The bucket index consists of the first i bits in the hash function value.

(You can use the last i bits instead of the first i bits
I follow the presentation of the text book)



Parameter: i Insert( x, recordPtr(x) ) { k = h(x); // Genenral Hash function value j = first i bits of k; // Extensible hash function value Read bucket[j] (1 block) into memory; if ( bucket[j] block has space for a search key ) { Insert (x, recordPtr(x) ) into the block; Write block back to disk; return; } else { /*  bucket[j] disk block is full  */ Let i' = integer label of bucket[j] block; /*  Split bucket j (that has overflowed !!) into 2 buckets: j0 and j1  */ Allocate 2 disk block: j0 and j1; for ( each search key x' ∈ bucket[j] block ) do { k' = h(x'); // Find hash function value j' = the first i'+1 bits of k'; // Use 1 more bit ! if ( the last bit in j' == 0 ) store (x', recordPtr(x')) in block j0; else store (x', recordPtr(x')) in block j1; } (Result: ) /*  Update the tag of the new blocks j0 and j1  */ Tag the blocks j0 and j1 with the value i'+1; /* ====================================================== Update pointers to the bucket j (it is now 2 buckets) ====================================================== */ if ( i' < i ) { /* =============================================== Note: i' < i indicates that bucket[j'] and its "copy" points to the SAME disk block =============================================== */ Situation: /*  We have a spare bucket pointer No need to allocate more pointers !  */ bucket[j'<<1 + 0] = block address j0; bucket[j'<<1 + 1] = block address j1; Result: } else { Situation: /* ============================================= We need more pointers.... ============================================= */ double the bucket array (and copy bucket ptrs) as follows: bucket[j<<1 + 0] = block address j0 bucket[j<<1 + 1] = block address j1 Result: set i = i + 1; // Use 1 more bit to hash } /* ======================================================= We handled the overflow by allocating an extra bucket Now we can insert the key (and its rec ptr) ======================================================= */ Insert (x, recordPtr(x)) using the new configuration; } } 


Note:






Better solution:
