What causes "Error fetching " in prestodb/presto?

Look at the cause chain of this exception — the root cause message names the actual validation that failed.

prestodb/presto · error · PageTransportErrorException

Error fetching

Error message

Error fetching

What it means

This is a wrapper error: after any failure inside the pages-response parsing block (bad headers, null body, corrupt smile stream), the client re-throws it as PageTransportErrorException with message 'Error fetching <request url>' and the original error as the cause, so all page-download failures surface uniformly with the failing URL and remote host.

Source

Thrown at presto-spark-base/src/main/java/com/facebook/presto/spark/execution/http/PrestoSparkHttpTaskClient.java:791

                String taskInstanceId = getTaskInstanceId(request, response);
                long token = getToken(request, response);
                long nextToken = getNextToken(request, response);
                boolean complete = getComplete(request, response);

                ResponseBody responseBody = response.body();
                if (responseBody == null) {
                    throw new PageTransportErrorException(
                            HostAddress.fromUri(request.url().uri()),
                            "Response body is null");
                }

                SliceInput input = new InputStreamSliceInput(responseBody.byteStream());
                List<SerializedPage> pages = ImmutableList.copyOf(readSerializedPages(input));
                PagesResponse pagesResponse = createPagesResponse(taskInstanceId, token, nextToken, pages, complete);
                return new PagesBaseResponse(response.code(), convertHeaders(response), pagesResponse);
            }
            catch (PageTransportErrorException e) {
                throw new PageTransportErrorException(
                        e.getRemoteHost(),
                        "Error fetching " + request.url(),
                        e);
            }
        }

        private static ListMultimap<OkHttpHeaderName, String> convertHeaders(Response response)
        {
            ImmutableListMultimap.Builder<OkHttpHeaderName, String> builder = ImmutableListMultimap.builder();
            for (String name : response.headers().names()) {
                for (String value : response.headers().values(name)) {
                    builder.put(OkHttpHeaderName.of(name), value);
                }
            }
            return builder.build();
        }

        private static String getTaskInstanceId(Request request, Response response)

View on GitHub (pinned to 55bb57d202)

Solutions

Look at the cause chain of this exception — the root cause message names the actual validation that failed.
Re-run the query; page transport errors are often transient after worker restarts.
Check the remote host in the exception and inspect that worker's logs for serialization/streaming faults.
Verify client/server Presto versions use the same serialized-page format.
If persistent, restart or replace the implicated worker and retry the query.

Defensive patterns

Strategy: try-catch

Validate before calling

// probe the worker endpoint before heavy page fetches
HttpResponse resp = httpClient.head(workerUrl);
if (resp.code() != 200) throw new IOException("Worker unhealthy: " + workerUrl);

Try / catch

try {
    client.getPagesRequest(...);
} catch (PageTransportErrorException e) {
    Throwable root = e;
    while (root.getCause() != null) root = root.getCause();
    log.error("Page fetch failed for %s, root cause: %s", e.getRemoteHost(), root.getMessage());
    throw e; // or retry transient causes (IOException, timeouts)
}

Prevention

Always inspect the cause chain; the outer message only names the URL.
Match Presto versions across client and workers.
Set sane read timeouts so stuck streams surface as retryable errors.
Monitor worker memory/health — OOM workers send truncated pages.

When it happens

Trigger: Any exception raised while processing a successful-status pages response: PageTransportErrorException from header/content-type/body validation, or an IOException while decoding serialized pages from the response stream.

Common situations: Worker returned malformed pages data (version mismatch in serialization format); network interruption mid-stream; any of errors 3750–3756 being wrapped; OOM in the worker returning truncated data.

Related errors

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/b056e163e7436c73. Report an issue: GitHub.