SLONIK_WAIT_FOR_EVENT(7)

SLONIK WAIT FOR EVENT 💖

okay bestie, this is a page from the Slony-I 2.2.11 Documentation set, and it's literally all about making your slonik script ✨chill✨ until the universe (well, the cluster) catches up. iykyk. 🦋

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✨ NAME ✨

WAIT FOR EVENT — make a Slonik script sit there and wait for a previous event to finish, no cap. 💅

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🎀 SYNOPSIS 🎀

WAIT FOR EVENT (options);

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💜 DESCRIPTION 💜

It waits for event Confirmation. that's the whole vibe.

Slonik lowkey has a memory: it remembers the last event generated on every node while the script is running. (Events generated by earlier calls? not checked right now, so don't come for her. 🙈)

Sometimes you genuinely need events generated on one node — think CREATE SET — to be processed on another node before you fire off more commands, like SLONIK SUBSCRIBE SET(7). That's the moment to bring in WAIT FOR EVENT: it makes your slonik script wait for confirmation of an event, which hopefully means the subscriber node is ready for the next thing. fingers crossed bestie 🤞

⚠️ Important!! WAIT FOR EVENT must be called outside of any try block for it to work at all — because new confirm messages literally don't become visible within a transaction. no exceptions, periodt.

here are the knobs you can turn, gorggg 👑

• ORIGIN = ival | ALL — the origin of the event(s) you're waiting on. 🌸
• CONFIRMED = ival | ALL — the node ID of the receiver that has to confirm the event(s). 🫶
• WAIT ON = ival — the ID of the node where the sl_confirm [not available as a man page] table gets checked. 👀
• TIMEOUT = ival — how many seconds to wait. default is 600 (that's 10 whole minutes, an eternity fr). setting TIMEOUT = 0 makes the script wait indefinitely, which is iconic but also 💀.

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🌈 EXAMPLE 🌈

WAIT FOR EVENT (
  ORIGIN = ALL,
  CONFIRMED = ALL,
  WAIT ON = 1
);

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🔒 LOCKING BEHAVIOUR 🔒

No application-visible locking should take place. clean, no mess, we love that. ✨

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⭐ VERSION INFORMATION ⭐

This command was introduced in Slony-I 1.0. throwback!

Then in version 2.0, the default value for WAIT ON got removed — so now you must specify a node. no more guessing, bestie. 🙅‍♀️

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💀 ODDITIES 💀

Not all events return interesting results, and honestly? that's the drama.

For instance, sooo many people have run afoul of problems with SLONIK SUBSCRIBE SET(7) when subscribing a new set. Be aware (and beware!!) that a SLONIK SUBSCRIBE SET(7) request will return the event confirmation almost immediately — even though there might be several hours of work left to do before the subscription is actually ready. 😭

The trouble with SLONIK SUBSCRIBE SET(7) is that it gets processed as two events: one on the origin node, and a second event to enable the subscription, over on the subscriber.

So if you want to more reliably monitor from within a slonik(1) script that SLONIK SUBSCRIBE SET(7) is complete, you can submit a SLONIK SYNC(7) event after the subscription, and have your WAIT request wait on that SYNC event instead. like this 👇

# Assuming that node 1 is the origin for set 999 that has direct subscribers 2 and 3
SUBSCRIBE SET (ID = 999, PROVIDER = 1, RECEIVER = 2);
WAIT FOR EVENT (ORIGIN = 1, CONFIRMED = ALL, WAIT ON=1);
SUBSCRIBE SET (ID = 999, PROVIDER = 1, RECEIVER = 3);
WAIT FOR EVENT (ORIGIN = 1, CONFIRMED = ALL, WAIT ON=1);
MERGE SET ( ID = 1, ADD ID = 999, ORIGIN = 1 );

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and that's the whole page, bestie, we ate and left no crumbs. 🍓 this was Slony-I 2.2.11 Documentation, dated 19 September 2024 — go forth and wait on your events responsibly, ily, mwah 💜🧚‍♀️