Details
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Bug
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Status: Resolved
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Major
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Resolution: Fixed
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3.0.0
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None
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None
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None
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1
Description
If you upsert a doc, and then remove it at some point later, you will get LCB_ERR_DOCUMENT_NOT_FOUND. But, if you see if it exists after that, the lcb_respexists_is_found actually still returns true. Looking at the exists.cc, things look reasonable. Perhaps a document that has been removed recently still exists (marked as deleted) and we end up with LCB_SUCCESS in the rc for those?
This is really on latest master (though I marked it as 3.0.0, it is later than that)
Attachments
| For Gerrit Dashboard: CCBC-1187 | ||||||
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| # | Subject | Branch | Project | Status | CR | V |
| 123321,3 | PYCBC-818 Exists always returns true | master | couchbase-python-client | Status: MERGED | +2 | +1 |
| 127443,2 | CCBC-1187: lcb_respexists_is_found returns true for deleted documents. | master | libcouchbase | Status: MERGED | +2 | +1 |
Activity
As a side note, we are seeing intermittent segfaults with exists as well. The problem appears to be in the tracing that happens at the end of the lcb_wait call. If I call exists in a loop I can reproduce easily. A typical stack trace:
* thread #2, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x1)
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frame #0: 0x000000010388eba7 libcouchbase.2.dylib`::lcbtrace_span_add_tag_uint64(lcbtrace_SPAN *, const char *, uint64_t) [inlined] sllist_append(list=0x0000000101c28988, item=0x0000000101c29270) at sllist-inl.h:148:26
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frame #1: 0x000000010388eb9e libcouchbase.2.dylib`::lcbtrace_span_add_tag_uint64(lcbtrace_SPAN *, const char *, uint64_t) [inlined] lcb::trace::Span::add_tag(this=0x0000000101c28940, name="couchbase.context_info", copy=1, value=4324494992) at span.cc:409
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* frame #2: 0x000000010388eb6e libcouchbase.2.dylib`::lcbtrace_span_add_tag_uint64(span=0x0000000101c28940, name="couchbase.context_info", value=4324494992) at span.cc:99
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frame #3: 0x0000000101f10da4 _libcouchbase.cpython-37m-darwin.so`pycbc_propagate_context_info(span=0x0000000101c001a0, dest=0x0000000101c28940) at ext.c:2581:5 [opt]
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frame #4: 0x0000000101f110e3 _libcouchbase.cpython-37m-darwin.so`pycbc_span_report(tracer=<unavailable>, span=0x0000000101c001a0) at ext.c:2761:5 [opt]
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frame #5: 0x000000010388e826 libcouchbase.2.dylib`::lcbtrace_span_finish(lcbtrace_SPAN *, uint64_t) [inlined] lcb::trace::Span::finish(this=0x0000000101c001a0, now=<unavailable>) at span.cc:366:9
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frame #6: 0x000000010388e801 libcouchbase.2.dylib`::lcbtrace_span_finish(span=0x0000000101c001a0, now=<unavailable>) at span.cc:71
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frame #7: 0x00000001038482be libcouchbase.2.dylib`::mcreq_dispatch_response(mc_PIPELINE *, mc_PACKET *, lcb::MemcachedResponse *, lcb_STATUS) at handler.cc:481:5
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frame #8: 0x0000000103848118 libcouchbase.2.dylib`::mcreq_dispatch_response(pipeline=0x0000000101e24490, req=<unavailable>, res=0x00007ffeefbfe120, immerr=LCB_SUCCESS) at handler.cc:1201
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frame #9: 0x000000010387faf9 libcouchbase.2.dylib`lcb::Server::try_read(this=0x0000000101e24490, ctx=<unavailable>, ior=0x0000000101e25be8) at mcserver.cc:0
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frame #10: 0x00000001038812ae libcouchbase.2.dylib`on_read(ctx=0x0000000101e25ba0, (null)=<unavailable>) at mcserver.cc:579:26
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frame #11: 0x0000000103819d09 libcouchbase.2.dylib`E_handler [inlined] invoke_read_cb(ctx=<unavailable>, nb=47) at ctx.c:255:5
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frame #12: 0x0000000103819cee libcouchbase.2.dylib`E_handler(sock=<unavailable>, which=2, arg=0x0000000101e25ba0) at ctx.c:282
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frame #13: 0x0000000103803132 libcouchbase.2.dylib`run_loop(io=0x0000000101c1ce00, is_tick=0) at plugin-select.c:309:17
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frame #14: 0x000000010388e6dd libcouchbase.2.dylib`::lcb_wait(instance=0x0000000101c27840, flags=<unavailable>) at wait.cc:109:5
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frame #15: 0x0000000101f1b172 _libcouchbase.cpython-37m-darwin.so`pycbc_common_vars_wait [inlined] pycbc_oputil_wait_common(self=<unavailable>, context=<unavailable>) at oputil.c:702:5 [opt]
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frame #16: 0x0000000101f1b132 _libcouchbase.cpython-37m-darwin.so`pycbc_common_vars_wait(cv=0x00007ffeefbfe6b0, self=0x000000010545ed70, context=<unavailable>) at oputil.c:205 [opt]
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frame #17: 0x0000000101f145cb _libcouchbase.cpython-37m-darwin.so`get_common(self=0x000000010545ed70, args=<unavailable>, kwargs=0x00000001054
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It appears that the list somehow has gotten corrupted. Not sure how/why.
However this isn't the real topic of this bug report – it is the fact that the lcb_respexists_is_found returns true when the document has been recently deleted. This happens hitting 5.5.6 and 6.5 (didn't try others). I doubt it it related to the segfault above, so maybe worth a second bug report just for it.
The segfault mentioned above is CCBC-1215 - and there is a changelist for it. This ticket is just for is_found returning true for deleted docs.
Since we know whether or not the document has been deleted, we can either let is_found continue to return true for this case and add a new api for is_deleted, or just change the logic to return false if the doc has been deleted.
To me, the latter is more logical, so I'll do that, and we can discuss...
Build couchbase-server-7.0.0-3115 contains libcouchbase commit 207d15d with commit message:
CCBC-1187: lcb_respexists_is_found returns true for deleted documents.
This does happen on 6.5 and earlier (5.5.6 for instance). If the key was never in the server, things are correct. But if it was we fail. My test upserts, makes sure it is there with a get, then removes and makes sure a get returns a LCB_ERR_DOCUMENT_NOT_FOUND, then tries exists and it gets true from lcb_respexists_is_found.