
             Create Indexes         22         22          0          0.160s
     Index Build Completion         22         22          0          0.027s
            Reset Sequences          0          0          0          0.017s
               Primary Keys         12          0          1          0.013s
        Create Foreign Keys         11         11          0          0.040s
            Create Triggers          0          0          0          0.000s
           Install Comments          0          0          0          0.000s
    -----------------------  ---------  ---------  ---------  --------------
          Total import time      15607      15607          0          1.669s

You may need to have special cases to take care of tho. In advanced case you can use the pgloader command.

## The Command

To load data with pgloader you need to define in a command the operations in some details. Here's our command:

    load database
         from 'sqlite/Chinook_Sqlite_AutoIncrementPKs.sqlite'
         into postgresql:///pgloader

     with include drop, create tables, create indexes, reset sequences

      set work_mem to '16MB', maintenance_work_mem to '512 MB';

You can see the full list of options in the pgloader reference manual, with a complete description of the options you see here.

Note that here pgloader will benefit from the meta-data information found in the SQLite file to create a PostgreSQL database capable of hosting the data as described, then load the data.

## Loading the data

Let's start the `pgloader` command with our `sqlite.load` command file:

    $ pgloader sqlite.load
    ... LOG Starting pgloader, log system is ready.
    ... LOG Parsing commands from file "/Users/dim/dev/pgloader/test/sqlite.load"
    ... WARNING Postgres warning: table "album" does not exist, skipping
    ... WARNING Postgres warning: table "artist" does not exist, skipping
    ... WARNING Postgres warning: table "customer" does not exist, skipping
    ... WARNING Postgres warning: table "employee" does not exist, skipping
    ... WARNING Postgres warning: table "genre" does not exist, skipping
    ... WARNING Postgres warning: table "invoice" does not exist, skipping
    ... WARNING Postgres warning: table "invoiceline" does not exist, skipping
    ... WARNING Postgres warning: table "mediatype" does not exist, skipping
    ... WARNING Postgres warning: table "playlist" does not exist, skipping
    ... WARNING Postgres warning: table "playlisttrack" does not exist, skipping
    ... WARNING Postgres warning: table "track" does not exist, skipping
                table name       read   imported     errors            time
    ----------------------  ---------  ---------  ---------  --------------
          create, truncate          0          0          0          0.052s
                     Album        347        347          0          0.070s
                    Artist        275        275          0          0.014s
                  Customer         59         59          0          0.014s
                  Employee          8          8          0          0.012s
                     Genre         25         25          0          0.018s
                   Invoice        412        412          0          0.032s
               InvoiceLine       2240       2240          0          0.077s
                 MediaType          5          5          0          0.012s
                  Playlist         18         18          0          0.008s
             PlaylistTrack       8715       8715          0          0.071s
                     Track       3503       3503          0          0.105s
    index build completion          0          0          0          0.000s
    ----------------------  ---------  ---------  ---------  --------------
            Create Indexes         20         20          0          0.279s
           reset sequences          0          0          0          0.043s
    ----------------------  ---------  ---------  ---------  --------------
      Total streaming time      15607      15607          0          0.476s

We can see that http://pgloader.io did download the file from its HTTP URL location then unziped it before loading it.

Also, the WARNING messages we see here are expected as the PostgreSQL database is empty when running the command, and pgloader is using the SQL commands `DROP TABLE IF EXISTS` when the given command uses the `include drop` option.

Note that the output of the command has been edited to facilitate its browsing online.