Usability Challenges

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This page is for tracking my (Peter Eisentraut) current R & D project on Usability Challenges in the PostgreSQL system.

Contents

Core server management and configuration

  • Too much tuning
    • Memory management: too complex, there are few useful guidelines, most things could be automated
    • Vacuum: should be automatic -- yay, autovacuum
    • Background writer configuration: Who needs that?
    • Write-ahead log configuration: too complicated, should be automatic
    • Free-space map: The server knows full well how much FSM it needs; see also memory management.
  • Managability is lacking
    • User accounts: still no good way to manage pg_hba.conf from SQL
    • Statistics: too much data but most people don't know what to make of it
    • Configuration files: too long, too many options that most people don't need
    • Plugins: Using external modules is complicated, sometimes risky, hard to manage.
    • Logging: Logging configurability is great but the default configuration is less than useful for new users.
    • Tracing: Everything notwithstanding, it is still really hard at times to know what is happening, such as in nested PL/pgSQL calls, in cascaded foreign key actions, and other nested and cascaded contexts.* Clients:
    • Health checking: Most people cannot even tell that their system might be misconfigured. Help them.
    • No out-of-band monitoring is supported. If pg_ctl launched the postmaster but the postmaster can't start properly functioning backends, the only diagnostics are free-form text logs. This stinks for people trying to manage and automate PostgreSQL installs. An out-of-band monitoring tool is needed that can report things like the port(s) Pg is listening on, any errors produced when trying to start backends, memory status, running queries (w/o having to start a new backend just to query pg_stat_activity), lock status, etc. A command that chats with the postmaster by passing messages over shared memory would make sense, since if the postmaster successfully launched it bound to shm successfully.
  • Database dumps aren't portable between different OSes because Pg uses OS-specific locale names and localisation implementation from the C library. A database created on one operating system may not necessarily be restorable to a different operating system without encoding conversion (which pg_restore and psql offers no tools for) or at minimum a manual CREATE DATABASE with a hopefully-compatible locale name.

psql

  • psql isn't good for robust, reliable automation and scripting. It's great for interactive use, but try to configure it for noninteractive use with proper error checking and useful output. --- It's a mess. Also noted in this research paper commentary.


Backups, pg_dump, pg_dumpall and pg_restore

  • The default encodings/locales selected on Windows and Linux (UTF8) systems are incompatible with each other, so running pg_dump -Fc -f dbname.backup dbname on Linux then pg_restore -C --dbname postgres dbname.backup on Windows (or vice versa) will fail to create the database and abort the restore! with an unhelpful error like could not execute query: ERROR: invalid locale name en_US.UTF-8. Not cool! We need an encoding/locale equivalence table, and for future versions need some OS-independent locales or mappings in the server its self. See point above about OS dependent locales in core server.
  • There's no database that pg_dumpall and pg_restore --create can connect to that's guaranteed to always exist. The user shouldn't have to specify a database for either of these commands - it's actively counter-intuitive - but since both postgres and template1 can be dropped and template0 can't be connected to, there's no DB they can always connect to by default. This leads to weird command lines like pg_restore --create --dbname postgres mydb.backup to restore to a newly created database, probably but not necessarily called mydb, not to the postgres database. If the user omits --dbname they get a dump of the SQL of the restore to the console! This isn't good usability; these tools should have a read-only, non-droppable, always-available database they can always connect to when doing database-independent operations.
  • pg_dump doesn't global objects a database depends on, even when in -Fc mode. This means that by default PostgreSQL database dumps cannot be restored correctly unless the user dumps additional information separately!. pg_dump should include global objects like roles that are referred to by the database being dumped, so that backups are complete and correct by default.
  • pg_dumpall doesn't support the custom format. You can't make an archive containing all databases on a cluster, or have it spit out one dump file per database plus a globals file. This must be done manually using scripting, and that's rather less than user friendly. Backups need to be easy to get right by default!
  • pg_restore -C doesn't let you choose what name you want for the new database, it forces it to the name the DB was dumped as. If you want a different name you have to manually create the DB with the correct encoding, permissions, ownership, roles, etc.
  • pg_restore doesn't encourage the use of the .backup file extension expected by PgAdmin-III

PgAdmin-III (First point of contact for most newbies)

  • PgAdmin-III usability may be somewhat lacking
  • Using the "Restore" dialog with PgAdmin-III and pointing it a .sql dump produces an unhelpful error message. It should offer to run the SQL dump against the target database, at least when faced with a pg_dump sql dump containing its handy "--- PostgreSQL database dump" header (though that might get localised, need to check)
  • PgAdmin-III offers no easy way to run an SQL script that may contain psql commands like \connect. Since pg_dump emits psql commands in dumps by default, that means users can't use the PgAdmin-III gui to restore an SQL dump.
  • SQL scripts loaded into PgAdmin-III's SQL editor are wrapped in a transaction automatically and silently by PgAdmin-III. If any statement fails, the whole script fails. Because pg_dump likes to generate statements like \connect dbname and CREATE ROLE postgres; in dumps, this means dumps have to be edited by hand before they can be restored.
  • PgAdmin-III uses the unhelpful .backup suffix for backups it creates with pg_dump -Fc behind the scenes. Backup of what? There's nothing in pg_restore that says files should have a .backup extension, nor does it encourage them to be created as such, so users who want to restore a backup created from the command line via PgAdmin-III often have to rename the file or change the filter before they can even see it in the file list to restore.
  • It doesn't register a file extension handler for .backup files
  • It doesn't understand .backup files if you drag and drop them onto PgAdmin-III or pass them as command-line arguments to the pgadmin3 executable, and doesn't offer a file->open menu item
  • You have to select a database in PgAdmin-III before you can restore a .backup file - even if you intend to check the "Create database" option that uses pg_restore's -C option. That's really counter-intuitive; you should just be able to select the server you want to restore to, or use the restore item in the menu and be prompted for the target server.
  • You don't get a choice of the database name to use for the newly created database with PgAdmin-III's Restore, Create Database option, it silently uses the db name in the backup file (and doesn't give you any indication of what it is). This is a pg_restore limitation.
  • PgAdmin-III's user interface blocks whenever its running a pg_dump<code> or <code>pg_restore job, so it feels like it's crashed/hung to a normal user.
  • PgAdmin-III gives no guidance about why restore commands failed, just spitting out the command line output from pg_restore.

Replication

  • Built-in replication can't replicate only some databases of a cluster; you have to replicate both my-critically-important-10MB-database and my-totally-unimportant-50GB-database with the same settings, same priority, etc. This is a usability challenge because it means people have to create and manage multiple clusters to control replication groups, and multiple clusters are hard to manage and configure.

See also Usability reviews

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