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Commitdfd8e6c

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Fix an issue with index scan using pg_trgm due to char signedness on different architectures.
GIN and GiST indexes utilizing pg_trgm's opclasses store sortedtrigrams within index tuples. When comparing and sorting each trigram,pg_trgm treats each character as a 'char[3]' type in C. However, thechar type in C can be interpreted as either signed char or unsignedchar, depending on the platform, if the signedness is not explicitlyspecified. Consequently, during replication between different CPUarchitectures, there was an issue where index scans on standby serverscould not locate matching index tuples due to the differing treatmentof character signedness.This change introduces comparison functions for trgm that explicitlyhandle signed char and unsigned char. The appropriate comparisonfunction will be dynamically selected based on the charactersignedness stored in the control file. Therefore, upgraded clusterscan utilize the indexes without rebuilding, provided the clusterupgrade occurs on platforms with the same character signedness as theoriginal cluster initialization.The default char signedness information was introduced in44fe30f,so no backpatch.Reviewed-by: Noah Misch <noah@leadboat.com>Discussion:https://postgr.es/m/CB11ADBC-0C3F-4FE0-A678-666EE80CBB07%40amazon.com
1 parent1aab680 commitdfd8e6c

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2 files changed

+45
-4
lines changed

2 files changed

+45
-4
lines changed

‎contrib/pg_trgm/trgm.h

Lines changed: 1 addition & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -40,15 +40,12 @@
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4141
typedefchartrgm[3];
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43-
#defineCMPCHAR(a,b) ( ((a)==(b)) ? 0 : ( ((a)<(b)) ? -1 : 1 ) )
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#defineCMPPCHAR(a,b,i) CMPCHAR( *(((const char*)(a))+i), *(((const char*)(b))+i) )
45-
#defineCMPTRGM(a,b) ( CMPPCHAR(a,b,0) ? CMPPCHAR(a,b,0) : ( CMPPCHAR(a,b,1) ? CMPPCHAR(a,b,1) : CMPPCHAR(a,b,2) ) )
46-
4743
#defineCPTRGM(a,b) do {\
4844
*(((char*)(a))+0) = *(((char*)(b))+0);\
4945
*(((char*)(a))+1) = *(((char*)(b))+1);\
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*(((char*)(a))+2) = *(((char*)(b))+2);\
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} while(0)
48+
externint(*CMPTRGM) (constvoid*a,constvoid*b);
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5350
#defineISWORDCHR(c)(t_isalnum(c))
5451
#defineISPRINTABLECHAR(a)( isascii( *(unsigned char*)(a) ) && (isalnum( *(unsigned char*)(a) ) || *(unsigned char*)(a)==' ') )

‎contrib/pg_trgm/trgm_op.c

Lines changed: 44 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -42,6 +42,9 @@ PG_FUNCTION_INFO_V1(strict_word_similarity_commutator_op);
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PG_FUNCTION_INFO_V1(strict_word_similarity_dist_op);
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PG_FUNCTION_INFO_V1(strict_word_similarity_dist_commutator_op);
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45+
staticintCMPTRGM_CHOOSE(constvoid*a,constvoid*b);
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int(*CMPTRGM) (constvoid*a,constvoid*b)=CMPTRGM_CHOOSE;
47+
4548
/* Trigram with position */
4649
typedefstruct
4750
{
@@ -107,6 +110,47 @@ _PG_init(void)
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MarkGUCPrefixReserved("pg_trgm");
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}
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113+
#defineCMPCHAR(a,b) ( ((a)==(b)) ? 0 : ( ((a)<(b)) ? -1 : 1 ) )
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/*
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* Functions for comparing two trgms while treating each char as "signed char" or
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* "unsigned char".
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*/
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staticinlineint
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CMPTRGM_SIGNED(constvoid*a,constvoid*b)
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{
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#defineCMPPCHAR_S(a,b,i) CMPCHAR( *(((const signed char*)(a))+i), *(((const signed char*)(b))+i) )
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returnCMPPCHAR_S(a,b,0) ?CMPPCHAR_S(a,b,0)
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: (CMPPCHAR_S(a,b,1) ?CMPPCHAR_S(a,b,1)
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:CMPPCHAR_S(a,b,2));
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}
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staticinlineint
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CMPTRGM_UNSIGNED(constvoid*a,constvoid*b)
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{
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#defineCMPPCHAR_UNS(a,b,i) CMPCHAR( *(((const unsigned char*)(a))+i), *(((const unsigned char*)(b))+i) )
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returnCMPPCHAR_UNS(a,b,0) ?CMPPCHAR_UNS(a,b,0)
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: (CMPPCHAR_UNS(a,b,1) ?CMPPCHAR_UNS(a,b,1)
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:CMPPCHAR_UNS(a,b,2));
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}
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/*
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* This gets called on the first call. It replaces the function pointer so
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* that subsequent calls are routed directly to the chosen implementation.
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*/
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staticint
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CMPTRGM_CHOOSE(constvoid*a,constvoid*b)
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{
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if (GetDefaultCharSignedness())
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CMPTRGM=CMPTRGM_SIGNED;
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else
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CMPTRGM=CMPTRGM_UNSIGNED;
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returnCMPTRGM(a,b);
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}
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110154
/*
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* Deprecated function.
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* Use "pg_trgm.similarity_threshold" GUC variable instead of this function.

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