storage.elasticsearch.bulkActions

文档：

Async bulk size of the record data batch execution.

源码：

// org.apache.skywalking.library.elasticsearch.bulk.BulkProcessor
public CompletableFuture<Void> add(UpdateRequest request) {
        return internalAdd(request);
    }

    @SneakyThrows
    private CompletableFuture<Void> internalAdd(Object request) {
        requireNonNull(request, "request");
        final CompletableFuture<Void> f = new CompletableFuture<>();
        requests.put(new Holder(f, request));
        flushIfNeeded();
        return f;
    }

    @SneakyThrows
    private void flushIfNeeded() {
        if (requests.size() >= bulkActions) {
            flush();
        }
    }

就是多少个update请求会作为一批，一块flush.

storage.elasticsearch.flushInterval

文档：

Period of flush (in seconds). Does not matter whether bulkActions is reached or not. INT(flushInterval * 2/3) is used for index refresh period.

源码1：

BulkProcessor(
        final AtomicReference<ElasticSearch> es, final int bulkActions,
        final Duration flushInterval, final int concurrentRequests) {
        。。。
        scheduler.scheduleWithFixedDelay(
            this::flush, 0, flushInterval.getSeconds(), TimeUnit.SECONDS);
    }

就是每隔多少秒flush一次。

源码2：org.apache.skywalking.oap.server.storage.plugin.elasticsearch.base.StorageEsInstaller#createSetting

protected Map<String, Object> createSetting(Model model) throws StorageException {
        Map<String, Object> setting = new HashMap<>();
        // Set the index refresh period as INT(flushInterval * 2/3). At the edge case,
        // in low traffic(traffic < bulkActions in the whole period), there is a possible case, 2 period bulks are included in
        // one index refresh rebuild operation, which could cause version conflicts. And this case can't be fixed
        // through `core/persistentPeriod` as the bulk fresh is not controlled by the persistent timer anymore.
        int indexRefreshInterval = config.getFlushInterval() * 2 / 3;
        if (indexRefreshInterval < 5) {
            // The refresh interval should not be less than 5 seconds (the recommended default value = 10s),
            // and the bulk flush interval should not be set less than 8s (the recommended default value = 15s).
            // This is a precaution case which makes ElasticSearch server has reasonable refresh interval,
            // even this value is set too small by end user manually.
            indexRefreshInterval = 5;
        }
        setting.put("index.refresh_interval", indexRefreshInterval + "s");
        return setting;
    }

就是设置index.refresh_interval的值。
因此，storage.elasticsearch.flushInterval这参数实际是有2个作用的。

storage.elasticsearch.concurrentRequests

文档：

The number of concurrent requests allowed to be executed.

源码：

//org.apache.skywalking.library.elasticsearch.bulk.BulkProcessor#BulkProcessor
BulkProcessor(
        this.bulkActions = bulkActions;
        this.semaphore = new Semaphore(concurrentRequests > 0 ? concurrentRequests : 1);
}
// org.apache.skywalking.library.elasticsearch.bulk.BulkProcessor#flush
void flush() {
        if (requests.isEmpty()) {
            return;
        }
        try {
            semaphore.acquire();
        } catch (InterruptedException e) {
            log.error("Interrupted when trying to get semaphore to execute bulk requests", e);
            return;
        }
    }

就是允许多少个线程并发的执行flush。

ps：文档在这里