@clickup/pg-microsharding/dist/internal/getSlotInfo.js

Microshards support for PostgreSQL

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.getSlotInfo = getSlotInfo;
const createConnectedClient_1 = require("./createConnectedClient");
const parseLsn_1 = require("./parseLsn");
/**
 * Returns the difference between src LSN and dst LSN (gap), along with some
 * estimation on how much seconds they are apart from each other. To measure
 * that time, we "latch" an LSN on the src and then wait until dst crosses that
 * latched LSN. Once it does, we remember the actual astronomical time it took
 * to cross, and then latch the src LSN again (towards the next estimation
 * cycle). When the caller decides that the time is small enough, it stops
 * polling; and if the time is large (e.g. more than 20 seconds), it continues
 * to call getSlotInfo() over and over again until that time drops below the
 * needed 20 seconds threshold.
 */
async function getSlotInfo({ dsn, slotName, }, prevSlotInfo) {
    const client = await (0, createConnectedClient_1.createConnectedClient)(dsn);
    try {
        const srcLsn = await client.currentWalInsertLsn();
        const dstLsn = await client.confirmedFlushLsn(slotName);
        const gap = (0, parseLsn_1.subtractLsn)(srcLsn, dstLsn);
        if (!prevSlotInfo) {
            prevSlotInfo = {
                srcLsn,
                dstLsn,
                gap,
                gapTillLatch: gap,
                lagSec: null, // means "unknown"
                latched: {
                    srcLsn,
                    at: performance.now(),
                },
            };
        }
        const gapTillLatch = (0, parseLsn_1.subtractLsn)(prevSlotInfo.latched.srcLsn, dstLsn);
        return gapTillLatch <= 0
            ? {
                srcLsn,
                dstLsn,
                gap,
                gapTillLatch,
                lagSec: Math.round((performance.now() - prevSlotInfo.latched.at) / 1000),
                latched: {
                    srcLsn,
                    at: performance.now(),
                },
            }
            : {
                srcLsn,
                dstLsn,
                gap,
                gapTillLatch,
                lagSec: prevSlotInfo.lagSec,
                latched: prevSlotInfo.latched,
            };
    }
    finally {
        await client.end().catch(() => { });
    }
}
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