KSQLDB Emit Final 不返回任何值

问题描述

如果我使用EMIT CHANGES"，我会在 ksqldb 上进行以下查询；它确实有效，但如果将其更改为EMIT FINAL"窗口结束后不返回任何值

I've following query on ksqldb , if I use "EMIT CHANGES" it does work, but if change it to "EMIT FINAL" it does not return any value after the window end

 CREATE TABLE sspc_3536660_v4 as select sspc,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_ds_cir_fulfillment' THEN value ELSE NULL END)AS sspc_ds_cir_fulfillment,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_ds_cir_current' THEN value ELSE NULL END )AS sspc_ds_cir_current,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_ds_cir_fulfillment_ratio' THEN value ELSE NULL END)AS sspc_ds_cir_fulfillment_ratio,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_ds_cir_demand_bytes' THEN value ELSE NULL END )AS sspc_ds_cir_demand_bytes,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_us_cir_fulfillment_ratio' THEN value ELSE NULL END)AS sspc_us_cir_fulfillment_ratio,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_ds_cir_demand_kbps' THEN value ELSE NULL END )AS sspc_ds_cir_demand_kbps,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_us_cir_demand_kbps' THEN value ELSE NULL END)AS sspc_us_cir_demand_kbps,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_us_cir_fulfillment' THEN value ELSE NULL END )AS sspc_us_cir_fulfillment,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_us_cir_demand_bytes' THEN value ELSE NULL END )AS sspc_us_cir_demand_bytes,
>LATEST_BY_OFFSET(CASE WHEN metric ='sspc_us_cir_current' THEN value ELSE NULL END)AS sspc_us_cir_current,
>count(*) as ct
>from Sspc_Usage_Stats_Transposedv3
>WINDOW TUMBLING (SIZE 5 MINUTES , GRACE PERIOD 1 MINUTES ) where  sspc=3536660
>group by sspc emit final ;

谁能给个提示?

推荐答案

EMIT FINAL 是数据驱动的，即只有当stream-time"提前超过窗口关闭时间.流时间"取决于观察到的输入记录的时间戳，因此，如果您停止发送输入记录，stream-time"没有进一步发展.

EMIT FINAL is data driven, i.e., it emit results only if "stream-time" advanced beyond the window close time. "Stream-time" depends on the observed timestamps of your input record, and thus, if you stop sending input records, "stream-time" does not advance further.

因此，如果您停止发送数据，最后一个窗口可能永远不会关闭，因此您永远不会看到它的结果.

Thus, if you stop sending data, the last window might never be closed, and thus you never see a result for it.

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