integer divide by zero when using live / websocket

[FlorianLudwig]

Describe the bug

To Reproduce
Following the getting started:

1. I installed grafana, loki and promtail using docker-compose
2. "To see the logs, click Explore on the sidebar, select the Loki
   datasource in the top-left dropdown, and then choose a log stream using the
   Log labels button."
3. Query: {filename="/var/log/dnf.log"} term
4. Clicked Live
5. Waited a bit
6. "Bad Gateway" error appeared / loki crashed

Or maybe I first clicked live and then changed the query. In any case I was not yet able to reproduce this

Expected behavior

• no crash

Environment:

• local installation using docker-compose

loki, version k13-f86785b (branch: k13, revision: f86785b6)
  build user:       root@4bceb5defc91
  build date:       2020-04-14T16:33:11Z
  go version:       go1.13.10

Screenshots, Promtail config, or terminal output

loki_1      | level=info ts=2020-04-15T11:52:22.80544217Z caller=metrics.go:83 org_id=fake trace_id=7f4375a1c0697eb6 latency=fast query="{filename=\"/var/log/boot.log\"}" query_type=limited range_type=range length=1h0m1s step=1s duration=26.818979ms status=200 throughput_mb=0.0604907 total_bytes_mb=0.0016223
loki_1      | level=error ts=2020-04-15T11:52:43.590420331Z caller=http.go:227 msg="Error from client" err="websocket: close 1005 (no status)"
loki_1      | panic: runtime error: integer divide by zero
loki_1      | 
loki_1      | goroutine 344 [running]:
loki_1      | github.com/cortexproject/cortex/pkg/chunk.v11Entries.GetLabelWriteEntries(0x7fce00000000, 0x287a9a40287a8a4, 0xc000040820, 0xa, 0xc000040880, 0xb, 0x5265c00, 0x1aa4844, 0x4, 0xc000175280, ...)
loki_1      | 	/src/loki/vendor/github.com/cortexproject/cortex/pkg/chunk/schema.go:933 +0xd0c
loki_1      | github.com/cortexproject/cortex/pkg/chunk.schema.GetCacheKeysAndLabelWriteEntries(0xc00041a270, 0x1e6b8c0, 0x2bc7d00, 0x1717daa4ca4, 0x1717daa4da4, 0x1aa46cc, 0x4, 0x1aa4844, 0x4, 0xc000175280, ...)
loki_1      | 	/src/loki/vendor/github.com/cortexproject/cortex/pkg/chunk/schema.go:142 +0x456
loki_1      | github.com/cortexproject/cortex/pkg/chunk.(*seriesStore).calculateIndexEntries(0xc00010bb80, 0x1e4cd60, 0xc0001d2960, 0x1717daa4ca4, 0x1717daa4da4, 0x4ba07f3bc457104c, 0x1aa46cc, 0x4, 0x1717daa4ca4, 0x1717daa4da4, ...)
loki_1      | 	/src/loki/vendor/github.com/cortexproject/cortex/pkg/chunk/series_store.go:501 +0x1a8
loki_1      | github.com/cortexproject/cortex/pkg/chunk.(*seriesStore).PutOne(0xc00010bb80, 0x1e4cd60, 0xc0001d2960, 0x1717daa4ca4, 0x1717daa4da4, 0x4ba07f3bc457104c, 0x1aa46cc, 0x4, 0x1717daa4ca4, 0x1717daa4da4, ...)
loki_1      | 	/src/loki/vendor/github.com/cortexproject/cortex/pkg/chunk/series_store.go:464 +0x225
loki_1      | github.com/cortexproject/cortex/pkg/chunk.compositeStore.Put.func1(0x1717daa4ca4, 0x1717daa4da4, 0x1e6b260, 0xc00010bb80, 0x7fce9c7574e8, 0x2)
loki_1      | 	/src/loki/vendor/github.com/cortexproject/cortex/pkg/chunk/composite_store.go:81 +0xd3
loki_1      | github.com/cortexproject/cortex/pkg/chunk.compositeStore.forStores(0xc000111f20, 0x1, 0x1, 0x1717daa4ca4, 0x1717daa4da4, 0xc000aff860, 0x1b224b8, 0xc000aff888)
loki_1      | 	/src/loki/vendor/github.com/cortexproject/cortex/pkg/chunk/composite_store.go:217 +0x1e0
loki_1      | github.com/cortexproject/cortex/pkg/chunk.compositeStore.Put(0xc000111f20, 0x1, 0x1, 0x1e4cd20, 0xc000167260, 0xc000175300, 0x1, 0x1, 0x4a8a70, 0xc000276c60)
loki_1      | 	/src/loki/vendor/github.com/cortexproject/cortex/pkg/chunk/composite_store.go:80 +0x14b
loki_1      | github.com/grafana/loki/pkg/ingester.(*Ingester).flushChunks(0xc000133180, 0x1e4cd20, 0xc000167260, 0x4ba07f3bc457104c, 0xc000762540, 0x2, 0x2, 0xc000118360, 0x1, 0x1, ...)
loki_1      | 	/src/loki/pkg/ingester/flush.go:330 +0x7ec
loki_1      | github.com/grafana/loki/pkg/ingester.(*Ingester).flushUserSeries(0xc000133180, 0x1aa46cc, 0x4, 0x4ba07f3bc457104c, 0x0, 0x0, 0x0)
loki_1      | 	/src/loki/pkg/ingester/flush.go:217 +0x274
loki_1      | github.com/grafana/loki/pkg/ingester.(*Ingester).flushLoop(0xc000133180, 0xc)
loki_1      | 	/src/loki/pkg/ingester/flush.go:189 +0x304
loki_1      | created by github.com/grafana/loki/pkg/ingester.New
loki_1      | 	/src/loki/pkg/ingester/ingester.go:144 +0x360

[cyriltovena]

This is a problem only on master, I think @owen-d is fixing it.

[owen-d]

Yes, we accidentally added a build that had this problem. Please use the grafana/loki:1.4.1 build and not k13-f86785b. The problem was caused because that docker compose file uses grafana/loki:latest by default, which briefly pointed to the problematic build.

[FlorianLudwig]

@owen-d i changed the image as you suggested in #1945