PgLoader Reference Manual

pgloader loads data from various sources into PostgreSQL. It can transform the data it reads on the fly and submit raw SQL before and after the loading. It uses the COPY PostgreSQL protocol to stream the data into the server, and manages errors by filling a pair of reject.dat and reject.log files.

pgloader operates either using commands which are read from files:

pgloader commands.load

or by using arguments and options all provided on the command line:

pgloader SOURCE TARGET

Arguments

The pgloader arguments can be as many load files as needed, or a couple of connection strings to a specific input file.

Source Connection String

The source connection string format is as follows:

format:///absolute/path/to/file.ext
format://./relative/path/to/file.ext

Where format might be one of csv, fixed, copy, dbf, db3 or ixf.:

db://user:pass@host:port/dbname

Where db might be of sqlite, mysql or mssql.

When using a file based source format, pgloader also support natively fetching the file from an http location and decompressing an archive if needed. In that case it’s necessary to use the –type option to specify the expected format of the file. See the examples below.

Also note that some file formats require describing some implementation details such as columns to be read and delimiters and quoting when loading from csv.

For more complex loading scenarios, you will need to write a full fledge load command in the syntax described later in this document.

Target Connection String

The target connection string format is described in details later in this document, see Section Connection String.

Options

Inquiry Options

Use these options when you want to know more about how to use pgloader, as those options will cause pgloader not to load any data.

  • -h, –help

    Show command usage summary and exit.

  • -V, –version

    Show pgloader version string and exit.

  • -E, –list-encodings

    List known encodings in this version of pgloader.

  • -U, –upgrade-config

    Parse given files in the command line as pgloader.conf files with the INI syntax that was in use in pgloader versions 2.x, and output the new command syntax for pgloader on standard output.

General Options

Those options are meant to tweak pgloader behavior when loading data.

  • -v, –verbose

    Be verbose.

  • -q, –quiet

    Be quiet.

  • -d, –debug

    Show debug level information messages.

  • -D, –root-dir

    Set the root working directory (default to “/tmp/pgloader”).

  • -L, –logfile

    Set the pgloader log file (default to “/tmp/pgloader/pgloader.log”).

  • –log-min-messages

    Minimum level of verbosity needed for log message to make it to the logfile. One of critical, log, error, warning, notice, info or debug.

  • –client-min-messages

    Minimum level of verbosity needed for log message to make it to the console. One of critical, log, error, warning, notice, info or debug.

  • -S, –summary

    A filename where to copy the summary output. When relative, the filename is expanded into *root-dir*.

    The format of the filename defaults to being human readable. It is possible to have the output in machine friendly formats such as CSV, COPY (PostgreSQL’s own COPY format) or JSON by specifying a filename with the extension resp. .csv, .copy or .json.

  • -l <file>, –load-lisp-file <file>

    Specify a lisp <file> to compile and load into the pgloader image before reading the commands, allowing to define extra transformation function. Those functions should be defined in the pgloader.transforms package. This option can appear more than once in the command line.

  • –dry-run

    Allow testing a .load file without actually trying to load any data. It’s useful to debug it until it’s ok, in particular to fix connection strings.

  • –on-error-stop

    Alter pgloader behavior: rather than trying to be smart about error handling and continue loading good data, separating away the bad one, just stop as soon as PostgreSQL refuses anything sent to it. Useful to debug data processing, transformation function and specific type casting.

  • –self-upgrade <directory>

    Specify a <directory> where to find pgloader sources so that one of the very first things it does is dynamically loading-in (and compiling to machine code) another version of itself, usually a newer one like a very recent git checkout.

  • –no-ssl-cert-verification

    Uses the OpenSSL option to accept a locally issued server-side certificate, avoiding the following error message:

    SSL verify error: 20 X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY
    

    The right way to fix the SSL issue is to use a trusted certificate, of course. Sometimes though it’s useful to make progress with the pgloader setup while the certificate chain of trust is being fixed, maybe by another team. That’s when this option is useful.

Command Line Only Operations

Those options are meant to be used when using pgloader from the command line only, rather than using a command file and the rich command clauses and parser. In simple cases, it can be much easier to use the SOURCE and TARGET directly on the command line, then tweak the loading with those options:

  • –with “option”

    Allows setting options from the command line. You can use that option as many times as you want. The option arguments must follow the WITH clause for the source type of the SOURCE specification, as described later in this document.

  • –set “guc_name=’value’”

    Allows setting PostgreSQL configuration from the command line. Note that the option parsing is the same as when used from the SET command clause, in particular you must enclose the guc value with single-quotes.

  • –field “…”

    Allows setting a source field definition. Fields are accumulated in the order given on the command line. It’s possible to either use a –field option per field in the source file, or to separate field definitions by a comma, as you would do in the HAVING FIELDS clause.

  • –cast “…”

    Allows setting a specific casting rule for loading the data.

  • –type csv|fixed|db3|ixf|sqlite|mysql|mssql

    Allows forcing the source type, in case when the SOURCE parsing isn’t satisfying.

  • –encoding <encoding>

    Set the encoding of the source file to load data from.

  • –before <filename>

    Parse given filename for SQL queries and run them against the target database before loading the data from the source. The queries are parsed by pgloader itself: they need to be terminated by a semi-colon (;) and the file may include i or ir commands to include another file.

  • –after <filename>

    Parse given filename for SQL queries and run them against the target database after having loaded the data from the source. The queries are parsed in the same way as with the –before option, see above.

More Debug Information

To get the maximum amount of debug information, you can use both the –verbose and the –debug switches at the same time, which is equivalent to saying –client-min-messages data. Then the log messages will show the data being processed, in the cases where the code has explicit support for it.

Batches And Retry Behaviour

To load data to PostgreSQL, pgloader uses the COPY streaming protocol. While this is the faster way to load data, COPY has an important drawback: as soon as PostgreSQL emits an error with any bit of data sent to it, whatever the problem is, the whole data set is rejected by PostgreSQL.

To work around that, pgloader cuts the data into batches of 25000 rows each, so that when a problem occurs it’s only impacting that many rows of data. Each batch is kept in memory while the COPY streaming happens, in order to be able to handle errors should some happen.

When PostgreSQL rejects the whole batch, pgloader logs the error message then isolates the bad row(s) from the accepted ones by retrying the batched rows in smaller batches. To do that, pgloader parses the CONTEXT error message from the failed COPY, as the message contains the line number where the error was found in the batch, as in the following example:

CONTEXT: COPY errors, line 3, column b: "2006-13-11"

Using that information, pgloader will reload all rows in the batch before the erroneous one, log the erroneous one as rejected, then try loading the remaining of the batch in a single attempt, which may or may not contain other erroneous data.

At the end of a load containing rejected rows, you will find two files in the root-dir location, under a directory named the same as the target database of your setup. The filenames are the target table, and their extensions are .dat for the rejected data and .log for the file containing the full PostgreSQL client side logs about the rejected data.

The .dat file is formatted in PostgreSQL the text COPY format as documented in http://www.postgresql.org/docs/9.2/static/sql-copy.html#AEN66609.

It is possible to use the following WITH options to control pgloader batch behavior:

  • on error stop, on error resume next

    This option controls if pgloader is using building batches of data at all. The batch implementation allows pgloader to recover errors by sending the data that PostgreSQL accepts again, and by keeping away the data that PostgreSQL rejects.

    To enable retrying the data and loading the good parts, use the option on error resume next, which is the default to file based data loads (such as CSV, IXF or DBF).

    When migrating from another RDMBS technology, it’s best to have a reproducible loading process. In that case it’s possible to use on error stop and fix either the casting rules, the data transformation functions or in cases the input data until your migration runs through completion. That’s why on error resume next is the default for SQLite, MySQL and MS SQL source kinds.

A Note About Performance

pgloader has been developed with performance in mind, to be able to cope with ever growing needs in loading large amounts of data into PostgreSQL.

The basic architecture it uses is the old Unix pipe model, where a thread is responsible for loading the data (reading a CSV file, querying MySQL, etc) and fills pre-processed data into a queue. Another threads feeds from the queue, apply some more transformations to the input data and stream the end result to PostgreSQL using the COPY protocol.

When given a file that the PostgreSQL COPY command knows how to parse, and if the file contains no erroneous data, then pgloader will never be as fast as just using the PostgreSQL COPY command.

Note that while the COPY command is restricted to read either from its standard input or from a local file on the server’s file system, the command line tool psql implements a copy command that knows how to stream a file local to the client over the network and into the PostgreSQL server, using the same protocol as pgloader uses.

A Note About Parallelism

pgloader uses several concurrent tasks to process the data being loaded:

  • a reader task reads the data in and pushes it to a queue,
  • at last one write task feeds from the queue and formats the raw into the PostgreSQL COPY format in batches (so that it’s possible to then retry a failed batch without reading the data from source again), and then sends the data to PostgreSQL using the COPY protocol.

The parameter workers allows to control how many worker threads are allowed to be active at any time (that’s the parallelism level); and the parameter concurrency allows to control how many tasks are started to handle the data (they may not all run at the same time, depending on the workers setting).

We allow workers simultaneous workers to be active at the same time in the context of a single table. A single unit of work consist of several kinds of workers:

  • a reader getting raw data from the source,
  • N writers preparing and sending the data down to PostgreSQL.

The N here is setup to the concurrency parameter: with a CONCURRENCY of 2, we start (+ 1 2) = 3 concurrent tasks, with a concurrency of 4 we start (+ 1 4) = 5 concurrent tasks, of which only workers may be active simultaneously.

The defaults are workers = 4, concurrency = 1 when loading from a database source, and workers = 8, concurrency = 2 when loading from something else (currently, a file). Those defaults are arbitrary and waiting for feedback from users, so please consider providing feedback if you play with the settings.

As the CREATE INDEX threads started by pgloader are only waiting until PostgreSQL is done with the real work, those threads are NOT counted into the concurrency levels as detailed here.

By default, as many CREATE INDEX threads as the maximum number of indexes per table are found in your source schema. It is possible to set the max parallel create index WITH option to another number in case there’s just too many of them to create.

Source Formats

pgloader supports the following input formats:

  • csv, which includes also tsv and other common variants where you can change the separator and the quoting rules and how to escape the quotes themselves;
  • fixed columns file, where pgloader is flexible enough to accomodate with source files missing columns (ragged fixed length column files do exist);
  • PostgreSLQ COPY formatted files, following the COPY TEXT documentation of PostgreSQL, such as the reject files prepared by pgloader;
  • dbase files known as db3 or dbf file;
  • ixf formated files, ixf being a binary storage format from IBM;
  • sqlite databases with fully automated discovery of the schema and advanced cast rules;
  • mysql databases with fully automated discovery of the schema and advanced cast rules;
  • MS SQL databases with fully automated discovery of the schema and advanced cast rules.

Pgloader Commands Syntax

pgloader implements a Domain Specific Language allowing to setup complex data loading scripts handling computed columns and on-the-fly sanitization of the input data. For more complex data loading scenarios, you will be required to learn that DSL’s syntax. It’s meant to look familiar to DBA by being inspired by SQL where it makes sense, which is not that much after all.

The pgloader commands follow the same global grammar rules. Each of them might support only a subset of the general options and provide specific options.

LOAD <source-type>
         FROM <source-url>
       [ HAVING FIELDS <source-level-options> ]
             INTO <postgresql-url>
       [ TARGET TABLE [ "<schema>" ]."<table name>" ]
       [ TARGET COLUMNS <columns-and-options> ]

    [ WITH <load-options> ]

    [ SET <postgresql-settings> ]

[ BEFORE LOAD [ DO <sql statements> | EXECUTE <sql file> ] ... ]
[  AFTER LOAD [ DO <sql statements> | EXECUTE <sql file> ] ... ]
    ;

The main clauses are the LOAD, FROM, INTO and WITH clauses that each command implements. Some command then implement the SET command, or some specific clauses such as the CAST clause.

Templating with Mustache

pgloader implements the https://mustache.github.io/ templating system so that you may have dynamic parts of your commands. See the documentation for this template system online.

A specific feature of pgloader is the ability to fetch a variable from the OS environment of the pgloader process, making it possible to run pgloader as in the following example:

$ DBPATH=sqlite/sqlite.db pgloader ./test/sqlite-env.load

or in several steps:

$ export DBPATH=sqlite/sqlite.db
$ pgloader ./test/sqlite-env.load

The variable can then be used in a typical mustache fashion:

load database
     from '{{DBPATH}}'
     into postgresql:///pgloader;

It’s also possible to prepare a INI file such as the following:

[pgloader]

DBPATH = sqlite/sqlite.db

And run the following command, feeding the INI values as a context for pgloader templating system:

$ pgloader --context ./test/sqlite.ini ./test/sqlite-ini.load

The mustache templates implementation with OS environment support replaces former GETENV implementation, which didn’t work anyway.

Common Clauses

Some clauses are common to all commands:

FROM

The FROM clause specifies where to read the data from, and each command introduces its own variant of sources. For instance, the CSV source supports inline, stdin, a filename, a quoted filename, and a FILENAME MATCHING clause (see above); whereas the MySQL source only supports a MySQL database URI specification.

INTO

The PostgreSQL connection URI must contains the name of the target table where to load the data into. That table must have already been created in PostgreSQL, and the name might be schema qualified.

Then INTO option also supports an optional comma separated list of target columns, which are either the name of an input field or the white space separated list of the target column name, its PostgreSQL data type and a USING expression.

The USING expression can be any valid Common Lisp form and will be read with the current package set to pgloader.transforms, so that you can use functions defined in that package, such as functions loaded dynamically with the –load command line parameter.

Each USING expression is compiled at runtime to native code.

This feature allows pgloader to load any number of fields in a CSV file into a possibly different number of columns in the database, using custom code for that projection.

WITH

Set of options to apply to the command, using a global syntax of either:

  • key = value
  • use option
  • do not use option

See each specific command for details.

All data sources specific commands support the following options:

  • on error stop, on error resume next
  • batch rows = R
  • batch size = … MB
  • prefetch rows = …

See the section BATCH BEHAVIOUR OPTIONS for more details.

In addition, the following settings are available:

  • workers = W
  • concurrency = C
  • max parallel create index = I

See section A NOTE ABOUT PARALLELISM for more details.

SET

This clause allows to specify session parameters to be set for all the sessions opened by pgloader. It expects a list of parameter name, the equal sign, then the single-quoted value as a comma separated list.

The names and values of the parameters are not validated by pgloader, they are given as-is to PostgreSQL.

BEFORE LOAD DO

You can run SQL queries against the database before loading the data from the CSV file. Most common SQL queries are CREATE TABLE IF NOT EXISTS so that the data can be loaded.

Each command must be dollar-quoted: it must begin and end with a double dollar sign, $$. Dollar-quoted queries are then comma separated. No extra punctuation is expected after the last SQL query.

BEFORE LOAD EXECUTE

Same behaviour as in the BEFORE LOAD DO clause. Allows you to read the SQL queries from a SQL file. Implements support for PostgreSQL dollar-quoting and the i and ir include facilities as in psql batch mode (where they are the same thing).

AFTER LOAD DO

Same format as BEFORE LOAD DO, the dollar-quoted queries found in that section are executed once the load is done. That’s the right time to create indexes and constraints, or re-enable triggers.

AFTER LOAD EXECUTE

Same behaviour as in the AFTER LOAD DO clause. Allows you to read the SQL queries from a SQL file. Implements support for PostgreSQL dollar-quoting and the i and ir include facilities as in psql batch mode (where they are the same thing).

AFTER CREATE SCHEMA DO

Same format as BEFORE LOAD DO, the dollar-quoted queries found in that section are executed once the schema has been craeted by pgloader, and before the data is loaded. It’s the right time to ALTER TABLE or do some custom implementation on-top of what pgloader does, like maybe partitioning.

AFTER CREATE SCHEMA EXECUTE

Same behaviour as in the AFTER CREATE SCHEMA DO clause. Allows you to read the SQL queries from a SQL file. Implements support for PostgreSQL dollar-quoting and the i and ir include facilities as in psql batch mode (where they are the same thing).

Connection String

The <postgresql-url> parameter is expected to be given as a Connection URI as documented in the PostgreSQL documentation at http://www.postgresql.org/docs/9.3/static/libpq-connect.html#LIBPQ-CONNSTRING.

postgresql://[user[:password]@][netloc][:port][/dbname][?option=value&...]

Where:

  • user

    Can contain any character, including colon (:) which must then be doubled (::) and at-sign (@) which must then be doubled (@@).

    When omitted, the user name defaults to the value of the PGUSER environment variable, and if it is unset, the value of the USER environment variable.

  • password

    Can contain any character, including the at sign (@) which must then be doubled (@@). To leave the password empty, when the user name ends with at at sign, you then have to use the syntax user:@.

    When omitted, the password defaults to the value of the PGPASSWORD environment variable if it is set, otherwise the password is left unset.

    When no password is found either in the connection URI nor in the environment, then pgloader looks for a .pgpass file as documented at https://www.postgresql.org/docs/current/static/libpq-pgpass.html. The implementation is not that of libpq though. As with libpq you can set the environment variable PGPASSFILE to point to a .pgpass file, and pgloader defaults to ~/.pgpass on unix like systems and %APPDATA%postgresqlpgpass.conf on windows. Matching rules and syntax are the same as with libpq, refer to its documentation.

  • netloc

    Can be either a hostname in dotted notation, or an ipv4, or an Unix domain socket path. Empty is the default network location, under a system providing unix domain socket that method is preferred, otherwise the netloc default to localhost.

    It’s possible to force the unix domain socket path by using the syntax unix:/path/to/where/the/socket/file/is, so to force a non default socket path and a non default port, you would have:

    postgresql://unix:/tmp:54321/dbname

    The netloc defaults to the value of the PGHOST environment variable, and if it is unset, to either the default unix socket path when running on a Unix system, and localhost otherwise.

    Socket path containing colons are supported by doubling the colons within the path, as in the following example:

    postgresql://unix:/tmp/project::region::instance:5432/dbname

  • dbname

    Should be a proper identifier (letter followed by a mix of letters, digits and the punctuation signs comma (,), dash (-) and underscore (_).

    When omitted, the dbname defaults to the value of the environment variable PGDATABASE, and if that is unset, to the user value as determined above.

  • options

    The optional parameters must be supplied with the form name=value, and you may use several parameters by separating them away using an ampersand (&) character.

    Only some options are supported here, tablename (which might be qualified with a schema name) sslmode, host, port, dbname, user and password.

    The sslmode parameter values can be one of disable, allow, prefer or require.

    For backward compatibility reasons, it’s possible to specify the tablename option directly, without spelling out the tablename= parts.

    The options override the main URI components when both are given, and using the percent-encoded option parameters allow using passwords starting with a colon and bypassing other URI components parsing limitations.

Regular Expressions

Several clauses listed in the following accept regular expressions with the following input rules:

  • A regular expression begins with a tilde sign (~),
  • is then followed with an opening sign,
  • then any character is allowed and considered part of the regular expression, except for the closing sign,
  • then a closing sign is expected.

The opening and closing sign are allowed by pair, here’s the complete list of allowed delimiters:

~//
~[]
~{}
~()
~<>
~""
~''
~||
~##

Pick the set of delimiters that don’t collide with the regular expression you’re trying to input. If your expression is such that none of the solutions allow you to enter it, the places where such expressions are allowed should allow for a list of expressions.

Comments

Any command may contain comments, following those input rules:

  • the delimiter begins a comment that ends with the end of the current line,
  • the delimiters /* and */ respectively start and end a comment, which can be found in the middle of a command or span several lines.

Any place where you could enter a whitespace will accept a comment too.

Batch behaviour options

All pgloader commands have support for a WITH clause that allows for specifying options. Some options are generic and accepted by all commands, such as the batch behaviour options, and some options are specific to a data source kind, such as the CSV skip header option.

The global batch behaviour options are:

  • batch rows

    Takes a numeric value as argument, used as the maximum number of rows allowed in a batch. The default is 25 000 and can be changed to try having better performance characteristics or to control pgloader memory usage;

  • batch size

    Takes a memory unit as argument, such as 20 MB, its default value. Accepted multipliers are kB, MB, GB, TB and PB. The case is important so as not to be confused about bits versus bytes, we’re only talking bytes here.

  • prefetch rows

    Takes a numeric value as argument, defaults to 100000. That’s the number of rows that pgloader is allowed to read in memory in each reader thread. See the workers setting for how many reader threads are allowed to run at the same time.

Other options are specific to each input source, please refer to specific parts of the documentation for their listing and covering.

A batch is then closed as soon as either the batch rows or the batch size threshold is crossed, whichever comes first. In cases when a batch has to be closed because of the batch size setting, a debug level log message is printed with how many rows did fit in the oversized batch.