[3.0] Sync PostgreSQL sequences with the rows the installer inserts

[albertlast]

Description

On a freshly installed PostgreSQL forum, the first topic anybody starts is silently not created.

The table schemas carry initial data with explicit IDs — the default board is board 1, and other seeded rows refer to each other by number — so those values are supplied to the INSERT rather than generated. MySQL notices a value above its AUTO_INCREMENT counter and moves the counter along by itself. PostgreSQL does not: a sequence only advances when something calls nextval() on it, nothing has, so it still sits at 1 and hands 1 to the next insert. That collides with the row already there:

ERROR:  duplicate key value violates unique constraint "smf_topics_pkey"
ERROR:  duplicate key value violates unique constraint "smf_messages_pkey"

28 sequences are in that state on a new install — boards, categories, membergroups, smileys, attachments, polls, personal_messages, scheduled_tasks and more.

What makes it easy to miss rather than easy to report:

• It does not look like a database problem. Post2 runs on to its normal redirect, the browser lands on the board, and the topic simply is not there. Nothing is shown to the user and nothing reaches log_errors.
• It fixes itself after one attempt. The insert that failed still consumed the 1, so the retry gets 2 and succeeds. Anyone who tries again concludes it was a fluke, and the forum behaves correctly from then on.

Because of that second point it only reproduces on a forum that has just been installed, which is why it has survived this long.

The fix

Table::populate() already works out which column auto-increments, in order to decide its insert mode. After the insert it now points the generator past what it just wrote. On MySQL this returns immediately.

This is not a new idea in the codebase: the 2.1 upgrade path has carried the same setval() for years, as Sources/Maintenance/Migration/v2_1/PostgreSqlSequences.php. Installs never got the equivalent.

Testing

The unit suite cannot reach this — it needs a database, and the state only exists on a forum that has just been installed.

Verified by hand on both engines, installing from scratch each time:

• PostgreSQL, before: starting the first topic returns 302 to the board and creates nothing; the PostgreSQL log shows the duplicate key errors above; pg_sequences.last_value is NULL for 28 sequences.
• PostgreSQL, after: no seeded table's sequence is left uncalled, and the first topic and its first reply post normally.
• MySQL: reinstalled and exercised as well, since populate() is shared. Unchanged, as expected.

Issues References (Fixes|Related|Closes)

Found while running HTTP tests against a freshly installed forum in #9347. Not otherwise reported that I can find.

[sbulen]

My recommendation is to cut over to Identity Columns in 3.0.

https://www.simplemachines.org/community/index.php?topic=592387.0

[albertlast]

i know, but this is here a bug fix pr, not feature pr ^^