Changes between Initial Version and Version 1 of Ticket #25517


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Timestamp:
Oct 6, 2015, 12:41:59 PM (9 years ago)
Author:
Warren Smith
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  • Ticket #25517 – Description

    initial v1  
    1 When running on sqlite, with a {{{Concat()}}} expression used in the query, the {{{ConcatPair.coalesce()}}} method is called every time the SQL is generated. This is normal, expected, and AFAIK, correct behavior.
     1When running on sqlite, with a `Concat()` expression used in the query, the `ConcatPair.coalesce()` method is called every time the SQL is generated. This is normal, expected, and AFAIK, correct behavior.
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    3 The problem is that {{{ConcatPair.coalesce()}}} is NOT idempotent. So, EVERY time the SQL is generated, each expression within the {{{ConcatPair}}} instance is wrapped with an additional `COALESCE()` SQL function. If generated enough times, the SQL can reach a point where it will crash the sqlite query parser.
     3The problem is that `ConcatPair.coalesce()` is not idempotent. So, **//every//** time the SQL is generated, each expression within the {{{ConcatPair}}} instance is wrapped with an additional `COALESCE()` SQL function. If generated enough times, the SQL can reach a point where it will crash the sqlite query parser.
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    55This problem may not manifest itself in a typical request/response context, as the SQL with the additional `COALESCE()` calls will work identically to the original and the SQL may not be re-generated a sufficient number of times to crash the parser.
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    7 However, in a long-running process (where this bug was found), it can be easily triggered. For example, say I have a "base" queryset with a {{{Concat()}}} within an {{{.annotate()}}}. I never actually evaluate this queryset, but I use it to construct other querysets which I do evaluate. Because all of these querysets share the same instance of Query._annotations, evaluating ANY of these querysets will add an additional level of COALESCE() to the SQL generated by the others.
     7However, in a long-running process (where this bug was found), it can be easily triggered. For example, say I have a "base" queryset with a `Concat()` within an `.annotate()`. I never actually evaluate this queryset, but I use it to construct other querysets which I do evaluate. Because all of these querysets share the same instance of Query._annotations, evaluating ANY of these querysets will add an additional level of `COALESCE()` to the SQL generated by the others.
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    99I have a fix coded. I will submit a PR shortly.
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